T. Abe and R. Seki
Various quantities of an attractively interacting fermion system at the unitary limit are determined by extrapolating Monte Carlo results of low-density neutron matter. Smooth extrapolation in terms of $1/(k_F a_0)$ ($k_F$ is the Fermi momentum, and $a_0$ S-wave scattering length) is found with the quantities examined: the ground-state energy, the pairing energy gap, and the critical temperature of the normal-to-superfluid phase transition. We emphasize proximity of the physics of low-density neutron matter to that at the unitary limit. The extrapolated quantities are in a reasonable agreement with those in the literature.
T. Abe and R. Seki
To be added.
S. Profumo, M.J. Ramsey-Musolf, and G. Shaughnessy
To be added.
J. Kile and M. Ramsey-Musolf
To be added.
S. Tulin, M.J. Ramsey-Musolf and S. Su
To be added.
K.S.M. Lee, Z. Ligeti, I.W. Stewart, and F.J. Tackmann
To be added.
P. Vogel
The status of the search for neutrinoless double beta decay is reviewed. The effort to reach the sensitivity needed to cover the effective Majorana neutrino mass corresponding to the degenerate and inverted mass hierarchy is described. Various issues concerning the theory (and phenomenology) of the relation between the 0\nu\beta\beta decay rate and the absolute neutrino mass scale are discussed, in particular the issue of mechanism of the 0\nu\beta\beta decay. Finally, the relation between the neutrino magnetic moments and the charge conjugation property (Dirac vs. Majorana) is described.
D. O'Connell, M.J. Ramsey-Musolf, and M.B. Wise
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M. Gorchtein, N.F. Bell, M.J. Ramsey-Musolf, P. Vogel and P. Wang
To be added.
M. Gorchtein
To be added.
R.J. Erwin, J. Kile, M.J. Ramsey-Musolf, P. Wang
To be added.
M.J. Ramsey-Musolf
To be added.
S. Profumo, M.J. Ramsey-Musolf, and S. Tulin
To be added.
J.F. Beacom, N.F. Bell, and G.D. Mack
To be added.
N.F. Bell, M. Gorshteyn, M.J. Ramsey-Musolf, P. Vogel and P. Wang
To be added.
Not used.
V. Cirigliano, G. Ecker, M. Eidenmuller, R. Kaiser, A. Pich, and J. Portoles
To be added.
M.J. Ramsey-Musolf
To be added.
R.J. Erwin
To be added.
V. Cirigliano and B. Grinstein
To be added.
B. Bistrovic, R.J. Erwin, J.W. Negele, and M.J. Ramsey-Musolf
To be added.
M.J. Ramsey-Musolf and S.A. Page
Studies of the strangeness changing hadronic weak interaction have produced a number of puzzles that have so far evaded a complete explanation within the Standard Model. Their origin may lie either in dynamics peculiar to weak interactions involving strange quarks or in more general aspects of the interplay between strong and weak interactions. In principle, studies of the strangeness conserving hadronic weak interaction using parity violating hadronic and nuclear observables provide a complementary window on this question. However, progress in this direction has been hampered by the lack of a suitable theoretical framework for interpreting hadronic parity violation measurements in a model-independent way. Recent work involving effective field theory ideas has led to the formulation of such a framework while motivatin ghte development of a number of new hadronic parity violation experiments in few-body systems. In this article, we review these recent developments and discuss the prospects and opportunities for further experimental and theoretical progress.
M.J. Ramsey-Musolf and S. Su
To be added.
V. Cirigliano, C. Lee, M.J. Ramsey-Musolf and S. Tulin
To be added.
C.-P. Liu, W.C. Haxton, M.J. Ramsey-Musolf, R.G.E. Timmermans, and A.E.L. Dieperink
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R.J. Erwin, J. Kile, M.J. Ramsey-Musolf and P. Wang
We use the scale of of neutrino mass to derive model-independent naturalness constraints on possible contributions to muon decay Michel parameters from new physics above the electroweak symmetry-breaking scale. Focusing on Dirac neutrinos, we obtain a complete basis of effective dimension four and dimension six operators that are invariant under the gauge symmetry of the Standard Model and that contribute to both muon decay and neutrino mass. We show that -- in the absence of fine tuning -- the most stringent bounds on chirality-changing operators relevant to muon decay arise from one-loop contributions to neutrino mass. The bounds we obtain on their contributions to the Michel parameters are four or more orders of magnitude stronger than bounds previously obtained in the literature. We also show that there eixst chirality-changing operators that contribute to muon decay but whose flavor structure allows them to evade neutrino mass naturalness bounds. We discuss the implications of our analysis for the interpretation of muon decay experiments.
N.F. Bell, E. Pierpaoli, and K. Sigrdson
We investigate signatures of neutrino scattering in the Cosmic Microwave Background (CMB) and matter power spectra, and the extent to which present cosmological data can distinguish between a free streaming or tightly coupled fluid of neutrinos. If neutrinos have strong non-standard interactions, for example, through the coupling of neutrinos to a light boson, they may be kept in equilibrium until late times. We show how the power spectra for these models differ from more conventional neutrino scenarios, and use CMB and large scale structure data to constrain these models. The present data can accommodate a number of tightly-coupled relativistic degrees of freedom, and none of the interacting-neutrino scenarios considered is ruled out by current data, contrary to the claim in [1]. Neutrino mass limits are quite different, depending on how many neutrino species interact. We show that CMB polarization data improves the constraints on the number of massless neutrinos, while the Lyman-$\alpha$ power spectrum improves the limits on the neutrino mass
V. Cirigliano and D. Pirjol
To be added.
N.F. Bell, V. Cirigliano, M.J. Ramsey-Musolf, P. Vogel, and M.B. Wise
We derive model-independent, "naturalness" upper bounds on the magnetic moments $\mu_\nu$, of Dirac neutrinos generated by physics above the scale of electroweak symmetry breaking. In the absence of fine-tuning of effective operator coefficients, we find that current information on neutrino mass implies that $|\mu_\nu|\lesssim 10^{-15} Bohr magnetons. This bound is several orders of magnitude stronger than those obtained from analysis of solar and reactor neutrino data and astrophysical observations.
V. Cirigliano, G. Ecker, M. Eidenmuller, R. Kaiser, A. Pich, and J. Portoles
To be added.
B. Bistrovic, R. Erwin, J. Negele, and M.J. Ramsey-Musolf
To be added
C. Lee, V. Cirigliano, and M.J. Ramsey-Musolf
To be added
K. Abazajian, N.E. Bell, G.M. Fuller and Y.Y.Y. Wong
To be added
G. Prezeau, A. Kurylov, and M.J. Ramsey-Musolf
To be added
J. Beacom, N. Bell, and G. Bertone
To be added
J. Erler and M.J. Ramsey-Musolf
To be added
Z. Shu, C.M. Maekawa, B.R. Holstein, M.J. Ramsey-Musolf and U. van Kolck
To be added
L. Diaconescu and M.J. Ramsey-Musolf
To be added
J. Erler and M.J. Ramsey-Musolf
To be added
V. Cirigliano, A. Kurylov, M.J. Ramsey-Musolf and P. Vogel
To be added
V. Cirigliano, G. Ecker, M. Eidemuller, A. Pich and J. Portoles
To be added
T. Abe, R. Seki, and A.N. Kocharian
Thermal properties of single species nucleon matter are investigated assuming a simple form of the nucleon-nucleon interaction. The nucleons are placed on a cubic lattice, hopping from site to site and interacting through a spin-dependent force, as in the extended, attractive Hubbard model. A mean field calculation in the Hartree-Fock Bogoliubov approximation suggests that the superfluid ground state generated by strong nucleon pairing undergoes a second-order phase transition to a normal state as the temperature increases. The calculation is shown to lead to a promising description of the thermal properties of low-density neutron matter. A possibility of a density wave phase is also examined.
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V. Cirigliano, H. Neufeld, and H. Pichl
To be added
V. Cirigliano, G. Ecker, H. Neufeld, and A. Pich
We perform a complete analysis of isospin breaking in $K\rightarrow 2\pi$ amplitudes in chiral perturbation theory, including both strong isospin violation $(m_u\neq m_d)$ and electromagnetic corrections to next-to-leading order in the low-energy expansion. The unknown chiral couplings are estimated at leading order in the $1/N_c$ expansion. We study the impact of isospin breaking on CP conserving amplitudes and rescattering phases. In particular, we extract the effective couplins $g_i$ and $g_{27}$ from a fit to $K\rightarrow \pi\pi$ branching ratios, finding small deviations from the isospin-limit case. The ratio Re$A_0$/Re$A_2$ measuring the $\Delta I=1/2$ enhancement is found to decrease from 22.2$\pm$0.1 in the isospin limit to 20.3$\pm$0.5 in the presence of isospin breaking. We also analyse the effect of isospin violation on the CP violation parameter $\epsilon'$, finding a destructive interference between three different sources of isospin violation. Within the uncertainties of large-$N_c$ estimates for the low-energy constants, the isospin violating correction for $\epsilon'$ is below 15\%
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A. Kurylov, M.J. Ramsey-Musolf, and S. Su
To be added
M.J. Ramsey-Musolf
I discuss several physics issues that can be addressed through the present and future program of parity-violating electron scattering measurements. In particular, I focus on strange quark form factors, hadronic effects in electroweak radiative corrections, and physics beyond the Standard Model
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A. Kurylov, M.J. Ramsey-Musolf, and S. Su.
We compute the one-loop supersymmetric (SUSY) contributions to the weak charges of the electron ($Q_W^e$), proton ($Q_W^p$), and cesium nucleus ($Q_W^{\rm Cs}$) in the Minimal Supersymmetric Standard Model (MSSM). Such contributions can generate several percent corrections to the corresponding Standard Model values. The magnitudes of the SUSY loop corrections to $Q_W^e$ and $Q_W^p$ are correlated over nearly all of the MSSM parameter space and result in an increase in the magnitudes of these weak charges. In contrast, the effects on $Q_W^{\rm Cs}$ are considerably smaller and are equally likely to increase or decrease its magnitude. Allowing for R-parity violation can lead to opposite sign relative shifts in $Q_W^e$ and $Q_W^p$, normalized to the corresponding Standard Model values. A comparison of $Q_W^p$ and $Q_W^e$ measurements could help distinguish between different SUSY scenarios.
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G. Prezeau, M.J. Ramsey-Musolf, and P. Vogel.
We analyze neutrinoless double $\beta$-decay ($\nbb$-decay) mediated by heavy particles from the standpoint of effective field theory. We show how symmetries of the $\nbb$-decay quark operators arising in a given particle physics model determine the form of the corresponding effective, hadronic operators. We classify the latter according to their symmetry transformation properties as well as the order at which they appear in a derivative expansion. We apply this framework to several particle physics models, including R-parity violating supersymmetry (RPV SUSY) and the left-right symmetric model (LRSM) with mixing and a right-handed Majorana neutrino. We show that, in general, the pion exchange contributions to $\nbb$-decay dominate over the short-range four-nucleon operators. This confirms previously published RPV SUSY results and allows us to derive new constraints on the masses in the LRSM. In particular, we show how a non-zero mixing angle $\zeta$ in the left-right symmetry model produces a new potentially dominant contribution to $\nbb$-decay that substantially modifies previous limits on the masses of the right-handed neutrino and boson stemming from constraints from $\nbb$-decay and vacuum stability requirements.
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J. Erler, A. Kurylov, and M.J. Ramsey-Musolf
We address the physics implications of a precision determination of the weak charge of the proton, $\qwp$, from a parity violating elastic electron proton scattering experiment to be performed at the Jefferson Laboratory. We present the Standard Model (SM) expression for $\qwp$ including one-loop radiative corrections, and discuss in detail the theoretical uncertainties and missing higher order QCD corrections. Owing to a fortuitous cancellation, the value of $\qwp$ is suppressed in the SM, making it a unique place to look for physics beyond the SM. Examples include extra neutral gauge bosons, supersymmetry, and leptoquarks. We argue that a $\qwp$ measurement will provide an important complement to both high energy collider experiments and other low energy electroweak measurements. The anticipated experimental precision requires the knowledge of the ${\cal O}(\alpha_s)$ corrections to the pure electroweak box contributions. We compute these contributions for $\qwp$, as well as for the weak charges of heavy elements as determined from atomic parity violation.
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A. Kurylov, M.J. Ramsey-Musolf, and S. Su.
We compute the supersymmetric (SUSY) contributions to $\nu$ (${\bar\nu}$)-nucleus deep inelastic scattering in the Minimal Supersymmetric Standard Model (MSSM). We consider the ratio of neutral current to charged current cross sections, $\rnu$ and $\rnubar$, and compare with the deviations of these quantities from the Standard Model predictions implied by the recent NuTeV measurement. After performing a model-independent analysis, we find that SUSY loop corrections generally have the opposite sign from the NuTeV anomaly. We discuss one scenario in which a right-sign effect arises, and show that it is ruled out by other precision data. We also study for R parity-violating (RPV) contributions. Although RPV effects could, in principle, reproduce the NuTeV anomaly, such a possibility is also ruled out by other precision electroweak measurements.
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C.-P. Liu, G. Prezeau, and M.J. Ramsey-Musolf
We compute contributions to the parity-violating (PV) inelastic electron-deuteron scattering asymmetry arising from hadronic PV. While hadronic PV effects can be relatively important in PV threshold electro- disintegration, we find that they are highly suppressed at quasielastic kinematics. The interpretation of the PV quasielastic asymmetry is, thus, largely unaffected by hadronic PV
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S.-L. Zhu and M.J. Ramsey-Musolf
We study the off-diagonal Goldberger-Treiman relation (ODGTR) and its discrepancy (ODGTD) in the $N$, $\Delta$, $\pi$ sector through ${\cal O}(p^2)$ using heavy baryon chiral perturbation theory. To this order, the ODGTD and axial vector $N$ to $\Delta$ transition radius are determined solely by low energy constants. Loop corrections appear at ${\cal O}(p^4)$. For low-energy constants of natural size, the ODGTD would represent a $\sim 2\%$ correction to the ODGTR. We discuss the implications of the ODGTR and ODGTD for lattice and quark model calculations of the transition form factors and for parity-violating electroexcitation of the $\Delta$.
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H.-W. Hammer, S.J. Puglia, M.J. Ramsey-Musolf, and S.-L. Zhu
We analyze the $q^2$-dependence of the strange magnetic form factor, $\GMS(q^2)$, using heavy baryon chiral perturbation theory (HB$\chi$PT) and dispersion relations. We find that in HB$\chi$PT a significant cancellation occurs between the ${\cal O}(p^2)$ and ${\cal O}(p^3)$ loop contributions. Consequently, the slope of $\GMS$ at the origin displays an enhanced sensitivity to an unknown ${\cal O}(p^3)$ low-energy constant. Using dispersion theory, we estimate the magnitude of this constant, show that it may have a natural size, and conclude that the low-$q^2$ behavior of $\GMS$ could be dominated by nonperturbative physics. We also discuss the implications for the interpretation of parity-violating electron scattering measurements used to measure $\GMS(q^2)$.
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M.J. Ramsey-Musolf and Mark B. Wise
We compute the hadronic light-by-light scattering contributions to the muon anomalous magnetic moment, $\amulbl$, in chiral perturbation theory. We obtain the model-independent, leading and subleading logarithmic contributions to this quantity, whose sum depends on a low-energy constant entering pseudoscalar meson decay into a charged lepton pair. The uncertainty introduced by this constant is comparable in magnitude to the uncertainty entering the leading-order vacuum polarization contributions to the anomalous moment. It may be reduced to some extent through an improved measurement of the $\pi^0\to e^+ e^-$ branching ratio. However, the dependence of $\amulbl$ on non-logarithmically enhanced effects cannot be constrained except through the measurement of the anomalous moment itself. The extraction of information on new physics would require a future experimental value for the anomalous moment differing significantly from the result originally reported by the E821 collaboration.
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S.-L. Zhu, G. Sacco, and M.J. Ramsey-Musolf
We compute the chiral corrections to octet baryon axial currents through ${\cal O} (p^3)$, including both octet and decuplet baryon intermediate states. We find that, in contrast to the situation at ${\cal O} (p^2)$, there exist no cancellations between ocetet and decuplet contributions at ${\cal O} (p^3)$. Consequently, the ${\cal O} (p^3)$ corrections spoil the expected scaling behavior of the chiral expression. We discuss this result in terms of the $1/N_c$ expansion. We also consider the implications for determination of the strange quark contribution to the nucleon spin from polarized deep inelastic scattering data
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C-S Huang, C. Liu, and S-L Zhu
The HQET sum rule analysis for the $\Lambda_b$ matrix element of the four-quark operator relevant to its lifetime is reported. Our main conclusion is that the lifetime ratio $\tau(\Lambda_b)/\tau(B^0)$ can be as low as $0.91$
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A. Kurylov and M.J. Ramsey-Musolf
We compute the complete one-loop contributions to low-energy charged current weak interaction observables in the Minimal Supersymmetric Standard Model (MSSM). We obtain the constraints on the MSSM parameter space which arise when precision low-energy charged current data are analyzed in tandem with measurements of the muon anomaly. While the data allow the presence of at least one light neutralino, they also imply a pattern of mass splittings among first and second generation sleptons and squarks which contradict predictions of widely used models for supersymmetry breaking mediation.
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S.-L. Zhu, C.M. Maekawa, G. Sacco, B.R. Holstein, and M.J. Ramsey-Musolf
We analyze the degree to which parity-violating (PV) electroexcitation of the $\Delta(1232)$ resonance may be used to extract the weak neutral axial vector transition form factors. We find that the axial vector electroweak radiative corrections are large and theoretically uncertain, thereby modifying the nominal interpretation of the PV asymmetry in terms of the weak neutral form factors. We also show that, in contrast to the situation for elastic electron scattering, the axial $N\to\Delta$ PV asymmetry does not vanish at the photon point as a consequence of a new term entering the radiative corrections. We argue that an experimental determination of these radiative corrections would be of interest for hadron structure theory, possibly shedding light on the violation of Hara's theorem in weak, radiative hyperon decays.
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S.-L. Zhu, C.M. Maekawa, B.R. Holstein, and M.J. Ramsey-Musolf
We analyze the real photon asymmetry $A^\pm_\gamma$ for the parity violating (PV) $\pi^\pm$ production on the $\Delta$ resonance via the reactions ${\vec \gamma} + p \to \Delta^+ \to \pi^+ + n$ and ${\vec \gamma} + d \to \Delta^0 + p \to \pi^- + p + p$. This asymmetry is nonvanishing due to a new PV $\gamma N \Delta$ coupling constant, $d^\pm_\Delta$. We argue that an experimental determination of this coupling would be of interest for hadron dynamics, possibly shedding light on the S-wave/P-wave puzzle in the hyperon nonleptonic decays and the violation of Hara's theorem in weak radiative hyperon decays. A measurement of $\alrd^\pm$ would also help clarify the interpretation of a planned measurement of the PV $\pi$ electroproduction asymmetry on the $\Delta^+$ resonance, where $d_\Delta^+$ introduces the dominant theoretical uncertainty.
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Shi-Lin Zhu, S. Puglia$, B.R. Holstein, and M. J. Ramsey-Musolf
We compute the photon asymmetry $B_\gamma$ for near threshold parity violating (PV) pion photoproduction through sub-leading order. We show that sub-leading contributions involve a new combination of PV couplings not included in previous analyses of hadronic PV. We argue that existing constraints on the leading order contribution to $B_\gamma$ -- obtained from the PV $\gamma$-decay of $^{18}$F -- suggest that the impact of the subleading contributions may be more significant than expected from naturalness arguments.
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W.C. Haxton, C.-P. Liu, and M.J. Ramsey-Musolf
Standard analyses of low-energy NN and nuclear parity-violating observables have been based on a $\pi-$, $\rho-$, and $\omega-$exchange model capable of describing all five independent $s-p$ partial waves. Here a parallel analysis is performed for the one-body, exchange-current, and nuclear polarization contributions to the anapole moments of $^{133}$Cs and $^{205}$Tl. The resulting constraints are not consistent, though there remains some degree of uncertainty in the nuclear structure analysis of the atomic moments
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B.W. Filippone and X. Ji
We present an overview of recent experimental and theoretical advances in our understanding of the spin structure of protons and neutrons
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U. van Kolck et al,
To be added
L. Diaconescu, R. Schiavilla, U. van Kolck
To be added
S.R. Beane, P.F. Bedaque, L. Childress, A. Kryjevski, J. McGuire, and U. van Kolck
To be added
M. Malheiro, S.R. Beane, D.R. Phillips, and U. van Kolck
Compton scattering on the deuteron is studied in the framework of baryon chiral perturbation theory to third order in small momenta, for photon energies of order the pion mass. The scattering amplitude is a sum of one- and two-nucleon mechanisms with no undetermined parameters. Our results are in good agreement with the intermediate energy experimental data, and a comparison is made with the recent higher-energy data obtained at SAL.
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C.M. Maekawa, J.S. Veiga, and U. van Kolck
The anapole form factor of the nucleon is calculated in chiral perturbation theory to sub-leading order. This is the lowest order in which the isovector anapole form factor does not vanish. The anapole moment depends on counterterms that reflect short-range dynamics, but the momentum dependence of the form factor is determined by pion loops in terms of parameters that could in principle be fixed from other processes. If these parameters are assumed to have natural size, the sub-leading corrections do not exceed $\sim$ 30\% at momentum $Q\sim 300$ MeV.
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U. van Kolck
Basic ideas underlying the application of effective field theories to strong interactions are discussed, and some of their consequences to few-nucleon systems are sketched.
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U. van Kolckm J.A. Niskanen, and G.A. Miller
Chiral effective field theory predicts a specific charge symmetry violating amplitude for pion production. This term is shown to provide a potentially large contribution to the forward-backward asymmetry in the angular distribution for the reaction $pn\to d\pi^0$.
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C. Hanhart, U. van Kolck, and G.A. Miller
Production of $p$-wave pions in nucleon-nucleon collisions is studied according to an improved power counting that embodies the constraints of chiral symmetry. Contributions from the first two non-vanishing orders are calculated. We find reasonable convergence and agreement with data for a spin-triplet cross section in $pp\rightarrow pp\pi^0$, with no free parameters. Agreement with existing data for a spin-singlet cross section in $pp\rightarrow pn\pi^+$ constrains a short-range operator shown recently to contribute significantly to the three-nucleon potential.
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C.M. Maekawa and U. Van Kolck
The anapole form factor of the nucleon is calculated in chiral perturbation theory in leading order. To this order, the form factor originates from the pion cloud, and is proportional to the non-derivative parity-violating pion-nucleon coupling. The momentum dependence of the form factor ---and in particular, its radius--- is completely determined by the pion mass.
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C.M. Maekawa, J.C. Pupin, and M.R. Robilotta
We show that the tail of the chiral two-pion exchange nucleon-nucleon potential is proportional to the $\pi N$ scalar form factor and discuss how it can be translated into effective scalar meson interactions. We then construct a kernel for the process $NN\rightarrow\pi NN$, due to the exchange of two pions, which may be used in either three body forces or pion production in $NN$ scattering. Our final expression involves a partial cancellation among three terms, due to chiral symmetry, but the net result is still important. We also find that, at large internucleon distances, the kernel has the same spatial dependence as the central $NN$ potential and we produce expressions relating these processes directly
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H.-M. Mueller, S.E. Koonin, R. Seki, and U. van Kolck
We investigate nuclear matter on a cubic lattice. An exact thermal formalism is applied to nucleons with a Hamiltonian that accommodates on-site and next-neighbor parts of the central, spin- and isospin-exchange interactions. We describe the nuclear matter Monte Carlo methods which contain elements from shell model Monte Carlo methods and from numerical simulations of the Hubbard model. We show that energy and basic saturation properties of nuclear matter can be reproduced. Evidence of a first-order phase transition from an uncorrelated Fermi gas to a clustered system is observed by computing mechanical and thermodynamical quantities such as compressibility, heat capacity, entropy and grand potential. We compare symmetry energy and first sound velocities with literature and find reasonable agreement.
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D. Huber, J.L. Friar, A. Nogga, H. Witala, and U. van Kolck
We include two new three-nucleon-force terms of pion-range -- short-range form in our momentum-space calculations for the three-nucleon continuum. These two terms are expected by chiral perturbation theory to be non-negligible. We study the effects of these terms in elastic neutron-deuteron scattering and pay special attention to the neutron vector analyzing power $A_y$.
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H. Nakamura and R. Seki
We investigate a domain-structured source in the pion interferometry of relativistic nuclear collisions. The source emits coherent pions intermittently with the background of chaotic pions. The coherent pions examined are either of a general nature or of disoriented chiral condensate. Two- and three-pion correlations for the source are shown to agree well with the recent NA44 experimental data
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H. Nakamura and R. Seki
Two- and three-pion correlations are investigated in cases when disoriented chiral condensate (DCC) occurs. A chaoticity and weight factor are used as measures of two- and three-pion correlations, and the various models for DCC are investigated. Some models are found to yield the chaoticity and weight factor in a reasonable agreement with recent experimental data
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H. Nakamura and R. Seki
Two- and three-pion correlation functions are investigated for a source that is not fully chaotic. Various models are examined to describe the source. The chaoticity and weight factor are evaluated in each model as measures of the strength of correlations and compared to experimental results. A new measure of three-pion correlation is also suggested
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J.~F. Beacom and P. Vogel
We find that magnetic neutrino-electron scattering is unaffected by oscillations for vacuum mixing of Dirac neutrinos with only diagonal moments and for Majorana neutrinos with two flavors. For MSW mixing, these cases again obtain, though the effective moments can depend on the neutrino energy. Thus, e.g., the magnetic moments measured with $\bar{\nu}_e$ from a reactor and $\nu_e$ from the Sun could be different. With minimal assumptions, we find a new limit on $\mu_{\nu}$ using the SuperKamiokande solar neutrino data: $\mu_{\nu} \le 2.0\times 10^{-10} \mu_B$ with the published 504-days data, and $\mu_{\nu} \le 1.6 \times 10^{-10} \mu_B$ with the preliminary 708-days data (with two new low-energy bins), both at 90\% CL
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T.D. Shoppa, S.E. Koonin, and R. Seki
We investigate quantal perturbations of the interferometric correlations of charged bosons by the Coulomb field of an instantaneous, charged source. The source charge increases the apparent source size by weakening the correlation at non-zero relative momenta. The effect is strongest for pairs with a small total momentum and is stronger for kaons than for pions of the same momenta. The low-energy data currently available are well described by this effect. A simple expression is proposed to account for the effect
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H. Nakamura and R. Seki
Three-pion interferometry is investigated for new information on the space-time structure of the pion source created in ultra-relativistic heavy-ion collisions. The two- and three-pion correlations are numerically computed for incoherent source functions based on the Bjorken hydrodynamical model, over a wide range of the kinematic variables. New information provided by three-pion interferometry, different from that provided by two-pion interferometry, should appear in the phases of the Fourier transform of the source function. Variables are identified that would be sensitive to the phases and suitable for observation. For a positive, chaotic source function, however, a variation of the three-pion phase is found to be difficult to extract from experiments. Effects of asymmetry of the source function are also examined
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R. Seki and I. Tanihata
A model-independent analysis is applied to the determination of the nuclear density distributions of neutron-rich nuclei from proton scattering data. Recent GSI ${}^6$He data are used to demonstrate the feasibility and usefulness of such an analysis for a direct determination of the distributions. We examine how the determination can be improved by combining the data with other information such as the charge distribution of the nucleus and the density distribution of its neighboring closed-shell nucleus.
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U. van Kolck
I discuss neutral pion photoproduction on the deuteron and pion production in nucleon-nucleon collisions. The first reaction is {\it predicted} at threshold in the effective field theory (EFT) approach with {\it non-}perturbative pions. This is the first nuclear EFT prediction that differs significantly from conventional model predictions, and recent SAL data clearly favors the EFT result. The second reaction is currently not understood near threshold, and thus offers another opportunity to contrast EFT and {\it ad hoc} model approaches
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U. van Kolck
I briefly review the main developments since the first workshop on the nuclear applications of Effective Field Theories, held in 1998. A summary of some of the goals P. Bedaque, M. Savage, R. Seki and I had in mind for this second workshop is also presented.
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P. Vogel and J.F. Beacom
The reaction $\bar{\nu}_e + p \rightarrow e^+ + n$ is very important for low-energy ($E_\nu \lesssim 60$ MeV) antineutrino experiments. In this paper we calculate the positron angular distribution, which at low energies is slightly backward. We show that weak magnetism and recoil corrections have a large effect on the angular distribution, making it isotropic at about 15 MeV and slightly forward at higher energies. We also show that the behavior of the cross section and the angular distribution can be well-understood analytically for $E_\nu \lesssim 60$ MeV by calculating to ${\cal O}(1/M)$, where $M$ is the nucleon mass. The correct angular distribution is useful for separating $\bar{\nu}_e + p \rightarrow e^+ + n$ events from other reactions and detector backgrounds, as well as for possible localization of the source (e.g., a supernova) direction. We comment on how similar corrections appear for the lepton angular distributions in the deuteron breakup reactions $\bar{\nu}_e + d \rightarrow e^+ + n + n$ and $\nu_e + d \rightarrow e^- + p + p$. Finally, in the reaction $\bar{\nu}_e + p \rightarrow e^+ + n$, the angular distribution of the outgoing neutrons is strongly forward-peaked, leading to a measurable separation in positron and neutron detection points, also potentially useful for rejecting backgrounds or locating the source direction.
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J.L. Friar and U. van Kolck
Charge-independence breaking due to the pion-mass difference in the (chiral) two-pion-exchange nucleon-nucleon force is investigated. A general argument based on symmetries is presented that relates the charge-symmetric part of that force to the proton-proton case. The static potential linear in that mass difference is worked out as an explicit example by means of Feynman diagrams, and this confirms the general argument.
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C. Ofria, T. C. Collier, G. Hsu, and C. Adami
We investigate the evolutionary processes behind the development and optimization of multiple threads of execution in digital organisms using the {\avida} platform, a software package that implements Darwinian evolution on populations of self-replicating computer programs. The system is seeded with a linearly executed ancestor capable only of reproducing its own genome, whereas its underlying language has the capacity for multiple threads of execution (i.e., simultaneous expression of different sections of the genome). We witness the {\it evolution} to multi-threaded organisms and track the development of distinct expression patterns. Additionally, we examine both the evolvability of multi-threaded organisms and the level of thread differentiation as a function of environmental complexity, and find that differentiation is more pronounced in complex landscapes
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C. Adami, C. Ofria, and T.C. Collier
To be added
P.F. Bedaque, H.-W. Hammer, and U. van Kolck
We apply the effective field theory approach to the three-nucleon system. In particular, we consider $S=1/2$ neutron-deuteron scattering and the triton. We show that in this channel a unique nonperturbative renormalization takes place which requires the introduction of a single three-body force at leading order. With one fitted parameter we find a good description of low-energy data. Invariance under the renormalization group explains some universal features of the three-nucleon system ---such as the Thomas and Efimov effects and the Phillips line--- and the origin of $SU(4)$ symmetry in nuclei.
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U. van Kolck
The application of the effective field theory (EFT) method to nuclear systems is reviewed. The roles of degrees of freedom, QCD symmetries, power counting, renormalization, and potentials are discussed. EFTs are constructed for the various energy regimes of relevance in nuclear physics, and are used in systematic expansions to derive nuclear forces in terms of a number of parameters that embody information about QCD dynamics. Two-, three-, and many-nucleon systems, including external probes, are considered
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J.F. Beacom
Core-collapse supernovae emit of order $10^{58}$ neutrinos and antineutrinos of all flavors over several seconds, with average energies of 10--25 MeV. In the Sudbury Neutrino Observatory (SNO), a future Galactic supernova at a distance of 10 kpc would cause several hundred events. The $\nu_\mu$ and $\nu_\tau$ neutrinos and antineutrinos are of particular interest, as a test of the supernova mechanism. In addition, it is possible to measure or limit their masses by their delay (determined from neutral-current events) relative to the $\bar{\nu}_e$ neutrinos (determined from charged-current events). Numerical results are presented for such a future supernova as seen in SNO. Under reasonable assumptions, and in the presence of the expected counting statistics, a $\nu_\mu$ or $\nu_\tau$ mass down to about 30 eV can be simply and robustly determined. This seems to be the best technique for direct measurement of these masses.
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C. Ofria and C. Adami
We examine the evolution of expression patterns and the organization of genetic information in populations of self-replicating digital organisms. Seeding the experiments with a linearly expressed ancestor we witness the development of complex, parallel secondary expression patterns. Using principles from information theory, we demonstrate an evolutionary pressure towards overlapping expressions causing variation (and hence further evolution) to sharply drop. Finally we compare the overlapping sections of dominant genomes to those portions which are singly expressed and observe a significant difference in the entropy of their encoding
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J.F. Beacom and P. Vogel
A future type-II supernova in our Galaxy will be detected by several neutrino detectors around the world. The neutrinos escape from the supernova core over several seconds from the time of collapse, unlike the electromagnetic radiation, emitted from the envelope, which is delayed by a time of order hours. In addition, the electromagnetic radiation can be obscured by dust in the intervening interstellar space. The question therefore arises whether a supernova can be located by its neutrinos alone. The early warning of a supernova and its location might allow greatly improved astronomical observations. The theme of the present work is a careful and realistic assessment of this question, taking into account the statistical significance of the various neutrino signals. Not surprisingly, neutrino-electron forward scattering leads to a good determination of the supernova direction, even in the presence of the large and nearly isotropic background from other reactions. Even with the most pessimstic background assumptions, SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO) can restrict the supernova direction to be within circles of radius $5^\circ$ and $20^\circ$, respectively. Other reactions with more events but weaker angular dependence are much less useful for locating the supernova. Finally, there is the oft-discussed possibility of triangulation, i.e., determination of the supernova direction based on an arrival time delay between different detectors. Given the expected statistics we show that, contrary to previous estimates, this technique does not allow a good determination of the supernova direction.
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J. Chu and C. Adami
Sandpile models have been proposed as the paradigm of certain physical systems which appear to give rise to robust scale-free dynamics without tuning of a parameter. The dynamics involved have been dubbed self-organized criticality (SOC). We show, within a simple mean-field branching process model, that this dynamics is obtained through external tuning of the driving rate and the diffusion rate, and present explicit simulations of sandpiles in the non-critical regime which support this conclusion.
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J. Chu and C. Adami
For taxonomic levels higher than species, the rank-abundance distributions of number of subtaxa per taxon approximate power laws \cite{YULE,BURLANDO1,BURLANDO2}. Yule~\cite{YULE} proposed a continuous time branching process model to explain these distributions at the generic level. He recognized that naturally observed distributions diverged from the power law predicted by his theory for equilibrium distributions, and hypothesized that this deviation was caused by a finite-time effect. Here, we describe a simple branching process that generates the observed distributions and find that the distribution's deviation from power-law form is not caused by disequilibration (as Yule proposed), but rather that it is time-independent and determined by the evolutionary properties of the taxa of interest. Our model predicts---with no free parameters---the rank-frequency distribution of number of families in fossil marine animal orders obtained from the fossil record. We find that near power-law distributions are statistically almost inevitable for taxa higher than species. The branching model also sheds light on species abundance patterns, as well as on links between evolutionary processes, self-organized criticality and fractals
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J. Chu and C. Adami
Scale-free dynamics in physical and biological systems can arise from a variety of causes. Here, we explore a branching process which leads to such dynamics. We find conditions for the appearance of power laws and study quantitatively what happens to these power laws when such conditions are violated. From a branching process model, we predict the behavior of three systems which seem to exhibit near scale-free behavior---rank-frequency distributions of number of subtaxa in biology, abundance distributions of genotypes in an artificial life system, and distributions of avalanche sizes in the Bak-Tang-Wiesenfeld sandpile model
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T.D. Shoppa, S.E. Koonin, and R. Seki
We investigate quantal perturbations of the interferometric correlations of charged bosons by the Coulomb field of an instantaneous, charged source. The source charge increases the apparent source size by weakening the correlation at non-zero relative momenta. The effect is strongest for pairs with a small total momentum and is stronger for kaons than for pions of the same momenta. The experimental data currently available are well described by this effect without invoking Pratt's exploding source model. A simple expression is proposed to account for the effect
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S.R. Beane, M. Malheiro, D.R. Phillips, and U. van Kolck
Compton scattering on the deuteron is studied in the framework of baryon chiral perturbation theory to third order in small momenta, for photon energies of order the pion mass. The scattering amplitude is a sum of one- and two-nucleon mechanisms with no undetermined parameters. Our results are in good agreement with existing experimental data, and a prediction is made for higher-energy data being analyzed at SAL
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U. van Kolck
We discuss renormalization of the non-relativistic three-body problem with short-range forces. The problem is non-perturbative at momenta of the order of the inverse of the two-body scattering length. An infinite number of graphs must be summed, which leads to a cutoff dependence that does not appear in any order in perturbation theory. We argue that this cutoff dependence can be absorbed in one local three-body force counterterm and compute the running of the three-body force with the cutoff. This allows a calculation of the scattering of a particle and the two-particle bound state if the corresponding scattering length is used as input. We also obtain a model-independent relation between binding energy of a shallow three-body bound state and this scattering length. We comment on the power counting that organizes higher-order corrections and on relevance of this result for the effective field theory program in nuclear and molecular physics.
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U. van Kolck
Basic ideas underlying the application of effective field theories to nuclear systems are discussed, and some of their consequences to few-nucleon forces are sketched. Pion photoproduction is used as an illustration of how electromagnetic processes shine light on chiral aspects of nucleon structure and nuclear forces
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Carlos A. da Rocha, Gerald A. Miller and U. van Kolck
Power-counting arguments are used to organize the interactions contributing to the $N N \rightarrow d \pi, pn \pi$ reactions near threshold. We estimate the contributions from the three formally leading mechanisms: the Weinberg-Tomozawa (WT) term, the impulse term, and the $\Delta$-excitation mechanism. Sub-leading but potentially large mechanisms, including $S$-wave pion-rescattering, the Galilean correction to the WT term, and short-ranged contributions are also examined. The WT term is shown to be numerically the largest, and the other contributions are found to approximately cancel. Similarly to the reaction $pp \rightarrow pp\pi^0$, the computed cross sections are considerably smaller than the data. We discuss possible origins of this discrepancy
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P.F. Bedaque, H.-W. Hammer, and U. van Kolck
We discuss renormalization of the non-relativistic three-body problem with short-range forces. The problem becomes non-perturbative at momenta of the order of the inverse of the two-body scattering length, and an infinite number of graphs must be summed. This summation leads to a cutoff dependence that does not appear in any order in perturbation theory. We argue that this cutoff dependence can be absorbed in a single three-body counterterm and compute the running of the three-body force with the cutoff. We comment on relevance of this result for the effective field theory program in nuclear and molecular physics.
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J.C. Astor and C. Adami
We present a model of decentralized growth for Artificial Neural Networks (ANNs) inspired by the development and the physiology of real nervous systems. In this model, each individual artificial neuron is an autonomous unit whose behavior is determined only by the genetic information it harbors and local concentrations of substrates modeled by a simple artificial chemistry. Gene expression is manifested as axon and dendrite growth, cell division and differentiation, substrate production and cell stimulation. We demonstrate the model's power with a hand-written genome that leads to the growth of a simple network which performs classical conditioning. To evolve more complex structures, we implemented a platform-independent, asynchronous, distributed Genetic Algorithm (GA) that allows users to participate in evolutionary experiments via the World Wide Web.
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C. Adami and N.J. Cerf
We suggest that the framework of quantum information theory, which has been developing rapidly in recent years due to intense activity in quantum computation and quantum communication, is a reasonable starting point to study non-equilibrium quantum statistical phenomena. As an application, we discuss the non-equilibrium quantum thermodynamics of black hole formation and evaporation.
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J.F. Beacom and P. Vogel
Core-collapse supernovae emit of order $10^{58}$ neutrinos and antineutrinos of all flavors over several seconds, with average energies of 10--25 MeV. In the Sudbury Neutrino Observatory (SNO), which begins operations this year, neutrinos and antineutrinos of all flavors can be detected by reactions which break up the deuteron. For a future Galactic supernova at a distance of 10 kpc, several hundred events will be observed in SNO. The $\nu_\mu$ and $\nu_\tau$ neutrinos and antineutrinos are of particular interest, as a test of the supernova mechanism. In addition, it is possible to measure or limit their masses by their delay (determined from neutral-current events) relative to the $\bar{\nu}_e$ neutrinos (determined from charged-current events). Numerical results are presented for such a future supernova as seen in SNO. Under reasonable assumptions, and in the presence of the expected counting statistics, a $\nu_\mu$ or $\nu_\tau$ mass down to about 30 eV can be simply and robustly determined. If zero delay is measured, then the mass limit is {\it independent} of the distance $D$. At present, this seems to be the best possibility for direct determination of a $\nu_\mu$ or $\nu_\tau$ mass within the cosmologically interesting range. We also show how to separately study the supernova and neutrino physics, and how changes in the assumed supernova parameters would affect the mass sensitivity.
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J.F. Beacom and P. Vogel
The $\nu_\mu$ and $\nu_\tau$ neutrinos (and their antiparticles) from a Galactic core-collapse supernova can be observed in a water-\v{C}erenkov detector by the neutral-current excitation of $^{16}$O. The number of events expected is several times greater than from neutral-current scattering on electrons. The observation of this signal would be a strong test that these neutrinos are produced in core-collapse supernovae, and with the right characteristics. In this paper, this signal is used as the basis for a technique of neutrino mass determination from a future Galactic supernova. The masses of the $\nu_\mu$ and $\nu_\tau$ neutrinos can either be measured or limited by their delay relative to the $\bar{\nu}_e$ neutrinos. By comparing to the high-statistics $\bar{\nu}_e$ data instead of the theoretical expectation, much of the model dependence is canceled. Numerical results are presented for a future supernova at 10 kpc as seen in the SuperKamiokande detector. Under reasonable assumptions, and in the presence of the expected counting statistics, $\nu_\mu$ and $\nu_\tau$ masses down to about 50 eV can be simply and robustly determined. The signal used here is more sensitive to small neutrino masses than the signal based on neutrino-electron scattering.
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U. Van Kolck
The method of effective field theories (EFTs) is developed for the scattering of two particles at wavelengths which are large compared to the range of their interaction. It is shown that the renormalized EFT is equivalent to the effective range expansion, to a Schr\"odinger equation with a pseudo-potential, and to an energy expansion of a generic boundary condition at the origin. The roles of regulators and potentials are also discussed. These ideas are exemplified in a toy model
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J.L. Friar, D. Huber, and U. Van Kolck
After a brief review of the role three-nucleon forces play in the few-nucleon systems, the chiral-perturbation-theory approach to these forces is discussed. Construction of the (nominal) leading- and subleading-order Born terms and pion-rescattering graphs contributing to two-pion-exchange three-nucleon forces is reviewed, and comparisons are made of the types of such forces that are used today. It is demonstrated that the short-range $c$-term of the Tucson-Melbourne force is unnatural in terms of power counting and should be dropped. The class of two-pion-exchange three-nucleon forces then becomes rather uniform.
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U. Van Kolck
A consistent power counting is developed for theories with short-range interactions
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U. Van Kolck
This is a summary of some of the goals M. Savage, R. Seki and I had in mind for the Workshop. I review the main issues raised in the previous literature, placing the following contributions in context
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S.E. Koonin, E. Kolbe, and M.-C. Chu
We present simulations that explore the connection between earthshine and the earth's albedo. Fluctuations in the earthshine are found to be well-correlated with fluctuations in the global albedo for observations within $90^\circ$ of the new moon. In addition, the average albedo is well-determined from the average terrestrial phase function derived from earthshine observations. These results suggest that precise observations of earthshine will usefully complement satellite-based studies of the earth's reflectivity. The calculated earthshine intensities are also compared with observations.
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N.J. Cerf, L.K. Grover, and C.P. Williams
A quantum algorithm is known that solves an unstructured search problem in a number of iterations of order $\sqrt{d}$, where $d$ is the dimension of the search space, whereas any classical algorithm necessarily scales as $O(d)$. It is shown here that an improved quantum search algorithm can be devised that exploits the structure of a tree search problem by {\em nesting} this standard search algorithm. The number of iterations required to find the solution of an average instance of a constraint satisfaction problem scales as $\sqrt{d^\alpha}$, with a constant $\alpha<1$ depending on the nesting depth and the problem considered. When applying a single nesting level to a problem with constraints of size~2 such as the graph coloring problem, this constant $\alpha$ is estimated to be around~0.62 for average instances of maximum difficulty. This corresponds to a square-root speedup over a classical nested search algorithm, of which our presented algorithm is the quantum counterpart
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N.J. Cerf
A family of asymmetric cloning machines for quantum bits and $N$-dimensional quantum states is introduced. These machines produce two approximate copies of a single quantum state that emerge from two distinct channels. In particular, an asymmetric Pauli cloning machine is defined that makes two imperfect copies of a quantum bit, while the overall input-to-output operation for each copy is a Pauli channel. A no-cloning inequality is derived, characterizing the impossibility of copying imposed by quantum mechanics. If $p$ and $p'$ are the probabilities of the depolarizing channels associated with the two outputs, the domain in $(\sqrt{p},\sqrt{p'})$-space located inside a particular ellipse representing close-to-perfect cloning is forbidden. This ellipse tends to a circle when copying an $N$-dimensional state with $N\to\infty$, which has a simple semi-classical interpretation. The symmetric Pauli cloning machines are then used to provide an upper bound on the quantum capacity of the Pauli channel of probabilities $p_x$, $p_y$ and $p_z$. The capacity is proven to be vanishing if $(\sqrt{p_x},\sqrt{p_y},\sqrt{p_z})$ lies outside an ellipsoid whose pole coincides with the depolarizing channel that underlies the universal cloning machine. Finally, the tradeoff between the quality of the two copies is shown to result from a complementarity akin to Heisenberg uncertainty principle
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C. Adami, R. Seki, and R. Yirdaw
We analyze the geometry of the species-- and genotype-size distribution in evolving and adapting populations of single-stranded self-replicating genomes: here programs in the Avida world. We find that a scale-free distribution (power law) emerges in complex landscapes that achieve a separation of two fundamental time scales: the relaxation time (time for population to return to equilibrium after a perturbation) and the time between mutations that produce fitter genotypes. The latter can be dialed by changing the mutation rate. In the scaling regime, we determine the critical exponent of the distribution of sizes and strengths of avalanches in a system without coevolution, described by first-order phase transitions in single finite niches
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C. Adami and N.J. Cerf
We present a constructive method to translate small quantum circuits into their optical analogues, using linear components of present-day quantum optics technology only. These optical circuits perform precisely the computation that the quantum circuits are designed for, and can thus be used to test the performance of quantum algorithms. The method relies on the representation of several quantum bits by a single photon, and on the implementation of universal quantum gates using simple optical components (beam splitters, phase shifters, etc.). The optical implementation of Brassard et al.'s teleportation circuit, a non-trivial 3-bit quantum computation, is presented as an illustration.
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B. C. Allanach, G. Amelino-Camelia, O. Philipsen, O. Pisanti, and L. Rosa
We analyze the symmetry-breaking patterns of grand unified theories from the point of view of a recently-proposed criterion of renormalization-group naturalness. We perform the analysis on simple non-SUSY SU(5) and SO(10) and SUSY SU(5) GUTs. We find that the naturalness criterion can favor spontaneous-symmetry-breaking in the direction of the smallest of the maximal little groups. Some differences between theories with and without supersymmetry are also emphasized
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N.J. Cerf
A family of quantum cloning machines is introduced that produce two approximate copies from a single quantum bit, while the overall input-to-output operation for each copy is a Pauli channel. A no-cloning inequality is derived, describing the balance between the quality of the two copies. This also provides an upper bound on the quantum capacity of the Pauli channel with probabilities $p_x$, $p_y$ and $p_z$. The capacity is shown to be vanishing if $(\sqrt{p_x},\sqrt{p_y},\sqrt{p_z})$ lies outside an ellipsoid whose pole coincides with the depolarizing channel that underlies the universal cloning machine
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P.F. Bedaque, H.-W. Hammer, and U. van Kolck
We report on results of the effective theory method applied to neutron-deuteron scattering. We extend previous results in the $J=3/2$ channel to non-zero energies and find very good agreement with experiment without any parameter fitting.
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M.-C. Chu, S.M. Ouellette, S. Schramm, and R. Seki
We investigate the temperature dependence of the instanton contents of gluon fields, using unquenched lattice QCD and the cooling method. The instanton size parameter deduced from the correlation function decreases from 0.44fm below the phase-transition temperature $T_c$ ($\approx 150$MeV) to 0.33fm at 1.3 $T_c$. The instanton charge distribution is Poissonian above $T_c$, but it deviates from the convoluted Poisson at low temperature. The topological susceptibility decreases rapidly below $T_c$, showing the apparent restoration of the $U(1)_A$ symmetry already at $T \approx T_c$.
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N.J. Cerf, C. Adami, and R.M. Gingrich
We analyze the properties of the conditional {\em amplitude} operator, the quantum analog of the conditional probability which has been introduced in [quant-ph/9512022]. The spectrum of the conditional operator characterizing a quantum bipartite system is invariant under local unitary transformations and reflects its inseparability. More specifically, it is shown that the conditional amplitude operator of a separable state cannot have an eigenvalue exceeding 1, which results in a necessary condition for separability. This leads us to consider a related separability criterion based on the positive map $\Gamma:\rho \to ({\rm Tr} \rho) - \rho$, where $\rho$ is an Hermitian operator. Any separable state is mapped by the tensor product of this map and the identity into a non-negative operator, which provides a simple necessary condition for separability. In the special case where one subsystem is a quantum bit, $\Gamma$ reduces to time-reversal, so that this separability condition is equivalent to partial transposition. It is therefore also sufficient for $2\times 2$ and $2\times 3$ systems. Finally, a simple connection between this map and complex conjugation in the ``magic'' basis is displayed.
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M.T. Ressell, D.J. Dean, S.E. Koonin, and K. Langanke
We demonstrate the feasibility of realistic Shell Model Monte Carlo (SMMC) calculations spanning multiple major shells, paying particular attention to the center-of-mass motion. We then use this method to study a series of unstable neutron-rich nuclei with active nucleons in both the $sd$ and $pf$ major oscillator shells. In particular, we study nuclei around the two presumed shell closures at $N = 20,28$ and show that SMMC methods can reproduce the measured mass excesses, $B(E2)$'s, and other observables when a suitable nuclear interaction is employed. Our calculations confirm the previously discovered disappearance of the shell gaps for these extremely neutron-rich nuclei. We close with speculations about future applications of multi-shell SMMC calculations.
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N.J. Cerf
In analogy with its classical counterpart, a noisy quantum channel is characterized by a {\it loss}, a quantity that depends on the channel input and on the quantum operation performed by the channel. The loss reflects the quality of the channel: if the loss is zero, {\it quantum} information can be perfectly transmitted at a rate measured by the quantum source entropy. By using block coding based on sequences of $n$ entangled symbols, the {\it average} loss (defined as the overall loss of the joint $n$-symbol channel divided by $n$, when $n\to \infty$) can be made lower than the loss for a single use of the channel. In this context, we examine several upper bounds on the rate at which quantum information can be transmitted reliably via a noisy channel, that is, with an asymptotically vanishing average loss while the {\em one-symbol} loss of the channel is non-zero. These bounds on the channel capacity rely on the entropic Singleton bound on quantum error-correcting codes. Finally, we analyze the Singleton bounds when the noisy quantum channel is supplemented with a classical auxiliary channel.
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S.M. Ouellette and R. Seki
We calculate, in chiral perturbation theory, the change in the self-energy of decuplet baryons in nuclear matter. These self-energy shifts are relevant in studies of meson-nucleus scattering and of neutron stars. Our results are leading order in an expansion in powers of the ratio of characteristic momenta to the chiral symmetry-breaking scale (or the nucleon mass). Included are contact diagrams generated by \mbox{4-baryon} operators, which were neglected in earlier studies for the $\Delta$~isomultiplet but contribute to the self-energy shifts at this order in chiral perturbation theory.
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H. Ito, S.E. Koonin, and R. Seki
Spin-polarization response functions for the high-energy $(\overrightarrow{e},e^{\prime }\overrightarrow{p})$ reaction are examined by computing all 18 response functions for proton kinetic energies of 0.515 and 3.170 GeV from an $^{16}O$ target. The Dirac eikonal formalism is applied to account for the final-state interactions. It is found to yield the response functions in good agreement with those calculated by partial-wave expansion at 0.5 GeV. We identify the response functions that are dominantly determined by the spin-orbit potential in the final-state interaction. Dependence on the Dirac- or Pauli-type current of the nucleon is investigated in the helicity-dependent response functions, and the normal-component polarization of the knocked-out proton is computed.
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N.J. Cerf and S.E. Koonin
The many-body dynamics of a quantum computer can be reduced to the time evolution of non-interacting quantum bits in auxiliary fields by use of the Hubbard-Stratonovich representation of two-bit quantum gates in terms of one-bit gates. This makes it possible to perform the stochastic simulation of a quantum algorithm, based on the Monte Carlo evaluation of an integral of dimension polynomial in the number of quantum bits. As an example, the simulation of the quantum circuit for the Fast Fourier Transform is discussed.
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N.J. Cerf, C. Adami, and P.G. Kwiat
A systematic method for simulating small-scale quantum circuits by use of linear optical devices is presented. It relies on the representation of several quantum bits by a single photon, and on the implementation of universal quantum gates using simple optical components (beams splitters, phase shifters, etc.). This suggests that the optical realization of small quantum networks is reasonable given the present technology in quantum optics, and could be a useful technique for testing simple quantum algorithms or error-correction schemes. The optical circuit for quantum teleportation is presented as an illustration.
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M.T. Ressell and D.J. Dean
We perform nuclear shell model calculations of the neutralino-nucleus cross section for several nuclei in the $A = 127$ region. Each of the four nuclei considered is a primary target in a direct dark matter detection experiment. The calculations are valid for all relevant values of the momentum transfer. Our calculations are performed in the $3s 2d 1g_{7/2} 1h_{11/2}$ model space using extremely large bases, allowing us to include all relevant correlations. We also study the dependence of the nuclear response upon the assumed nuclear Hamiltonian and find it to be small. We find good agreement with the observed magnetic moment as well as other obervables for the four nuclei considered: $^{127}$I, $^{129,131}$Xe, and $^{125}$Te.
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N.J. Cerf and R. Cleve
Quantum error-correcting codes are analyzed from an information-theoretic perspective centered on quantum conditional and mutual entropies. This approach parallels the classical description of coding in Shannon theory, while clarifying the differences between classical and quantum codes. More specifically, it is shown how quantum information theory accounts for the fact that ``redundant'' information can be distributed over quantum bits even though this does not violate the quantum non-cloning theorem. While the quantum bits that are altered appear statistically independent of the encoded logical word for any possible error, the quantum information stored in the entire codeword remains unaffected. This remarkable feature, which has no counterpart in classical coding, is related to the property that the ternary mutual entropy vanishes for a tripartite system in a pure state. These concepts are used to derive the quantum analogue of the Singleton bound on the number of logical bits that can be preserved by a code of fixed length which can recover a given number of errors. Our information-theoretic description of coding also sheds new light on the interpretation of this bound in terms of ``weak'' cloning.
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C. Adami and H.G. Schuster
We show that for a model fitness landscape in which the number of maxima increases exponentially with the molecular length $N$, mutations will drive the evolution of prebiotic molecules to Eigen's error threshold.
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N.J. Cerf and C. Adami
The amount of information that can be accessed via measurement of a quantum system prepared in different states is limited by the Kholevo bound. We present a simple proof of this theorem and its extension to sequential measurements based on the properties of quantum conditional and mutual entropies. The proof relies on a minimal physical model of the measurement which does not assume environmental decoherence, and has an intuitive diagrammatic representation.
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C. Adami and N.J. Cerf
We analyze a quantum channel for information transmission and storage. In analogy to classical channels, we propose to define the quantum channel capacity as the maximum {\em mutual entanglement} processed by the channel (for the transmission and storage of quantum entanglement), which reduces to the maximum {\em mutual information} processed by the channel for the transmission of classical data. The mutual entanglement processed by the channel observes a data-processing inequality, and we derive a quantum Fano inequality relating the {\em loss} of the channel to the fidelity of the quantum code. The existence of error-correcting codes that would saturate our capacity is conjectured. Such ``supercodes'' satisfy an extended ``entanglement'' quantum Hamming bound, distinct from the usual quantum Hamming bound. The mutual entanglement and the capacity are calculated explicitly for the quantum ``depolarizing'' channel.
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N.J. Cerf and C. Adami
We derive entropic Bell inequalities from considering quantum entropy diagrams. These entropic inequalities, akin to the Braunstein-Caves inequalities, are violated for a quantum mechanical Einstein-Podolsky-Rosen pair, which implies that the quantum conditional entropies of the Bell variables must be negative in this case. This suggests that the satisfaction of entropic Bell inequalities is equivalent to the non-negativity of quantum entropies as a necessary condition for separability.
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C. Adami and N.J. Cerf
An investigation of Einstein's ``physical'' reality and the concept of quantum reality in terms of information theory suggests a solution to quantum paradoxes such as the Einstein-Podolsky-Rosen (EPR) and the Schr\"odinger-cat paradoxes. Quantum reality, the picture based on unitarily evolving wavefunctions, is complete, but appears incomplete from the observer's point of view for fundamental reasons arising from the quantum information theory of measurement. Physical reality, the picture based on classically accessible observables is, in the worst case of EPR experiments, unrelated to the quantum reality it purports to reflect. Thus, quantum information theory implies that only correlations, not the correlata, are physically accessible: the mantra of the Ithaca interpretation of quantum mechanics.
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H.-M. Muller and S.E. Koonin
We perform Hartree-Fock calculations to show that quantum dots (i.e. two dimensional systems of up to twenty interacting electrons in an external parabolic potential) undergo a gradual transition to a spin-polarized Wigner crystal with increasing magnetic field strength. The phase diagram and ground state energies have been determined. We tried to improve the ground state of the Wigner crystal by introducing a Jastrow ansatz for the wavefunction and performing a variational Monte Carlo calculation. The existence of so called magic numbers was also investigated. Finally, we also calculated the heat capacity associated with the rotational degree of freedom of deformed many-body states
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R.D. McKeown
The strange magnetic moment of the nucleon ($\mu_s$) is examined as part of the nucleon's isoscalar anomalous moment. The dominant up and down quark effects in the anomalous moment may actually tend to favor $\mu_s >0$, which is contrary to the negative values that generally result from model calculations. The possible origins of this apparent discrepancy are considered
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K. Langanke
In recent years astrophysical applications have been the driving force for much research in nuclear physics. Very often these problems involve rather evolved many-body physics. In many cases mean-field approaches are the first method of choice. But often more elaborate models which take proper account of nucleonic correlations beyond the mean-field level are called for. The interacting shell model \cite{Haxel} is generally considered to be the most fundamental theory of the nucleus short of an explicit solution of the $A$-body problem. This paper will discuss several astrophysical scenarios in which recently shell model calculations have significantly contributed to a better theoretical understanding. But it will also focus on important astrophysical problems and recent developments in which the nuclear many-body problem is yet treated on the mean-field level or within the many-body theory of small-amplitude vibrations, the random phase approximation. These applications can be viewed as a motivation for potential future shell model calculations. In particular the paper discusses three different astrophysical scenarios which are all currently drawing strong research interest. At first we will review the solar neutrino problem, with special emphasis on the fate of the $^7$Be neutrinos and the attempts of their earthbound observations. In the second part we discuss some topics important during the presupernova collapse. Particular progress has been achieved recently in the calculation of electron capture rates for the relevant nuclei in the iron-mass region and in the description of nuclei at finite temperature. The final topic deals with neutrino-nucleus interactions and their role in various aspects of the supernova, including a possible detection scheme for $\mu$- and $\tau$-neutrinos in water Cerenkov detectors like Superkamiokande.
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J. Engel, E. Kolbe, K. Langanke, and P. Vogel
Neutrino induced reactions on $^{12}$C, an ingredient of liquid scintillators, have been studied in several experiments. We show that for currently available neutrino energies, $E_{\nu} \le$ 300 MeV, calculated exclusive cross sections $^{12}$C$_{gs}(\nu,l)$$^{12}$N$_{gs}$ for both muon and electron neutrinos are essentially model independent, provided the calculations simultaneously describe the rates of several other reactions involving the same states or their isobar analogs. The calculations agree well with the measured cross sections, which can be therefore used to check the normalization of the incident neutrino spectrum and the efficiency of the detector.
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N.J. Cerf and C. Adami
We present a quantum information theory that allows for the consistent description of quantum entanglement. It parallels classical (Shannon) information theory but is based entirely on matrices, rather than probability distributions, for the description of quantum ensembles. We find that conditional quantum entropies can be negative for quantum entangled systems, which leads to a violation of well-known bounds in classical information theory. Such a treatment clarifies the link between classical correlation and quantum entanglement: the latter can be understood as ``super-correlation'' which can induce classical correlation, while the reverse is impossible. Furthermore, negative entropy and the associated clarification of entanglement paves the way to a natural, unitary, and causal model of the measurement process, while implying all the well-known results of conventional probabilistic quantum mechanics.
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N.J. Cerf and C. Adami
We show that the recent discovery of negative (conditional) quantum entropy reveals that measurement in quantum mechanics is not accompanied by the collapse of a wavefunction or a quantum jump. Rather, quantum measurement appears as a sequence of unitary operations which are reversible in principle, although ususally not in practice. The probabilistic nature of quantum measurement emerges from the positive entropy of the observed subsystem, which however is exactly cancelled by the negative entropy of the remaining (unobserved) part. Thence, the entropy of the combined system is unchanged while measurement itself is probabilistic. In this framework, uncertainty relations which characterize the measurement of incompatible variables emerge naturally, as do all well-known relations of conventional quantum mechanics. Yet, quantum measurement is unitary, causal, and free of any {\em ad hoc} assumptions. We apply this theory to standard quantum measurement situations such as the Stern-Gerlach and double-slit experiments to illustrate how randomness, inherent in the conventional quantum probabilities, arises in a unitary framework. Finally, the present view clarifies the relationship beween classical and quantum concepts.
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C. Adami and N.J. Cerf
We consider the duality between computation and measurement emerging from the thermodynamics of Turing machines. This duality suggests a new measure of complexity (physical complexity) which corresponds to our intuition and appears to be practical enough to estimate the complexity of genomes. From an automata theoretic point of view, this complexity is just the mutual information between a thermodynamic Turing machine and the equilibrated tape that constitutes its ``universe''. By the same token, the complexity is dual to the mutual entropy between the observer and the system in the information theory of measurement. The complexity of a bit-string, therefore, is the number of bits that can be used to lower the entropy of a closed system. Random strings have vanishing physical complexity (even though they have maximal Kolmogorov complexity), as they cannot be the result of a (classical) measurement or computation.
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J. Chu and C. Adami
We observe the propagation of information in a system of self-replicating strings of code (``Artificial Life'') as a function of fitness and mutation rate. Comparison with theoretical predictions based on the reaction-diffusion equation shows that the response of the artificial system to fluctuations (\eg velocity of the information wave as a function of relative fitness) closely follows that of natural systems. We find that the relaxation time of the system depends on the speed of propagation of information and the size of the system. This analysis offers the possibility of determining the minimal system size for observation of non-equilibrium effects at fixed mutation rate.
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S.E. Koonin, D.J. Dean, and K. Langanke
We review quantum Monte Carlo methods for dealing with large shell model problems. These methods reduce the imaginary-time many-body evolution operator to a coherent superposition of one-body evolutions in fluctuating one-body fields; the resultant path integral is evaluated stochastically. We first discuss the motivation, formalism, and implementation of such Shell Model Monte Carlo (SMMC) methods. There then follows a sampler of results and insights obtained from a number of applications. These include the ground state and thermal properties of {\it pf}-shell nuclei, the thermal and rotational behavior of rare-earth and $\gamma$-soft nuclei, and the calculation of double beta-decay matrix elements. Finally, prospects for further progress in such calculations are discussed.
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K. Langanke, D.J. Dean, P.B. Radha, and S.E. Koonin
We use the shell model Monte Carlo approach to study thermal properties and pair correlations in $^{54,56,58}$Fe and in $^{56}$Cr. The calculations are performed with the modified Kuo-Brown interaction in the complete $1p0f$ model space. We find generally that the proton-proton and neutron-neutron $J=0$ pairing correlations, which dominate the ground state properties of even-even nuclei, vanish at temperatures around 1 MeV. This pairing phase transition is accompanied by a rapid increase in the moment of inertia and a partial unquenching of the M1 strength. We find that the M1 strength totally unquenches at higher temperatures, related to the vanishing of isoscalar proton-neutron correlations, which persist to higher temperatures than the pairing between like nucleons. The Gamow-Teller strength is also correlated to the isoscalar proton-neutron pairing and hence also unquenches at a temperature larger than that of the pairing phase transition.
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T.D. Shoppa, M. Jeng, S.E. Koonin, K. Langanke, and R. Seki
Recent laboratory experiments have measured fusion cross sections at center-of-mass energies low enough for the effects of atomic and molecular electrons to be important. To extract the cross section for bare nuclei from these data (as required for astrophysical applications), it is necessary to understand these screening effects. We study electron screening effects in the low-energy collisions of $Z=1$ nuclei with hydrogen molecules. Our model is based on a dynamical evolution of the electron wavefunctions within the TDHF scheme, while the motion of the nuclei is treated classically. We find that at the currently accessible energies the screening effects depend strongly on the molecular orientation. The screening is found to be larger for molecular targets than for atomic targets, due to the reflection symmetry in the latter. The results agree fairly well with data measured for deuteron collisions on molecular deuterium and tritium targets.
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N.J. Cerf
We present a novel quantum Monte Carlo method based on a path integral in Fock space, which allows to compute finite-temperature properties of a many-body nuclear system with a monopole pairing interaction in the canonical ensemble. It enables an exact calculation of the thermodynamic variables such as the internal energy, the entropy, or the specific heat, from the measured moments of the number of hops in a path of nuclear configurations. Monte Carlo calculations for a single-shell $(h_{11/2})^6$ model % with a constant pairing strength % show an inflection point in the internal energy or equivalently % show a peak in the specific heat % near a temperature of 2~MeV, that is associated with % exhibit the vanishing of nucleon pair correlations % near a temperature of 2~MeV, and are consistent with an exact calculation from the many-body spectrum in the seniority model.
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N.J. Cerf and C. Adami
We describe a consistent framework for information theory in quantum mechanics. Unlike in classical (Shannon) information theory, conditional entropies can be negative when considering quantum entangled systems. This has the remarkable consequence that negative virtual information can be carried by particles. Accordingly, quantum informational processes can be described by diagrams, much like particle physics reactions, involving quantum bits and antibits. This allows us to reinterpret quantum teleportation and superdense coding in a fully consistent way.
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M.T. Ressell, G.J. Mathews, M.B. Aufderheide, S.D. Bloom, and D.A. Resler
We examine the effects on the nuclear neutral current Gamow-Teller (GT) strength of a finite contribution from a polarized strange quark sea. We perform nuclear shell model calculations of the neutral current GT strength for a number of nuclei likely to be present during stellar core collapse. We compare the GT strength when a finite strange quark contribution is included to the strength without such a contribution. As an example, the process of neutral current nuclear de-excitation via $\nu {\overline{\nu}}$ pair production is examined for the two cases.
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M.T. Ressell, J. Engel, and P. Vogel
We use the experimental limit on the interference of M1 and E2 multipoles in the $\gamma$-decay of $^{57}$Fe to bound the time-reversal-violating parity-conserving $\rho N N$ vertex. Our approach is a large-basis shell-model calculation of the interference. We find an upper limit on the parameter $\bar{g}_{\rho}$, the relative strength of the T-violating $\rho N N$ vertex, of close to $10^{-2}$, a value similar to the best limits from other kinds of experiments.
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R. Seki, T.D. Shoppa, A. Kohama, and K. Yazaki
Nuclear transparency is calculated for high-energy, semi-inclusive $(e,e'p)$ reactions, by accounting for all orders of Glauber multiple-scattering and by using realistic finite-range $p N$ interaction and (dynamically and statistically) correlated nuclear wave functions. The nuclear correlation effect is reduced due to the $p N$ finite-range effect. %Furthermore, the short- and medium-range %correlations change the transparency in opposite ways. The net effect is small, and depends sensitively on details of the nuclear correlations in finite nuclei, which are poorly known at present.
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K. Langanke, P. Vogel, and E. Kolbe
We suggest that photons with energies between 5 and 10 MeV, generated by the ($\nu,\nu'p\gamma$) and ($\nu,\nu'n\gamma$) reactions on $^{16}$O, constitute a signal which allows a unique identification of supernova $\nu_\mu$ and $\nu_\tau$ neutrinos in water \v{C}erenkov detectors. We calculate the yield of such $\gamma$ events and estimate that a few hundred of them would be detected in Superkamiokande for a supernova at 10 kpc distance.
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K. Langanke, T. D. Shoppa, C. A. Barnes, and C. Rolfs
We reanalyze the low-energy $^3$He(d,p)$^4$He cross section measurements of Engstler {\it et al.} using recently measured energy loss data for proton and deuteron beams in a helium gas. Although the new $^3$He(d,p)$^4$He S-factors are significantly lower than those reported by Engstler {\it et al.}, they clearly show the presence of electron screening effects. >From the new S-factors we find an electron screening energy in agreement with the adiabatic limit.
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D. J. Dean, S. E. Koonin, T. T. S. Kuo, K. Langanke, and P. B. Radha
We perform shell model Monte Carlo calculations for nuclei in the $^{100}$Sn region within the complete $0g$-$1d$-$2s$ oscillator shell using an effective interaction derived from the Paris nucleon-nucleon potential. We find good agreement with empirically calculated masses, and reproduce the observed quenching of the total Gamow-Teller strengths in this mass region. The Gamow-Teller strength in $^{100}$Sn is predicted to be nearly a factor of 3 smaller than the single particle estimate.
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P. B. Radha, D. J. Dean, S. E. Koonin, T. T. S. Kuo, K. Langanke, A. Poves, J. Retamosa, and P. Vogel
Shell Model Monte Carlo (SMMC) techniques are used to calculate two-neutrino double beta decay matrix elements. We test the approach against direct diagonalization for $^{48}$Ca in the complete $pf$-shell using the KB3 interaction. The method is then applied to the decay of $^{76}$Ge in the $(0f_{5/2},1p,0g_{9/2})$ model space using a newly calculated realistic interaction. Our result for the matrix element is $0.12\pm0.05$ MeV$^{-1}$, in reasonable agreement with the experimental value.
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S. E. Koonin
Quantum Monte Carlo methods find fruitful application in large shell model problems. These methods reduce the imaginary-time many-body evolution operator to a coherent superposition of one-body evolutions in a fluctuating one-body field; the resultant path integral is evaluated stochastically. After a brief review of the capabilities and general strategy of Shell Model Monte Carlo methods, I discuss results and insights obtained from a number of applications. These include the ground state and thermal properties of {\nineit pf}-shell nuclei, the thermal and rotational behavior of rare-earth and $\gamma$-soft nuclei, and the calculation of double beta-decay matrix elements. Prospects for further progress in such calculations are also discussed.
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A. Poves, R. Bahukutumbi, K. Langanke, and P. Vogel
The $^{48}$Ca$\rightarrow ^{48}$Ti two neutrino double-beta decay rate is calculated exactly in the full $fp$ shell with the hamiltonian describing well the spectroscopy of the $A$=48 system. The resulting half-life is very near the experimental lower limit. In order to find out whether the shell model can at all accommodate longer $2\nu$ half-lives we modify the hamiltonian in several ways, keeping, however, the acceptable agreement with the main spectroscopic indicators intact. We conclude that, within such an approach, the longest possible half-life is about 10$^{20}$ years, only a factor of three longer than the present limit. We stress that any possible modifications of the hamiltonian must be restricted by the comparison with available data on energy levels and transitions rates.
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E. Kolbe, K. Langanke, F.-K. Thielemann, and P. Vogel
Motivated by a recent experiment at LAMPF, we calculate cross sections for muon-neutrino and muon-antineutrino charged-current reactions on $^{12}$C within the Continuum RPA model. We also determine the branching ratios for the main decay channels of these reactions by application of a statistical model.
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H. A. Bethe and G. E. Brown
We review estimates of the mass of the compact core in SN1987A and conclude that the most accurate determination can be obtained from the known ~0.075 M_dot of Ni production in the explosion. With binding energy correction, this gives an upper limit of gravitational mass 1.56 M_dot, slightly larger than the Brown and Bethe (1994) estimate of ~1.5 M_dot. Observation by OSSE of the ratio of gamma-rays from Co57 and Co56 indicates that neutron rich material from the inner regions does not reach the mass cut by convection or Rayleigh-Taylor instability. Arguments that the core of SN1987A went into a black hole are reviewed. If one accepts this to be true, then the maximum compact core mass gives an upper limit on neutron star masses max(M_NS) ~= 1.56M_dot (gravitational) in rough agreement with Brown and Bethe (1994).
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M. R. Haggerty
The efficacy and accuracy of Bogomolny's method of the quantum surface of section is evaluated by applying it to the quantization of the motion of a particle in a smooth 2-D potential. This method defines a transfer operator T in terms of classical trajectories of one Poincare crossing; knowledge of T provides information about the eigenstates of the quantum system. By using a more robust quantization criterion than the one proposed by Bogomolny, we are able to locate more than five hundred quantum states in both the regular and the chaotic regimes---in most cases unambiguously---and see no reason that the spectra could not be continued indefinitely. The errors of the predictions are comparable in the two regimes, and roughly constant for increasing excitation, but grow as a fraction of the (shrinking) mean level spacing. We also show computed surface of section wavefunctions, and present other theoretical and practical results related to the technique.
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M.-C. Chu and S. Schramm
We investigate the temperature dependence of the instanton content of gluon fields and their contribution to quark correlation using quenched lattice QCD and the cooling method. We found a suppression of the topological susceptibility at finite temperature, agreeing with the PCAC expectation at low temperature and enhanced suppression for temperatures at and above the deconfinement transition. For temperatures up to about 334 MeV, the topological charge correlation agrees well with a single instanton profile, though the size parameter seems to change across the phase transition. The screening wave functions for the pion and the rho become slightly more compact at higher temperatures. Lattice cooling shows no contribution from the instantons to the screening wave functions at temperatures above the phase transition.
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D. J. Dean, S.E. Koonin, K. Langanke, and P.B. Radha
We have studied the properties of A=54 and A=64 isobars at temperatures T <= 2 MeV via Monte Carlo shell model calculations with two different residual interactions. In accord with empirical indications, we find that the symmetry energy coefficient, b_sym, is independent of temperature to within 0.6 MeV for T <= 1 MeV. This is in contrast to a recent suggestion of a 2.5 MeV increase of b_sym for this temperature, which would have significantly altered the supernova explosion scenario.
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A. Csoto, K. Langanke, S.E. Koonin, and T.D. Shoppa
We study the nonresonant part of the 7 Be(p,\gamma) 8 B reaction using a three-cluster resonating group model that is variationally converged and virtually complete in the 4 He + 3 He + p model space. The importance of using adequate nucleon-nucleon interaction is demonstrated. We find that the low-energy astrophysical S-factor is linearly correlated with the quadrupole moment of 7 Be. A range of parameters is found where the most important 7 Be and 7 Li properties are reproduced simultaneously; the corresponding S-factor at E_cm=20 keV is 24.6-26.1 eV.
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M.C. Chu, S. Gardner, T. Matsui, and R. Seki
An extended pion source, which can be temporarily created by a high energy nuclear collision, will also absorb and distort the outgoing pions. We discuss how this effect alters the interferometric pattern of the two-pion momentum correlation function. In particular, we show that the two-pion correlation function decreases rapidly when the opening angle between the pions increases. The opening-angle dependence should serve as a new means of obtaining information about the pion source in the analysis of experimental data.
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E. Kolbe, K. Langanke, and P. Vogel
We use the continuum random phase approximation to describe the muon capture on 12 C, 16 O and 40 Ca. We reproduce the experimental total capture rates on these nuclei to better than 10% using the free nucleon weak form factors and two different residual interactions. However, the calculated rates for the same residual interactions are significantly lower than the data if the in-medium quenching of the axial-vector coupling constant is employed.
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C. Adami and C.T. Brown
We present a new tierra-inspired artificial life system with local interactions and two-dimensional geometry, based on an update mechanism akin to that of 2D cellular automata. We find that the spatial geometry is conducive to the development of diversity and thus improves adaptive capabilities. We also demonstrate the adaptive strength of the system by breeding cells with simple computational abilities, and study the dependence of this adaptibility on mutation rate and population size.
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C. Adami
We present a theoretical as well as experimental investigation of a population of self-replicating segments of code subject to random mutation and survival of the fittest. Under the assumption that such a system constitutes a minimal system with characteristics of life, we obtain a number of statements on the evolution of complexity and the trade-off between entropy and information.
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D. J. Dean, S. E. Koonin, K. Langanke, P.B. Radha, and Y. Alhassid
We use Monte Carlo methods to study the thermal properties of Fe54 with the Brown-Richter interaction in the complete 1p0f model space. A rapid increase in the moment of inertia and a peak in the heat capacity near a temperature of 1.2 MeV correlate with the vanishing of the proton-proton and neutron-neutron monopole pair correlations; neutron-proton pairing persists to temperatures above 1.8 MeV. The density of states for excitation energies between 4.5 and 15 MeV is described by a Fermi gas parameter a=7.7 +/- 1.3 MeV^-1, in accord with experiment.
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A. Csoto
Using the complex scaling method, the low-lying three-body resonances of He-6, Li-6, and Be-6 are investigated in a parameter-free microscopic three-cluster model. In He-6 a 2+, in Li-6 a 2+ and a 1+, and in Be-6 the 0+ ground state and a 2+ excited state is found. The other experimentally known 2+ state of Li-6 cannot be localized by our present method. We have found no indication for the existence of the predicted 1- soft dipole state in $^6$He. We argue that the sequential decay mode of He-6 through the resonant states of its two-body subsystem can lead to peaks in the excitation function. This process can explain the experimental results in the case of Li-11, too. We propose an experimental analysis, which can decide between the soft dipole mode and the sequential decay mode.
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D. J. Dean, P. B. Radha, K. Langanke, Y. Alhassid, S. E. Koonin, and W. E. Ormand
Gamow-Teller strengths for selected nuclei in the iron region (A~56) have been investigated via shell-model Monte Carlo calculations with realistic interactions in the complete fp basis. Results for all cases show significant quenching relative to single-particle estimates, in quantitative agreement with (n,p) data. The J=1,T=0 residual interaction and the f_{7/2}-f_{5/2} spin-orbit splitting are shown to play major roles in the quenching mechanism. Calculated B(E2, 2^+_1 -> 0^+_1) values are in fair agreement with experiment using effective charges of e_p=1.1e and e_n=0.1e.
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K. Langanke and T. D. Shoppa
We have calculated the E1 and E2 contributions to the low-energy B-8 + Pb-208 -> p + Be-7 + Pb-208 Coulomb dissociation cross sections using the kinematics of a recent experiment at RIKEN. Using a potential model description of the Be-7 (p,gamma) B-8 reaction, we find that the E2 contributions cannot a priori be ignored in the analysis of the data. Its inclusion reduces the extracted Be-7 (p,gamma) B-8 S-factor at solar energies by about 25%.
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C. Adami
We suggest that ensembles of self-replicating entities such as biological systems naturally evolve into a self-organized critical state in which fluctuations, as well as waiting times between phase transitions ("epochs"), are distributed according to a 1/f power law. We demonstrate these concepts by analyzing a population of coexisting self-replicating strings (segments of computer code) subject to mutation and survival of the fittest.
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S. E. Koonin and K. Langanke
We show that the presently available data on the Gamow-Teller (GT) strength in mid-fp-shell nuclei are proportional to the product of the numbers of valence protons and neutron holes in the full fp-shell. This observation leads to important insights into the mechanism for GT quenching and to a simple parametrization of the Gamow-Teller strengths important for electron capture by fp-shell nuclei in the early stage of supernovae.
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A. Csoto
It is demonstrated that the complex scaling method can be used in practical calculations to localize three-body resonances. Our model example emphasizes the fact that in three-body systems several essentially different asymptotic behaviors can appear. We show that the possibility of these different asymptotic configurations can lead to an apparent, resonance like structure in the three-body continuum.
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C. Adami
We describe and investigate the learning capabilities displayed by a population of self-replicating segments of computer code subject to random mutation: the tierra environment. We find that learning is achieved through phase transitions that adapt the population to whichever environment it encounters, with a learning rate characterized by the environmental variables. Our results suggest that most effective learning is achieved close to the edge of chaos.
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D. J. Dean, S. E. Koonin, G. H. Lang, P. B. Radha, and W. E. Ormand
We present the first auxiliary field Monte Carlo calculations for a rare earth nucleus, 170-Dy. A pairing plus quadrupole Hamiltonian is used to demonstrate the physical properties that can be studied in this region. We calculate various static observables for both uncranked and cranked systems and show how the shape distribution evolves with temperature. We also introduce a discretization of the path integral that allows a more efficient Monte Carlo sampling.
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Y. Alhassid, D. J. Dean, S. E. Koonin, G. H. Lang, and W. E. Ormand
We present a practical solution to the "sign problem" in the auxiliary field Monte Carlo approach to the nuclear shell model. The method is based on extrapolation from a continuous family of problem-free Hamiltonians. To demonstrate the resultant ability to treat large shell-model problems, we present results for Fe54 in the full fp-shell basis using the Brown-Richter interaction. We find the Gamow-Teller beta+ strength to be quenched by 58% relative to the single-particle estimate, in better agreement with experiment than previous estimates based on truncated bases.
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E. Kolbe, K. Langanke, and S. Krewald
Motivated by recent experiments we have studied nu_e and nu_mu induced charged- and neutral-current reactions on 12-C within the continuum random phase approximation employing two different residual interactions. We find good agreement with the measured cross sections for the nu_e-reactions, while our calculation significantly differs from recently measured nu_mu cross sections. Our calculation indicates that the measurements of the total 12-C(nu_e,e^-)12-N* cross sections are consistent with the total 12-C(mu,nu_mu)12-B* capture rate.
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W. E. Ormand, D. J. Dean, C. W. Johnson, G. H. Lang, and S. E. Koonin
We apply the auxiliary-field Monte Carlo approach to the nuclear shell model in the 1s-0d configuration space. The Hamiltonian was chosen to have isovector pairing and isoscalar multipole-multipole interactions, and the calculations were performed within the fixed-particle, canonical ensemble. The results demonstrate the feasibility of the method for N\neq Z even-even and odd-odd N=Z nuclei. In particular, static observables for even-even Ne isotopes and 22-Na compare well with results obtained from exact diagonalization of the Hamiltonian. Response functions are presented for 22-Ne and compared with exact results, and the viability of cranked calculations for N\neq Z even-even nuclei is addressed. We present methods for computing observables in the canonical ensemble using Fourier extraction, and for determining the nuclear shape.
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