13946091
Detection of atmospheric neutrinos and relativistic nuclear structure effects.
Neutrino-nucleus cross sections for the detection of atmospheric neutrinos are calculated in relativistic impulse and random phase approximations. Pion production is estimated via inclusive {Delta}-hole nuclear excitations. The number of pion events can confuse the identification of the neutrino flavor. As a further source of pions we calculate coherent pion production (where the nucleus remains in the ground state). We examine how these nuclear structure effects influence atmospheric neutrino experiments and study possible improvements in the present detector simulations. {copyright} {ital 1996 The American Physical Society.}
7349001
Semiclassical quark model of the nuclear matter response
The longitudinal response function R(q,w) of nuclear matter is calculated in a semiclassical quark model. The model has a many‐body string‐flip potential that confines quarks into hadrons and avoids color van der Waals forces. Molecular dynamics simulations are used to calculate R(q,w) in one space dimension for a variety of momentum transfers q and excitation energies w. The response function decreases with density (compared to a free hadron response) because of quark exchange between hadrons. © 1995 American Institute of Physics.
15216981
Role of heavy-meson exchange in pion production near threshold.
Recent calculations of s-wave pion production have severely underestimated the accurately known pp → pp� 0 total cross section near threshold. In these calculations, only the single-nucleon axial-charge operator is considered. We have calculated, in addition to the one-body term, the two-body contributions to this reaction that arise from the exchange of mesons. We find that the inclusion of the scalar �-meson exchange current (and lesser contributions from other mesons) increases the cross section by about a factor of five, and leads to excellent agreement with the data. The results are neither very sensitive to changes in the distorting potential that generates the NN wave function, nor to different choices for the meson-nucleon form factors. We argue that pp → pp� 0 data provide direct experimental evidence for meson
28173455
Breaking strain of neutron star crust and gravitational waves.
Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of the neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Because of the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gravitational wave radiation could limit the spin periods of some stars and might be detectable in large-scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in magnetar giant flares and microflares.
119115588
Structure of accreted neutron star crust
Using molecular dynamics simulations, we determine the structure of neutron star crust made of rapid proton capture nucleosynthesis material. We find a regular body-centered cubic lattice, even with the large number of impurities that are present. Low-charge-Z impurities tend to occupy interstitial positions, while high-Z impurities tend to occupy substitutional lattice sites. We find strong attractive correlations between low-Z impurities that could significantly increase the rate of pycnonuclear (density driven) nuclear reactions. The thermal conductivity is significantly reduced by electron impurity scattering. Our results will be used in future work to study the effects of impurities on mechanical properties such as the shear modulus and breaking strain.
119109148
Equation of state of dense matter from a density dependent relativistic mean field model
We calculate the equation of state (EOS) of dense matter using a relativistic mean field (RMF) model with a density dependent coupling that is a slightly modified form of the original NL3 interaction. For nonuniform nuclear matter we approximate the unit lattice as a spherical Wigner-Seitz cell, wherein the meson mean fields and nucleon Dirac wave functions are solved fully self-consistently. We also calculate uniform nuclear matter for a wide range of temperatures, densities, and proton fractions, and match them to nonuniform matter as the density decreases. The calculations took over 6000 CPU days in Indiana University's supercomputer clusters. We tabulate the resulting EOS at over 107,000 grid points in the proton fraction range Y{sub P}=0 to 0.56. For the temperature range T=0.16 to 15.8 MeV, we cover the density range n{sub B}=10{sup -4} to 1.6 fm{sup -3}; and for the higher temperature range T=15.8 to 80 MeV, we cover the larger density range n{sub B}=10{sup -8} to 1.6 fm{sup -3}. In the future we plan to study low density, low temperature (T<15.8 MeV), nuclear matter using a Virial expansion, and we will match the low-density and high-density results to generate a complete EOS table for use in astrophysical simulationsmore » of supernova and neutron star mergers.« less
633266
Counting States of Near-Extremal Black Holes.
A six-dimensional black string is considered and its Bekenstein-Hawking entropy computed. It is shown that to leading order above extremality this entropy precisely counts the number of string states with the given energy and charges. This identification implies that Hawking decay of the near-extremal black string can be analyzed in string perturbation theory and is perturbatively unitary.
43551044
Extremal black holes as exact string solutions.
We show that the leading order solution describing an extremal electrically charged black hole in string theory is, in fact, an exact solution to all orders in [alpha][prime] when interpreted in a Kaluza-Klein fashion. This follows from the observation that it can be obtained via dimensional reduction from a five-dimensional background which is proved to be an exact string solution.
16978340
Cosmic censorship and the dilaton.
We investigate extremal electrically charged black holes in Einstein-Maxwell-dilaton theory with a cosmological constant inspired by string theory. These solutions are not static, and a timelike singularity eventually appears which is not surrounded by an event horizon. This suggests that cosmic censorship may be violated in this theory.
13557911
Breaking cosmic strings without monopoles.
It is shown that topologically stable cosmic strings can, in fact, appear to end or to break, even in theories without monopoles. This can occur whenever the spatial topology of the universe is nontrivial. For the case of Abelian-Higgs strings, we describe the gauge and scalar field configurations necessary for a string to end on a black hole. We give a lower bound for the rate at which a cosmic string will break via black hole pair production, using an instanton calculation based on the Euclidean C-metric.
1606973
Statistical Entropy of Nonextremal Four-Dimensional Black Holes and U-Duality.
We identify the states in string theory which are responsible for the entropy of near-extremal rotating four-dimensional black holes in {ital N}=8 supergravity. For black holes far from extremality (with no rotation), the Bekenstein-Hawking entropy is exactly matched by a mysterious duality invariant extension of the formulas derived for near-extremal black holes states. {copyright} {ital 1996 The American Physical Society.}