Role of heavy meson exchange in near threshold NN-->d pi.

title: Equation of state of dense matter from a density dependent relativistic mean field model
abstract: 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

title: Semiclassical quark model of the nuclear matter response
abstract: 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.

title: Breaking strain of neutron star crust and gravitational waves.
abstract: 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.

title: Role of heavy-meson exchange in pion production near threshold.
abstract: 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

title: Structure of accreted neutron star crust
abstract: 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.

title: New exact solutions for the purely cubic bosonic string field theory.
abstract: A procedure is described for obtaining new exact solutions for the purely cubic form of Witten's bosonic string field theory. These solutions do not correspond to conformally invariant $\ensuremath{\sigma}$ models. Some of them have no tachyons in their spectrum of linearized fluctuations (but may have negative-norm states). Others make no reference to a space-time metric.

title: Cosmic censorship and the dilaton.
abstract: 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.

title: Exact solutions and singularities in string theory.
abstract: We construct two new classes of exact solutions to string theory which are not of the standard plane wave of gauged WZW type. Many of these solutions have curvature singularities. The first class includes the fundamental string solution, for which the string coupling vanishes near the singularity. This suggests that the singularity may not be removed by quantum corrections. The second class consists of hybrids of plane wave and gauged WZW solutions. We discuss a four-dimensional example in detail.

title: Quantum cosmology with a positive-definite action.
abstract: We argue that the indefiniteness of the Euclidean Einstein action is more serious in the cosmological context than in the asymptotically Euclidean context. To correct this, we consider a positive-definite action containing quadratic curvature terms. The physical states \ensuremath{\Psi} are now functions of both a three-metric ${q}_{\mathrm{ab}}$ and extrinsic curvature ${K}_{\mathrm{ab}}$, and satisfy a differential equation analogous to the Wheeler-DeWitt equation. This equation has the form of a Schr\"odinger equation with ${q}_{\mathrm{ab}}$ playing the role of ``time.'' By adopting Hartle and Hawking's boundary condition on the Euclidean function integral, we obtain a ``preferred'' solution to this equation. It is shown that in a simple minisuperspace model this wave function describes an inflationary universe.

title: Statistical Entropy of Nonextremal Four-Dimensional Black Holes and U-Duality.
abstract: 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.