Search

We study the charged and neutral current weak interaction rates relevant for the determination of neutrino opacities in dense matter found in supernovae and neutron stars. We establish an efficient formalism for calculating differential cross sections and mean free paths for interacting, asymmetric nuclear matter at arbitrary degeneracy. The formalism is valid for both charged and neutral current reactions. Strong interaction corrections are incorporated through the in-medium single particle energies at the relevant density and temperature. The effects of strong interactions on the weak interaction rates are investigated using both potential and effective field-theoretical models of matter. We investigate the relative importance of charged and neutral currents for different astrophysical situations, and also examine the influence of strangeness-bearing hyperons. Our findings show that the mean free paths are significantly altered by the effects of strong interactions and the multi-component nature of dense matter. The opacities are then discussed in the context of the evolution of the core of a protoneutron star., 41 pages, 25 figures

The equation of state (EOS) is an essential physical ingredient in simulations of gravitational collapse, supernovae, old and newly born neutron stars, and binary mergers of compact stars. In this talk, I will examine (1) the extent to which stringent constraints may be placed on the EOS by a comparison of calculations with the available data on some basic neutron star properties; and (2) some astrophysical consequences of the possible presence of strangeness, in the form of baryons, notably the Λ and Σ−, or as a Bose condensate, such as a K− meson condensate, or in the form of strange quarks.

We study relativistic S+Au collisions at 200 A GeV/c using a hydrodynamical approach. We test various equations of state (EOSs), which are used to describe the strongly interacting matter at densities attainable in the CERN-SPS heavy ion experiments. For each EOS, suitable initial conditions can be determined to reproduce the experimental hadron spectra; this emphasizes the ambiguity between the initial conditions and the EOS in such an approach. Simultaneously, we calculate the resulting thermal photon and dielectron spectra, and compare with experiments. If one allows the excitation of resonance states with increasing temperature, the electro-magnetic signals from scenarios with and without phase transition are very similar and are not resolvable within the current experimental resolution. With regard to the CERES dilepton data, none of the EOSs considered, in conjunction with the standard leading order dilepton rates, succeed in reproducing the observed excess of dileptons below the rho peak. Our work, however, suggests that an improved measurement of the photon and dilepton spectra has the potential to strongly constrain the EOS., Uses REVTeX, 48 pages, 13 Postscript figures

We calculate neutrino cross sections from neutral current reactions in the dense matter encountered in the evolution of a newly born neutron star. Effects of composition and of strong interactions in the deleptonization and cooling phases of the evolution are studied. The influence of the possible presence of strangeness-rich hyperons on the neutrino scattering cross sections is explored. Due to the large vector couplings of the Sigma-minus and Cascade-minus, |C_V|~2, these particles, if present in protoneutron star matter, give significant contributions to neutrino scattering. In the deleptonization phase, the presence of strangeness leads to large neutrino energies, which results in large enhancements in the cross sections compared to those in matter with nucleons only. In the cooling phase, in which matter is nearly neutrino free, the response of the Sigma-minus hyperons to thermal neutrinos is the most significant. Neutrinos couple relatively weakly to the Lambda hyperons and, hence, their contributions are significant only at high density., Comment: 51 pages, 13 figures, ApJ in press

Neutrino processes in dense matter play a key role in the dynamics, deleptonization and the early cooling of hot protoneutron stars formed in the gravitational collapse of massive stars. Here we calculate neutrino mean free paths from neutrino-hyperon interactions in dense matter containing hyperons. Significant contributions to the neutrino opacity arise from scattering involving the Σ- hyperon, and absorption processes involving the neutral and Σ- hyperons. The estimates given here emphasize the need for (a) opacities which incorporate many-body effects in a multi-component mixture, and (b) new calculations of thermal and leptonic evolution of protoneutron stars with neutrino transport and equations of state with strangeness-rich matter.

We investigate the structure of neutron stars shortly after they are born, when the entropy per baryon is of order 1 or 2 and neutrinos are trapped on dynamical timescales. In all cases, the thermal effects for an entropy per baryon of order 2 or less are small when considering the maximum neutron star mass. Neutrino trapping, however, significantly changes the maximum mass due to the abundance of electrons. When matter is allowed to contain only nucleons and leptons, trapping decreases the maximum mass by an amount comparable to, but somewhat larger than, the increase due to finite entropy. When matter is allowed to contain strongly interacting negatively charged particles, in the form of strange baryons, a kaon condensate, or quarks, trapping instead results in an increase in the maximum mass of order $0.2M_\odot$, which adds to the effects of finite entropy. The presence of negatively-charged particles has two major implications. First, the value of the maximum mass will decrease during the early evolution of a neutron star as it loses trapped neutrinos, so that if a black hole forms, it either does so immediately after the bounce or it is delayed for a neutrino diffusion timescale of $\sim 10$ s. The latter case is most likely if the maximum mass of the hot star with trapped neutrinos is near $1.5M_\odot$. In the absence of negatively-charged hadrons, black hole formation would be due to accretion and therefore is likely to occur only immediately after bounce. Second, the appearance of hadronic negative charges results in a general softening of the equation of state that may be observable in the neutrino luminosities and average energies. Further, these additional negative charges decrease the electron fraction and may be observed in the relative excess of electron neutrinos compared to other neutrinos., Comment: 83 pages, 30 postscript figures, Physics Reports, to be published

We investigate the role of trapped neutrinos on the composition of protoneutron stars with quark-hadron phase transitions. Trapped neutrinos shift the transition to higher baryon densities and also reduce the extent of a mixed phase in comparison to neutrino-free matter. Thus, a mixed phase of baryons and quarks is more likely to occur after a neutrino diffusion time scale of several seconds. In contrast with stars containing only nucleons and leptons, stars with quarks have larger maximum masses when neutrinos are trapped than for neutrino-free stars. Hence, black hole formation is likely delayed for the neutrino diffusion time scale when quarks are present.

We examine the presence of strangeness-bearing components, hyperons and kaons, in dense neutron star matter. Calculations are performed using relativistic mean field models, in which both the baryon-baryon and kaon-baryon interactions are mediated by meson exchange. Results of kaon condensation are found to be qualitatively similar to previous work with chiral models, if compatibility of the kaon optical potentials is required. The presence of strangeness, be it in the form of hyperons or kaons, implies a reduction in the maximum mass and a relatively large number of protons, sufficient to allow rapid cooling to take place. The need to improve upon the poorly-known couplings of the strange particles, which determine the composition and structure of neutron stars, is stressed. We also discuss generic problems with effective masses in mean field theories., 36 pages, revtex, figures by fax/mail from authors

We consider the rate at which energy is emitted by neutrinos from the dense interior of neutron stars containing a Bose condensate of pions or kaons. The rates obtained are larger, by a factor of 2, than those found earlier, and are consistent with those found for the direct Urca processes., Comment: RevTeX, 10 pages

We have examined the contribution of the filled negative energy sea of hyperons to the energy/particle in nuclear matter at the one and two loop levels. While this has the potential to be significant, we find a strong cancellation between the one and two loop contributions for our chosen parameters so that hyperon effects can be justifiably neglected., Comment: 12 pages, latex, 1 simple figure attached at end (regular postscript)

We investigate the possibility of kaon condensation in the dense interior of neutron stars through the s--wave interaction of kaons with nucleons. We include nucleon--nucleon interactions by using simple parametrizations of realistic forces, and include electrons and muons in $\beta$--equilibrium. The conditions under which kaon condensed cores undergo a transition to quark matter containing strange quarks are also established. The critical density for kaon condensation lies in the range (2.3--5.0)$~\rho_0$, where $\rho_0=0.16$~fm$^{-3}$ is the equilibrium density of nuclear matter. For too large a value of the strangeness content of the proton, matter with a kaon condensate is not sufficiently stiff to support the lower limit of $1.44 M_\odot$ for a neutron star. Kaon condensation dramatically increases the proton abundance of matter and even allows positrons to exist inside the core. We also consider the case when neutrinos are trapped in the matter. Neutrino trapping shifts both kaon condensation and the quark matter transition to higher densities than in the case of cold, catalyzed matter. A newly--formed neutron star is expected to have a rather low central density, the density rising only after mass accretion onto the star ends after a few seconds. Thus, it is likely that if kaon condensation and/or the quark--hadron phase transition occur, they do so only during or after the mass accretion and neutrino trapping stages. We suggest that neutrino observations from a galactic supernova may provide direct evidence for or against a condensate and/or a quark--hadron transition., Comment: 31 Pages, 8 Tables ( LaTeX ), 14 uuencoded, tar-compressed postscript figures, NORDITA-93/29 N, SUNY-NTG-92-33

We have examined the properties of neutron-rich matter and finite nuclei in the modified relativistic Hartree approximation for several values of the renormalization scale, $\mu$, around the standard choice of $\mu$ equal to the nucleon mass $M$. Observed neutron star masses do not effectively constrain the value of $\mu$. However for finite nuclei the value $\mu/M=0.79$, suggested by nuclear matter data, provides a good account of the bulk properties with a sigma mass of about 600 MeV. This value of $\mu/M$ renders the effective three and four body scalar self-couplings to be zero at 60\% of equilibrium nuclear matter density, rather than in the vacuum. We have also found that the matter part of the exchange diagram has little impact on the bulk properties of neutron stars., Comment: 33 pages, Latex, 8 figures (available from authors by fax), Minnesota preprint NUC-MINN-93/7-T

We analyze the quark number susceptibility at high temperature in three-dimensional QCD where the susceptibility carries nonperturbative temperature effects at next-to-leading order. Using arguments of dimensional reduction, we show that the Coulomb bound state description used recently to describe the DeTar correlators is consistent with the free quark susceptibility, and offers a nonperturbative framework for discussing next-to-leading-order effects. The relevance of our results to four-dimensional QCD at high temperature is discussed.

We use optical and X-ray data to investigate the atmosphere of the isolated neutron star RX J185635-3754. The space motion suggests an origin about 2 million years ago in the Upper Cen-Lup OB association.

We investigate the generation of transverse momentum in high-energy heavy-ion collisions and its relation to the nuclear equation of state. We find that streamer chamber data can be fitted by Boltzmann-Uehling-Uhlenbeck calculations with a momentum-dependent potential that closely models realistic nuclear matter interactions and yields an equation of state with {ital K}=215 MeV.

Direct Urca processes with hyperons and/or nucleon isobars can occur in dense matter as long as the concentration of Lambda hyperons exceeds a critical value that is less than 3 percent and is typically about 0.1 percent. The neutrino luminosities from the hyperon Urca processes are about 5-100 times less than the typical luminosity from the nucleon direct Urca process, if the latter process is not forbidden, but they are larger than those expected from other sources. These direct Urca processes provide avenues for rapid cooling of neutron stars which invoke neither exotic states nor the large proton fraction (of order 0.11-0.15) required for the nucleon direct Urca process.

It has recently been claimed that a submillisecond pulsar has been observed in the remnant of SN 1987A. If the pulsations are due to rotation of a neutron star at this frequency, the equation of state (EOS) must be severely limited. In general, soft equations of state allow rapid enough rotational frequencies, but the softness is limited by the observed neutron star mass of 1.44 solar mass in the binary pulsar PSR 1913 + 16. In order to simultaneously satisfy these two constraints, that, in the vicinity of ordinary nuclear density, the pressure must vary relatively slowly with density, but at higher densities, the EOS must become relatively stiff and approach the causality limit. Specifically, in the absence of phase transitions above nuclear density and for cases in which the nuclear symmetry energy is an increasing function of density, the compression modulus of symmetric nuclear matter at the saturation density 0.16/cu fm must be less than about 160 MeV. If either of these situations occurs, higher values for the compression modulus may be possible, but, in any case, the EOS must still stiffen to the causal limit at high density. Examples of phase transitions that might permit rapid enough rotation are those due to pion or kaon condensates or to parity-doublet matter occurring around a few times the nuclear matter density.

We present results of microscopic calculations of the drift and diffusion coefficients in deep inelastic heavy ion collisions. Assuming the two nuclei to interact weakly, we make use of first-order perturbation theory (Golden Rule) for nucleon transfer and take into account the Pauli blocking effect. The nucleon transfer probability from one nucleus to the other is obtained using single particle wave functions. The results obtained are consistent with empirical estimates.

We extend the relativistic Brueckner-Hartree-Fock approach for nuclear matter to dense neutron matter. Special attention is devoted to contributions arising from tensor interactions due to the exchange of π-and ϱ-mesons and the dependence upon neutron-proton asymmetry. The role of the symmetry energy in studies of beta-stable neutron stars is also discussed.

An equation of state for cold nuclear matter for the region of densities ρnm−4ρnm, where ρnm is empirical nuclear-matter density, is constructed. We begin from the detailed calculation of Day and Wiringa for the two-body interactions; these give a saturation density of ∼2ρnm. This density is brought down to ρnm by the addition of relativistic corrections. Additional binding is obtained from three-body forces. A reasonable picture is obtained with the Day-Wiringa compression modulus for the two-body calculation, but the picture can be further improved by choosing this to be smaller. Our equation of state is similar to that of Friedman and Pandharipande in the region of nuclear matter denstiy ρnm, but, due to higher-order terms in the loop correction, is substantially softer at high density. Basically what happens is that the many-body effects saturate with increasing density, leaving only the two-body interactions. With this equation of state, prompt supernova explosions are very powerful when the compression modulus of neutron-rich matter (twice as many neutrons as protons) is ∼150 MeV, which corresponds to Knm ∼ 190 MeV for symmetric nuclear matter. Analysis shows that hot nuclear matter formed in heavy ion collisions demands a very stiff equation of state. We understand this as arising from the strong velocity dependence in the real part of the optical model potential which follows chiefly from the Lorentz character of the interactions, the vector mean field growing with increasing density and the scalar one decreasing. This gives a substantial repulsive contribution to the energy per particle and produces a stiff effective equation of state for several hundred MeV heavy-ion collisions. With increasing degree of equilibration the magnitude of the repulsive energy decreases since equilibration decreases the effective momentum. Given the strong velocity dependence in the interaction, the hot equation of state can be reconciled with the cool one.

The influence of momentum and frequency dependence of the nuclear mean field Σ on the level density parameter a is studied. By introducing a local quasiparticle effective mass we determine the volume, surface and curvature coefficients of a, expressed as a = a V A + a S A 2 3 + a c A 1 3 . It is found that the magnitude of ac is significant due to the very nature of the surface. A purely momentum dependent field Σ determined from the nonlocality of the optical potential gives a level density close to a self-consistent Thomas-Fermi description with Skyrme III forces. An explicit frequency dependence of Σ mainly influences as, enhancing it considerably for medium and heavy nuclei.

We derive analytic expressions for the Wigner transform (WT) of the one-body density matrix of a system of independent fermions in an N-dimensional harmonic oscillator (HO) potential. Considerable simplification is obtained for closed-shell configurations (all degenerate states occupied), when the Wigner transform (WT) depends only on the energy. Illustrative examples for one- and three-dimensional cases are discussed.

Using smoothed single-particle occupation numbers, the contribution of shell and surface effects to the static Wigner phase-space distribution function for non-interacting nucleons in an external, spherical, harmonic oscillator potential well is determined. The smoothing procedure illustrates clearly the strong quantum oscillations of the distributions function around the constant value for an infinite Fermi gas, and allows the separation of the contributions arising from shell effects connected with the structure of the single-particle level spectrum near the Fermi surface, and surface effects associated with single reflections of nucleons from the surface of the potential well. The temperature dependence of these effects in the distribution function is also investigated and a thermodynamical definition of the shell contribution to the kinetic energy density is suggested.

Photon production cross sections in intermediate energy heavy-ion reactions are calculated using detailed balance. The model gives substantial photon yields and reproduces qualitatively the experimental observations. A possible influence of the ..delta..-isobar degree of freedom on the high energy photon yield is pointed out.

A simple model which includes the effects of primary degradation is shown to be able to reproduce FERMILAB data for transverse energy production in pA collisions of 800 GeV protons on all targets from protons to 208 Pb.

Prompt emission of nucleons is observed in time-dependent Hartree-Fock calculations of $^{16}\mathrm{O}$+$^{93}\mathrm{Nb}$ collisions. These nucleons are emitted in the forward direction in about 2\ifmmode\times\else\texttimes\fi{}10$^{\ensuremath{-}22}\mathrm{s}$ after the contact of the ions, with a mean velocity somewhat less than the beam velocity. At $E(\mathrm{lab})=204$ MeV, the estimated total nucleon cross section is \ensuremath{\sim}230 mb. For central collisions a lower energy threshold of 130 MeV is established. Force dependence of the results is studied in detail.

We examine the application of transition-state theory for fission-fragment angular distributions to composite nuclei near the limits of stability. The possible roles of saddle-point and scission-point configurations are explored. For many heavy-ion reactions that involve large angular momenta, the observed anisotropies are between the predictions of the saddle-point and scisson--point models. Empirical correlations are shown between the effective moments of inertia and the spin and Z 2 A of the compound nucleus. These correlations provide evidence for a class of transition-state nuclei intermediate between saddle- and scission-point configurations. An important indication of these patterns is that the speed of collective deformation toward fission may well be slow enough to allow for statistical equilibrium in the tilting mode even for configurations well beyond the saddle point.

The nucleon exchange process in deep-inelastic collisions is investigated by studying the one-way current constructed using the Wigner transform of the time-dependent Hartree-Fock one-body density matrix. Detailed calculations for head-on $^{16}\mathrm{O}$+$^{16}\mathrm{O}$ collisions at three different bombarding energies have been performed. A combination of two simple models for the contributions from relative motion and tunneling is shown to predict one-way currents close to the time-dependent Hartree-Fock results.

Charmonium bound states immersed in a coherent chromo-electric field are easily ripped apart for field strengths comparable to the QCD string tension. Estimates based on flux tube models suggest that field strengths of such magnitude may be achieved in heavy-ion collisions at ultrarelativistic energies. Our results suggest that charmonium suppression would not discriminate between a coherent and a thermalized post collision state in relativistic heavy-ion collisions.

We study the flow of matter, momentum and energy in low energy heavy-ion collisions. This is done by using the Wigner phase space distribution function to calculate quantum mechanical analogs of the classical distributions of the observables. We apply the Wigner transformation to time dependent Hartree-Fock calculations of 16O + 16O and 40Ca + 40Ca reactions. Both static and dynamic features of the distribution functions are demonstrated.

The relationship between the maximum neutron-star mass and observable parameters of the equation of state is explored. In particular, the roles of the nuclear incompressibility and the symmetry energy are considered. It is concluded that, for realistic symmetry energies, the compression modulus cannot, by itself, be severely limited by observed neutron-star masses. Several directions for further study are suggested.

A number of difficult problems are encountered in attempts to incorporate the strange quark into hadronic structure by generalizing from two to three flavors because the mass of the strange quark m s ≈ 175 MeV ≈ Λ QCD . This mass is neither small nor large. A question of particular interest is as to the ss content of the nucleon. If it is large, it is likely that strangeness condensation will occur at densities ϱ ≈ 3 ϱ o , where ρ o is nuclear matter density. In order to gain insight into the mechanism for strangeness condensation, s-wave neutral pion condensation is first investigated. Then the analogous problem of strangeness condensation, once the SU(3) × SU(3) problem is reduced to an SU(2) × SU(2) one by using V spin, can be simply investigated. The role of the strange quark mass in quark condensates is investigated, employing the Nambu-Jona-Lasinio formalism. In the large N c limit, the quark flavors decouple, but in order 1/N c are strongly mixed by the determinantal interaction between quarks which arises once instantons are integrated out. This suggests a possible mechanism for the strange quark mass to affect the nucleon energy and for the ss content of the nucleon to be large.

The asymmetry dependence of the incompressibility at fixed density, the density at fixed pressure, and the isobaric incompressibility are studied for neutron-rich nuclear matter at arbitrary densities. Simple expressions valid to all orders in density and to second order in asymmetry are derived involving the density derivatives of the Landau parameters of the symmetric system. Illustrative calculations are performed with different equations of state.

Nuclear matter overlap integrals between two nuclei are calculated for density distributions generated by folding a short range function over arbitrarily shaped sharp surfaces of the two nuclei. Explicit formulas are derived for two choices of the folding function, viz., a Gaussian and a Yukawa function. An approximation scheme is given to facilitate a quick evaluation of the overlap integrals and is found to give results which are in good agreement with the exact results over a wide range of masses and spheroidal deformations of the two nuclei.

By calculating the inclusive cross sections for Δ -hole and nucleon -hole excitations in peripheral nucleus-nucleus collisions, pion production cross sections are estimated. An intermediate energies, this collective mechanism may be verified by coincidence measurements.

Charmonium bound states immersed in a coherent chromo-electric field are easily ripped apart for field strengths comparable to the QCD string tension. Estimates based on flux tube models suggest that field strengths of such magnitude may be achieved in heavy-ion collisions at ultrarelativistic energies. Our results suggest, that charmonium suppression would not discriminate between a coherent and a thermalized post collision state in rela.tivistic heavy-ion collisions.

A unified approach is used to describe quasielastic and fusion processes in heavy-ion reactions at near barrier energies. The spin distributions for fusion are used in conjunction with transition-state theory to calculate fission fragment angular distributions. Results for the reaction /sup 16/O+/sup 208/Pb show that when transfer contributions are small, satisfactory agreement with data is obtained. The role of fragment anisotropy as a useful probe of entrance channel effects at energies close to the barrier is pointed out.

The stress-energy tensor and entropy are calculated for non-interacting quarks and gluons confined to a slab of thickness L at finite temperature T . Slab propagators for quarks and gluons are constructed. For T = 200 MeV corrections to the Stefan-Boltzmann results are less than 10% if L ⩾ 1.5 fm. If L is less than this, corrections become substantial, for example, pressures exhibit marked directional asymmetries. Implications for the calculation of the evolution of quark-gluon plasmas expected in heavy-ion collisions are discussed.

It is shown that no definite conclusions can be drawn regarding the magnitude of energy dissipation in fission during the descent from the saddle point, by a comparison of the calculated deformation and interaction energies of fission fragments near scission, with the experimental fragment excitation and kinetic energies. This is contrary to the conclusions drawn by Schultheis and Schultheis on the basis of a similar analysis. The reasons for this discrepancy are also discussed.

It is found that for level schemes obtained from a folded Yukawa potential, the Strutinsky smearing procedure for the evaluation of the shell correction to the total potential energy of nuclei does not lead to a unique value for nuclear shapes near and beyond the outer fission barrier deformations and consequently introduces uncertainties in the relative fission barrier heights.

We use the extended Thomas-Fermi approximation and Skyrme-type interactions to describe the energy density of a semi-infinite slab of neutron-rich nuclear matter at zero temperature. We allow for the existence of a drip phase at low proton fractions in addition to the more dense nuclear phase. We determine various bulk properties of both phases when the system is in equilibrium. We extend the usual definition of the surface energy to apply to the case where drip is present. Assuming the density profile has the form of a Fermi function to a power, we perform a constrained variational calculation to determine the parameters of the density profile. The surface and curvature energies are calculated for proton fractions ranging from 0.5 (symmetric nuclear matter) to 0 (pure neutron matter) for typical Skyrme-type interactions. We find significantly different asymmetry dependences for different interactions. For proton fractions close to 0.5, our results are in close agreement with the predictions of the droplet model. We also present results of calculations for fission barrier properties and phase transitions between nuclei and bubbles to highlight the role of surface and curvature energies in the neutron-rich regime.

Pion production in heavy ion collisions at energies below the free nucleon-nucleon threshold, i.e., at energies, where the pion mass exceeds the kinetic energy of a projectile nucleon in the zero momentum frame, has been discussed for a long time in terms of probing the intrinsic Fermi motion in the projectile and target nuclei. However, as the beam energy is lowered, this process gets more and more unlikely and below a certain energy it should not be observed anymore. In a sharp cut-off Fermi gas model this occurs at E/sub lab/=50 MeV/u. However, as long as the total center of mass energy exceeds the pion mass, pions still can be produced by a cooperative sharing of the beam energy of several (or all) projectile nucleons. The experiments presented here are meant to extend the experimental information into that kinematic domain and represent the up to now lowest beam energy, where pion production has been identified unambiguously. The production of a pion of 100 MeV kinematic energy with a 35 MeV/u /sup 14/N beam requires Fermi momenta as high as approx.350 MeV/c or alternatively 60% of the total beam energy. The information from the present experiments together with the results ofmore » previous experiments at higher beam energies of 44 MeV/u and 60 to 84 MeV/u allows one to distinguish between the alternative production mechanisms.« less

For near central collisions of Nb on Nb at a laboratory energy of 650 MeV per projectile nucleon we calculate inclusive cross sections as a function of the azimuthal angle where this angle is measured from the reaction plane. The azimuthal dependence is strongly influenced by the nuclear equation of state and is a useful quantity to measure.

We examine the role of many-body effects provided by the chiral sigma model in the equation of state of symmetric nuclear matter and neutron-rich matter. Using the parameters determined by fitting the known equilibrium properties of symmetric and slightly neutron-rich matter, the equation of state with arbitrary neutron excess is calculated. The role of the nuclear symmetry energy on the structure of beta stable neutron stars is discussed.

We perform the first study of the principal core $g$-mode oscillation in hybrid stars containing quark matter, utilizing a crossover model for the hadron-to-quark transition inspired by lattice QCD. The ensuing results are compared with our recent findings of $g$-mode frequencies in hybrid stars with a first-order phase transition using Gibbs constructions. We find that models using Gibbs construction yield $g$-mode amplitudes and the associated gravitational energy radiated that dominate over those of the chosen crossover model owing to the distinct behaviors of the equilibrium and adiabatic sound speeds in the various models. Based on our results, we conclude that were $g$-modes to be detected in upgraded LIGO and Virgo detectors it would indicate a first-order phase transition akin to a Gibbs construction., 15 pages, 11 figures, 3 tables; refs. and discussion added, accepted for publication in PRD

We study the equation of state (EOS) of kaon-condensed matter including the effects of temperature and trapped neutrinos. It is found that the order of the phase transition to a kaon-condensed phase, and whether or not Gibbs' rules for phase equilibrium can be satisfied in the case of a first order transition, depend sensitively on the choice of the kaon-nucleon interaction. The main effect of finite temperature, for any value of the lepton fraction, is to mute the effects of a first order transition, so that the thermodynamics becomes similar to that of a second order transition. Above a critical temperature, found to be at least 30--60 MeV depending upon the interaction, the first order transition disappears. The phase boundaries in baryon density versus lepton number and baryon density versus temperature planes are delineated. We find that the thermal effects on the maximum gravitational mass of neutron stars are as important as the effects of trapped neutrinos, in contrast to previously studied cases in which the matter contained only nucleons or in which hyperons and/or quark matter were considered. Kaon-condensed EOSs permit the existence of metastable neutron stars, because the maximum mass of an initially hot, lepton-rich protoneutron star is greater than that of a cold, deleptonized neutron star. The large thermal effects imply that a metastable protoneutron star's collapse to a black hole could occur much later than in previously studied cases that allow metastable configurations., 24 pages, 17 figures

We study the effects of very strong magnetic fields on the equation of state (EOS) in multicomponent, interacting matter by developing a covariant description for the inclusion of the anomalous magnetic moments of nucleons. For the description of neutron star matter, we employ a field-theoretical approach which permits the study of several models which differ in their behavior at high density. Effects of Landau quantization in ultra-strong magnetic fields ($B>10^{14}$ Gauss) lead to a reduction in the electron chemical potential and a substantial increase in the proton fraction. We find the generic result for $B>10^{18}$ Gauss that the softening of the EOS caused by Landau quantization is overwhelmed by stiffening due to the incorporation of the anomalous magnetic moments of the nucleons. In addition, the neutrons become completely spin polarized. The inclusion of ultra-strong magnetic fields leads to a dramatic increase in the proton fraction, with consequences for the direct Urca process and neutron star cooling. The magnetization of the matter never appears to become very large, as the value of $|H/B|$ never deviates from unity by more than a few percent. Our findings have implications for the structure of neutron stars in the presence of large frozen-in magnetic fields., 40 pages, 7 figures, accepted for publication in ApJ