Search

Baryon and quark superfluidity in the cooling of neutron stars are investigated. Observations could constrain combinations of the neutron or Lambda-hyperon pairing gaps and the star's mass. However, in a hybrid star with a mixed phase of hadrons and quarks, quark gaps larger than a few tenths of an MeV render quark matter virtually invisible for cooling. If the quark gap is smaller, quark superfluidity could be important, but its effects will be nearly impossible to distinguish from those of other baryonic constituents., Comment: 4 pages, 3 ps figures, uses RevTex(aps,prl). Submitted to Phys. Rev. Lett

We study various non-equilibrium properties of a mixture comprised of pions, kaons and nucleons. The concentration of the constituents is chosen to mimic those expected in the mid-rapidity interval of CERN and RHIC experiments. The heavier kaons and nucleons are found to equilibrate more slowly than pions. These results shed new light on the influence of collective flow effects on the transverse momentum distributions of kaons and nucleons versus those of pions in ultrarelativistic nuclear collisions.

The QCD sum-rule approach for a nuclear medium is developed. The medium dependence of the neutron-proton mass difference calculated from this approach gives effects in nuclei which have direct relevance for the resolution of the Okamoto-Nolen-Schiffer anomaly.

We show that the direct URCA process can occur in neutron stars if the proton concentration exceeds some critical value in the range 11--15%. The proton concentration, which is determined by the poorly known symmetry energy of matter above nuclear density, exceeds the critical value in many current calculations. If it occurs, the direct URCA process enhances neutrino emission and neutron star cooling rates by a large factor compared to any process considered previously.

We demonstrate that the largest measured mass of a neutron star establishes an upper bound to the energy density of observable cold baryonic matter. An equation of state-independent expression satisfied by both normal neutron stars and self-bound quark matter stars is derived for the largest energy density of matter inside stars as a function of their masses. The largest observed mass sets the lowest upper limit to the density. Implications from existing and future neutron star mass measurements are discussed.

Neutrino fluxes from proto-neutron stars with and without quarks are studied. Observable differences become apparent after 10--20 s of evolution. Sufficiently massive stars containing negatively-charged, strongly interacting, particles collapse to black holes during the first minute of evolution. Since the neutrino flux vanishes when a black hole forms, this is the most obvious signal that quarks (or other types of strange matter) have appeared. The metastability timescales for stars with quarks are intermediate between those containing hyperons and kaon condensates., 4 pages including 4 figures. Version with minor revisions. To be published in Physical Review Letters

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.

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.

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 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.