Probing Quark Matter In Neutron Stars

The presence of quark matter in neutron star interiors may have distinctive signatures in basic observables such as (i) masses and radii [1], (ii) surface temperatures versus age [2], (iii) spin-down rates of milli-second pulsars [3], and (iv) neutrino luminosities from future galactic core collapse supernovae [4]. I highlight recent developments in some of these areas with a view towards assessing how theory may be confirmed by $\nu-$signals from future galactic supernovae in detectors like SuperK, SNO and others under consideration, including UNO [5], and by multi-wavelength photon observations with new generation satellites such as the HST, Chandra, and XMM.Comment: 4 pages, 2 figures. To appear in the proceedings of QM 2001. Uses fleqn.sty and espcrc1.st

Bulk Viscosity of Interacting Hadrons

We show that first approximations to the bulk viscosity $\eta_v$ are expressible in terms of factors that depend on the sound speed $v_s$, the enthalpy, and the interaction (elastic and inelastic) cross section. The explicit dependence of $\eta_v$ on the factor $(\frac 13 - v_s^2)$ is demonstrated in the Chapman-Enskog approximation as well as the variational and relaxation time approaches. The interesting feature of bulk viscosity is that the dominant contributions at a given temperature arise from particles which are neither extremely nonrelativistic nor extremely relativistic. Numerical results for a model binary mixture are reported.Comment: 4 pages, 1 figure, Contribution to Quark Matter 2009, Knoxville, Tennessee, US