On the Cooling of the Neutron Star in Cassiopeia A

We demonstrate that the high-quality cooling data observed for the young neutron star in the supernova remnant Cassiopeia A over the past 10 years--as well as all other reliably known temperature data of neutron stars--can be comfortably explained within the "nuclear medium cooling" scenario. The cooling rates of this scenario account for medium-modified one-pion exchange in dense matter and polarization effects in the pair-breaking formations of superfluid neutrons and protons. Crucial for the successful description of the observed data is a substantial reduction of the thermal conductivity, resulting from a suppression of both the electron and nucleon contributions to it by medium effects. We also find that possibly in as little as about ten years of continued observation, the data may tell whether or not fast cooling processes are active in this neutron star.Comment: 4 pages, 3 figure

Strangeness Balance in HADES Experiments and the Xi- Enhancement

HADES data on a strangeness production in Ar+KCl collisions at 1.76A GeV are analyzed within a minimal statistical model. The total negative strangeness content is fixed by the observed K^+ multiplicities on event-by-event basis. Particles with negative strangeness are assumed to remain in chemical equilibrium with themselves and in thermal equilibrium with the environment until a common freeze-out. Exact strangeness conservation in each collision event is explicitly preserved. This implies that Xi baryons can be released only in events where two or more kaons are produced. An increase of the fireball volume due to application of a centrality trigger in HADES experiments is taken into account. We find that experimental ratios of K-/K+, Lambda/K+ and Sigma/K+ can be satisfactorily described provided in-medium potentials are taken into account. However, the calculated Xi-/Lambda/K+ ratio proves to be significantly smaller compared to the measured value (8 times lower than the experimental median value and 3 times lower than the lower error bar). Various scenarios to explain observed Xi enhancement are discussed. Arguments are given in favor of the Xi production in direct reactions. The rates of the possible production processes are estimated and compared.Comment: 13 pages, 3 figure

Diquark Condensates and Compact Star Cooling

The effect of color superconductivity on the cooling of quark stars and neutron stars with large quark cores is investigated. Various known and new quark-neutrino processes are studied. As a result, stars being in the color flavor locked (CFL) color superconducting phase cool down extremely fast. Quark stars with no crust cool down too rapidly in disagreement with X-ray data. The cooling of stars being in the N_f =2 color superconducting (2SC) phase with a crust is compatible with existing X-ray data. Also the cooling history of stars with hypothetic pion condensate nuclei and a crust does not contradict the data.Comment: 10 pages, 5 figures, accepted for publication in Ap