Photon Emission from Dense Quark Matter

Thermal emission rates and mean free paths of photons in a color-flavor locked (CFL) phase of quark matter at high densities and moderate temperatures are evaluated. Our calculations are based on a low-energy effective theory for CFL matter describing Goldstone boson excitations and their electromagnetic as well as strong interactions. Inmedium coupling strengths of vector mesons are found to be smaller than in vacuum. As a consequence of in-medium modified pion dispersion relations, novel processes such as π+π− → γ and γ → π+π− become possible. The total photon emissivity is found to be very large, exceeding contributions from thermal e+e− annihilation above temperatures of about 5 MeV. At the same time, the corresponding mean free paths become very small. Our results imply that the photon flux from the surface of a (hypothetical) CFL star in its early hot stages saturates the black-body limit. Estimates for the early thermal evolution of the star are also presented.