Narrow Results

In the present paper, we study exotic phases in hot neutron–proton–electron (NPE) matter. It is shown that for densities lower than the normal nuclear matter inhomogeneous (exotic or pasta) phases may be present. This is believed to occur due to the so-called frustration mechanism, i.e., a close competition between the surface and Coulomb energy which, in certain cases, favors exotic phases instead of homogeneous matter. These structures may have important effects in the cooling of neutron stars, for example, affecting the neutrino opacity.

The diffusion coefficients that are related to the neutrino opacities are calculated in such a way that the formation of nuclear pasta and homogeneous matter at low densities are taken into account. Two methods are developed to build the pasta phase and their differences are outlined. One of them is chosen as part of a complete equation of state used in the calculation of the diffusion coefficients. Our results show that the mean free paths are significantly altered by the presence of nuclear pasta in stellar matter when compared with the results obtained with pure homogeneous matter. These differences in neutrino opacities will have consequences in the calculation of the Kelvin-Helmholtz phase of protoneutron stars.