Neutrino emission and pion condensation in dense matter
PART I We formulate the description of neutrino pair emission in dense matter in terms of the correlation functions of the background matter, and consider in detail, at densities and temperatures expected for neutron stars, the neutrino··pair bremsstrahlung emission from electrons in a static lattice and the one phonon corrections to this process. The one phonon corrections are important for temperatures greater than the Debye temperature of the lattice and become as large as the static lattice contributions near the melting temperature of the lattice. However, when the one phonon contributions are of most importance the plasma neutrino process is usually the dominant energy loss mechanism. The decay of mu1tiphonon states into neutrinos is also considered and we find this process to be negligible for acoustic phonons due to phase space restrictions. At high densities (p ~1014g/cc) we consider the role played by electrons scattering from degenerate neutrons and protons in the emission of neutrinos. These processes can be important if either the neutrons or the protons (but not both) are superf1uid. PART II The equilibrium thermodynamic conditions obeyed by a pion condensed state of dense neutron or neutron star matter are derived. Then simple model calculations of negative pion condensation that satisfy the equilibrium conditions are carried out. In the simplest of these models (p-wave pion-nucleon interaction a1one) it is found that matter is unstable to the formation of a condensed pion mode. This model is made more realistic by including other forces: s-wave pion-nucleon interactions pi-pi interactions, and phenomenological form factors in these interactions. These modifications have little influence on the stability of the system. Finally, effects of repulsive nuclear forces on pion condensation are considered in a simple model, in which we retain only a simplified repulsive zero range nucleon-nucleon interaction proportional to a.a' T·T' The density for the pion threshold is very sensitive to the strength of this force. This model of the nuclear force greatly reduces the instability of the system, although it is too crude to restore stability completely. It also indicates the important role nuclear forces play in a correct description of the pion condensed phase.
Neutrinos, neutrino pair emission, Bremsstrahlung, negative pion condensation, pion decay
University of Illinois - Urbana-Champaign
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