Neutrino transport in young neutron stars

In Part one of this thesis, the transport coefficients of degenerate neutrinos in dense matter are calculated taking into account both absorption and scattering of neutrinos by nucleons. Exact solutions of the transport equation are used, and the effect of neutron-proton interactions on the composition of the matter is allowed for. Energy dissipation by neutrinos is considered and it is shown that under many circumstances diffusion of neutrinos is more important than neutrino viscosity or heat conduction. In Part two, the results of Part one are used to numerically solve the nonlinear diffusion equation which describes the loss of neutrinos from the inner core of a newly formed neutron star. It is found that the time for the neutrinos to escape cannot be less than about one second. This time is primarily determined by the transport processes in the core and is insensitive to the boundary condition. Energy dissipation is calculated due to neutrino loss and find that the total amount of dissipation is rather insensitive to the diffusion coefficient. Maximum dissipation occurs in the outer regions of the core where the diffusion coefficient is the largest and the heat capacity is the lowest. The temperature increase is modest and so not sufficient to significantly increase the pressure. It is concluded that the loss times are too long for neutrino escape to be dynamically useful in matter ejection processes which occur on millisecond time scales. The loss of these neutrinos can therefore be neglected in determining the dynamical processes of neutron star formation and supernovae