Gravity seminar - Cristina Manuel Seminar

We study the phonon contribution to different transport coefficients in the core of superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes. These techniques are rather general and allow us to write the phonon collisional frequencies as a function of the equation of state (EoS) of the system. At sufficiently low temperature T the phonons become ballistic. We analyze the shear viscosity taking into account the contribution of superfluid phonons to the viscosity, both in their hydrodynamical and ballistic regime. We compare to recent calculations of the shear viscosity from electron collisions and comment on the possible consequences for r-mode damping in superfluid neutron stars.  Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars, except for n ~ 2n0 when the opening of the URCA processes takes place.