Bulk viscosity coefficients due to phonons in superfluid neutron stars

Understand

We calculate the three bulk viscosity coefficients as arising from the collisions among phonons in superfluid neutron stars.

• We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state of the system.
• The solution of the dynamical evolution of the phonon number density allows us to calculate the bulk viscosity coefficients as function of the phonon collisional rate and the phonon dispersion law, which depends on the neutron pairing gap.
• Our method of computation is rather general, and could be used for different superfluid systems, provided they share the same underlying symmetries.