Large amplitude behavior of the bulk viscosity of dense matter

Understand

We study the bulk viscosity of dense matter, taking into account non-linear effects which arise in the large amplitude "supra-thermal" region where the deviation $\mu_\Delta$ of the chemical potentials from chemical equilibrium fulfills $\mu_\Delta>T$.

• This regime is relevant to unstable modes such as r-modes, which grow in amplitude until saturated by non-linear effects.
• We study the damping due to direct and modified Urca processes in hadronic matter, and due to nonleptonic weak interactions in strange quark matter.
• We give general results valid for an arbitrary equation of state of dense matter and find that the viscosity can be strongly enhanced by supra-thermal effects.