Beta equilibrium and bulk viscosity in neutron star mergers

Neutron star mergers are laboratories of hot and dense nuclear matter, including
its response to temperature and density changes that
occur on millisecond timescales. This gives them the ability to probe
dynamical properties that may help us to uncover exotic phases.
Beta (proton fraction) equilibration, which can occur on the same timescale,
plays a crucial role in the physics of mergers.
I will talk about corrections to the traditional criteria for beta
equilibrium that become significant in neutron star mergers, and
the likely role of bulk viscosity arising from the processes
that establish beta equilibrium.