Neutrino-nucleon scattering in supernova matter from the virial expansion

Understand

We generalize our virial approach to study the neutral current neutrino response of nuclear matter at low densities.

• In the long-wavelength limit, the virial expansion makes model-independent predictions for neutrino-nucleon scattering rates and the density S_V and spin S_A responses.
• We find S_A is significantly reduced from one even at low densities.
• We provide a simple fit S_A^f(n,T,Y_p) of the axial response as a function of density n, temperature T and proton fraction Y_p.