Neutrino breakup of A=3 nuclei in supernovae

We extend the virial equation of state to include H3 and He3 nuclei, and predict significant mass-three fractions near the neutrinosphere in supernovae. While alpha particles are often more abundant, we demonstrate that energy transfer cross sections for muon and tau neutrinos at low densities are dominated by breakup of the loosely-bound H3 and He3 nuclei. The virial coefficients involving A=3 nuclei are calculated directly from the corresponding nucleon-H3 and nucleon-He3 scattering phase shifts. For the neutral-current inelastic cross sections and the energy transfer cross sections, we perform ab initio calculations based on microscopic two- and three-nucleon interactions and meson-exchange currents.