Which neutrino interactions actually matter in colliding neutron stars?

When two neutron stars collide, neutrinos streaming from the hot merger remnant shape the chemical composition and light emission. Using detailed Monte Carlo simulations, researchers tracked how different neutrino interaction channels—absorption, scattering, pair production—vary across extreme density and temperature regions. They found that pair annihilation in cold, low-density zones and previously ignored inelastic electron scattering significantly affect heavy-lepton neutrinos, implying current merger models underestimate these cooling and thermalization processes.