Multiple-scattering suppression of the bremsstrahlung emission of neutrinos and axions in supernovae

In a supernova core the nucleon collision rate ${\mathrm{\Gamma }}_{\mathrm{coll}}$ far exceeds oscillation frequency of neutrino or axion radiation originating from nucleon bremsstrahlung processes of the type NN→NN+νν¯ or a. Therefore, including the imaginary part of the self-energy in the effective nucleon propagator, the rate for such processes is suppressed by a factor [1+(${\mathrm{\Gamma }}_{\mathrm{coll}}$/ξT${)}^2$ ${]}^{\mathrm{-}1}$, where ξ is a numerical factor and T is the temperature. Previous SN 1987A bounds on axions, right-handed neutrinos, and other particles must be relaxed accordingly.