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

In a supernova core the nucleon collision rate Γcoll far exceeds oscillation frequency of neutrino or axion radiation originating from nucleon bremsstrahlung processes of the type NN→NN+ν bar ν 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+(Γcoll/ξT)2]-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