Two-neutrino five-photon scattering at low energies

We extend earlier constructions of the effective action for neutrino-photon scattering, using the connection between low-energy neutrino-photon and photon-photon scattering together with the known effective Lagrangian describing low-energy photon scattering in QED. We use this effective action to calculate analytic expressions for the low-energy cross section for the (unpolarized) processes νν¯→5γ, νγ→ν+4γ, and γγ→νν¯+3γ. As a byproduct we derive compact expressions for the N-body phase-space integrals for massless particles, including those having nontrivial tensor structure.