Effects of non-standard neutrino-electron interactions in relic neutrino decoupling

Abstract

We consider the decoupling of neutrinos in the early Universe in presence of non‐standard neutral current neutrino‐electron interactions (NSI). We present the results of fully numerical and momentum‐dependent calculations, including flavor neutrino oscillations. We find that the presence of neutrino‐electron NSI may enhance the entropy transfer from electron‐positron pairs into neutrinos instead of photons, up to a value of the effective number of neutrinos Neff≃3.12 for NSI parameters within the ranges allowed by present laboratory data, which is almost three times the effect that appears for standard weak interactions. Thus non‐standard neutrino‐electron interactions do not essentially modify the density of relic neutrinos nor the bounds on neutrino properties from cosmological observables, such as their mass.