Neutrino dynamics below the electroweak crossover

Understand

We estimate the thermal masses and damping rates of active (m < eV) and sterile (M ~ GeV) neutrinos with thermal momenta k ~ 3T at temperatures below the electroweak crossover (5 GeV < T < 160 GeV).

• These quantities fix the equilibration or &#34;washout&#34; rates of Standard Model lepton number densities.
• Sterile neutrinos interact via direct scatterings mediated by Yukawa couplings, and via their overlap with active neutrinos.
• Including all leading-order reactions we find that the washout rate generally exceeds the Hubble rate for 5 GeV < T < 30 GeV.