Speaker
Description
The cosmic neutrino background, for which there is ample indirect evidence, is a remnant from when the universe was just one second old. I will discuss the rate at which neutrinos interact with a QED plasma, around MeV temperatures (just prior to their decoupling). Computing the NLO interaction rate as a function of the neutrino momentum and flavour, we recently found relative corrections on the few percent level [1]. One of the main ingredients is the electron-positron spectral function, of which both physical polarization states are needed (transverse and longitudinal with respect to spatial momentum). In addition to the spectral function, the interaction rate also depends on an effective neutrino-antineutrino-photon vertex. The latter gives rise to scatterings with Bose-enhanced $t$-channel photons and hence necessitates the resummation of hard-thermal-loops.
[1] G. Jackson, M. Laine, JHEP 05 (2024), 089 [arXiv:2312.07015]
