2022/09/01 by M. Yoshimura, Yoshimura, M.
Physics and Astronomy · #Particle physics theoretical and experimental studies #Neutrino Physics Research #Dark Matter and Cosmic Phenomena
paper · pdf · doi:10.48550/arxiv.2209.00166
It is known that the Schwinger mechanism of vector-like QED theory is afflicted by a logarithmic singularity under background electromagnetic field due to a hypothetical massless charged fermion. We extend singularity analysis to a more realistic case of the chiral electroweak theory, to show that the effective lagrangian under background gauge field at zero temperature exhibits a similar instability proportional to ln (1/mν2) with mν a small neutrino mass. Moreover, the effective lagrangian of chiral fermion loop contains CP violating pieces proportional to background gauge fields in odd powers of EZ⋅BZ or (EW+⋅BW-+ EW-⋅BW+)/2 . This brings in a new source of CP violation and time-reversal symmetry violation in the standard particle theory independent of the Kobayashi-Maskawa phase of quark mass mixing matrix. The effective action in thermal equilibrium at finite temperature T is then calculated under background SU(2)× U(1) gauge fields in the spontaneously broken phase. An even more singular power-law behavior ∝ (mν T)-5/2 is found and it contains CP violating term as well. The case of Majorana neutrino satisfies almost all necessary conditions to generate a large lepton number asymmetry, though not necessarily convertible to a baryon asymmetry due to lower cosmic temperatures at which this may occur.