2025/01/13 by Mojahed, Martin A., Schmitz, Kai, Wilken, Dominik · 1 citation
#FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc) #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2501.07634
Leptogenesis is an attractive scenario for the generation of the baryon asymmetry of the Universe that relies on the dynamics of right-handed neutrinos (RHNs) in the seesaw extension of the Standard Model. In standard thermal leptogenesis, the RHN mass scale MN is subject to the Davidson--Ibarra bound, MN \gtrsim 109 \textrmGeV, which builds on the assumption that RHN decays are responsible for the violation of both charge-parity invariance (CP) and baryon-minus-lepton number (B - L). In this paper, we relax this assumption in the context of the more flexible framework of wash-in leptogenesis, in which CP violation is encoded in the initial conditions and the only remaining task of the RHN decays is to violate B - L. Solving the relevant set of Boltzmann equations for vanishing initial baryon and lepton numbers (i.e., B = Le = Lμ= Lτ= 0 initially), we find that, in wash-in leptogenesis, the RHN mass scale can be as low as 7~TeV. Wash-in leptogenesis at such low RHN masses requires the presence of a primordial charge asymmetry between right-handed electrons and left-handed positrons. We discuss several possibilities for the origin of such an asymmetry and comment on its implications for the chiral instability of the Standard Model plasma.