Tests of Low-Scale Leptogenesis in Charged Lepton Flavour Violation Experiments

TL;DR

This paper explores how low-energy charged lepton flavor violation experiments can test low-scale leptogenesis models involving quasi-degenerate heavy Majorana neutrinos with masses from 0.05 to 500,000 GeV.

Contribution

It derives constraints on leptogenesis parameters from existing experiments and shows future experiments can probe significant parts of the parameter space.

Findings

Current experiments limit heavy neutrino couplings and masses.

Upcoming experiments can potentially discover signals of low-scale leptogenesis.

Certain tau decay experiments can also probe parts of the parameter space.

Abstract

We consider low-energy tests of low-scale leptogenesis based on the type I seesaw scenario with three right-handed singlet neutrinos $\nu_{l R}$. In this scenario, successful leptogenesis is possible for quasi-degenerate in mass heavy Majorana neutrinos $N_{1,2,3}$, $M_{1,2,3}\cong M$, $|M_j - M_i|\ll M$, $i\neq j = 1,2,3$, heavy Majorana neutrino masses $M \sim (0.05 - 5\times 10^5)$ GeV, and $N_j$ charged current and neutral current weak interaction couplings as large as $\mathcal{O}(10^{-2})$. We derive the constraints on the corresponding leptogenesis parameter space from the existing data from low-energy experiments, including the limits from the experiments on $\mu \rightarrow e \gamma$ decay and on the rate of $\mu - e$ conversion in gold. We show also that the planned and upcoming experiments on charged lepton flavour violation with $\mu^\pm$, MEG II on the $\mu \rightarrow e\gamma$ decay, Mu3e on $\mu \rightarrow eee$ decay, Mu2e and COMET on $\mu - e$ conversion in aluminium and PRISM/PRIME on $\mu - e$ conversion in titanium, can probe significant region of the viable leptogenesis parameter space, and thus have a potential for a discovery. Experiments on $\tau \to eee(\mu\mu\mu)$ and $\tau \to e(\mu)\gamma$ decays (e.g., BELLE II) also can probe a part of the leptogenesis parameter space, although a relatively small one.