Leptogenesis Constraints on the Mass of Right-handed Gauge Bosons

TL;DR

This paper explores how leptogenesis constraints on the right-handed $W$-boson mass in a TeV-scale Left-Right symmetric model can be relaxed under certain conditions, allowing for potentially discoverable $W_R$ masses at the LHC.

Contribution

It demonstrates that in specific models with larger Yukawa couplings, the lower bound on $W_R$ mass from leptogenesis can be reduced to about 3 TeV, making detection feasible.

Findings

Leptogenesis bound on $W_R$ mass can be as low as 3 TeV.

Models with larger Yukawa couplings can satisfy all low-energy constraints.

Discovery of $W_R$ at LHC does not rule out leptogenesis.

Abstract

We discuss leptogenesis constraints on the mass of the right-handed $W$-boson ($W_R$) in a TeV-scale Left-Right seesaw model (LRSM) for neutrino masses. For generic Dirac mass of the neutrinos, i.e. with all Yukawa couplings $\lesssim 10^{-5.5}$, it has been pointed out that successful leptogenesis requires a lower bound of 18 TeV on the $W_R$ mass, pushing it beyond the reach of LHC. Such TeV-scale LRSM must, however, be parity-asymmetric for type-I seesaw to give the observed neutrino masses. This class of models can accommodate larger Yukawa couplings, which give simultaneous fits to charged-lepton and neutrino masses, by invoking either cancellations or specific symmetry-textures for Dirac ($M_D$) and Majorana ($M_N$) masses in the seesaw formula. We show that in this case, the leptogenesis bound on $M_{W_R}$ can be substantially weaker, i.e. $M_{W_R}\gtrsim 3$ TeV for $M_N \lesssim M_{W_R}$. This happens due to considerable reduction of the dilution effects from $W_R$-mediated decays and scatterings, while the washout effects due to inverse decays are under control for certain parameter ranges of the Yukawa couplings. We also show that this model is consistent with all other low energy constraints, such as lepton flavor violation and neutrinoless double beta decay. Thus, a discovery of the right-handed gauge bosons alone at the LHC will not falsify leptogenesis as the mechanism behind the matter-antimatter asymmetry in our Universe.