Leptogenesis and neutral gauge bosons

Abstract

We consider low-scale leptogenesis via right-handed neutrinos $N$ coupled to a $Z^{\prime }$ boson, with gauged $U(1{)}_{B-L}$ as a simple realization. Keeping the neutrinos sufficiently out of equilibrium puts strong bounds on the $Z^{\prime }$ coupling strength and mass, our focus being on light $Z^{\prime }$ and $N$, testable in the near future by SHiP, HPS, Belle II, and at the LHC. We show that leptogenesis could be robustly falsified in a large region of parameter space by the double observation of $Z^{\prime }$ and $N$, e.g. in the channel $pp\to Z^{\prime }\to NN$ with displaced $N$-decay vertex, and by several experiments searching for light $Z^{\prime }$, according to the mass of $N$.

Comments: 9 pages, 8 figures; added one figure and minor clarifications, matches PRD version