Testing the Seesaw Mechanism and Leptogenesis with Gravitational Waves.

Jeff A Dror,Graham White,Kazunori Kohri,Hitoshi Murayama,Takashi Hiramatsu

doi:10.1103/physrevlett.124.041804

Abstract

We present the possibility that the seesaw mechanism with thermal leptogenesis can be tested using the stochastic gravitational background. Achieving neutrino masses consistent with atmospheric and solar neutrino data, while avoiding nonperturbative couplings, requires right handed neutrinos lighter than the typical scale of grand unification. This scale separation suggests a symmetry protecting the right-handed neutrinos from getting a mass. Thermal leptogenesis would then require that such a symmetry be broken below the reheating temperature. We enumerate all such possible symmetries consistent with these minimal assumptions and their corresponding defects, finding that in many cases, gravitational waves from the network of cosmic strings should be detectable. Estimating the predicted gravitational wave background, we find that future space-borne missions could probe the entire range relevant for thermal leptogenesis.

Highlights

We present the possibility that the seesaw mechanism with thermal leptogenesis can be tested using the stochastic gravitational background
Estimating the predicted gravitational wave background, we find that future space-borne missions could probe the entire range relevant for thermal leptogenesis
The type-I seesaw, new standard model (SM)-singlet fermions are introduced whose masses are much higher than the electroweak scale—a natural possibility as they are not forbidden by any symmetry

Summary

Testing the Seesaw Mechanism and Leptogenesis with Gravitational Waves

We present the possibility that the seesaw mechanism with thermal leptogenesis can be tested using the stochastic gravitational background. Achieving neutrino masses consistent with atmospheric and solar neutrino data, while avoiding nonperturbative couplings, requires right handed neutrinos lighter than the typical scale of grand unification. Thermal leptogenesis would require that such a symmetry be broken below the reheating temperature We enumerate all such possible symmetries consistent with these minimal assumptions and their corresponding defects, finding that in many cases, gravitational waves from the network of cosmic strings should be detectable. The anomalous violation of baryon and lepton numbers in the standard model partially converts the negative lepton asymmetry to the positive baryon asymmetry This scenario is called thermal leptogenesis [5]. For the seesaw mechanism to have at least one neutrino with mass mν ≳ 0.1 eV and the Yukawa coupling remaining perturbative below the grand unified theory (GUT)

Published by the American Physical Society

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