Primordial non-Gaussianity as a probe of seesaw and leptogenesis

A bstract We present the possibility that the seesaw mechanism and nonthermal leptogenesis can be investigated via primordial non-Gaussianities in the context of a majoron curvaton model. Originating as a massless Nambu-Goldstone boson from the spontaneous breaking of the global baryon ( B ) minus lepton ( L ) number symmetry at a scale v B−L , majoron becomes massive when it couples to a new confining sector through anomaly. Acting as a curvaton, majoron produces the observed red-tilted curvature power spectrum without relying on any inflaton contribution, and its decay in the post-inflationary era gives rise to a nonthermal population of right-handed neutrinos that participate in leptogenesis. A distinctive feature of the mechanism is the generation of observable non-Gaussianity, in the parameter space where the red-tilted power spectrum and sufficient baryon asymmetry are produced. We find that the non-Gaussianity parameter f NL ≳ O (0 . 1) is produced for high-scale seesaw ( v B−L at O (10 14 − 17 ) GeV) and leptogenesis ( M 1 ≳ O (10 6 ) GeV) where the latter represents the lightest right-handed neutrino mass. While the current bounds on local non-Gaussianity excludes some part of parameter space, the rest can be fully probed by future experiments like CMB-S4, LSST, and 21 cm tomography.