Cosmological Signatures of Neutrino Seesaw Mechanism

Abstract

The tiny neutrino masses are most naturally explained by seesaw mechanism through singlet right-handed neutrinos, which can further explain the matter-antimatter asymmetry in the Universe. In this Letter, we propose a new approach to study cosmological signatures of neutrino seesaw through the interaction between inflaton and right-handed neutrinos that respects the shift symmetry. In our framework, after inflation the inflaton predominantly decays into right-handed neutrinos and its decay rate is modulated by the fluctuations of Higgs field that act as the source of curvature perturbations. This gives a new realization of Higgs modulated reheating, and it produces primordial non-Gaussian signatures that can be measured by the forthcoming large-scale structure surveys. We find that these surveys have the potential to probe a large portion of the neutrino seesaw parameter space, opening up a new window for testing the high scale seesaw mechanism.

Figures (2)

• Figure 1: Prediction of the non-Gaussianity (NG) $f_{\rm{NL}}^{\rm{local}}$ from the seesaw parameter space of the heavy neutrino mass scale $M$ versus Yukawa coupling $y_\nu^{}\space$.
• Figure 2: Prediction of the non-Gaussianity $f_{\rm{NL}}^{\rm{local}}$ from the seesaw parameter space of heavy neutrino mass scale $M$ versus the Yukawa coupling $y_\nu^{}\space$, where we input the SM Higgs self-coupling $\lambda\!=\!0.01\space$ (solid curves) and $\lambda\!=\!0.02\space$ (dashed curves), and the Hubble parameter during inflation is set as $H_\text{inf}^{}\!=\!10^{13}\text{GeV}$ and $3\!\times\! 10^{13}\text{GeV}$ respectively.