Relic gravity waves and 7 keV dark matter from a GeV scale inflaton

F.L Bezrukov,D.S Gorbunov

doi:10.1016/j.physletb.2014.07.060

Abstract

We study the mechanism of generation of 7 keV sterile neutrino Dark Matter (DM) in the model with light inflaton χ, which serves as a messenger of scale invariance breaking. In this model the inflaton, in addition to providing reheating to the Standard Model (SM) particles, decays directly into sterile neutrinos. The latter are responsible for the active neutrino oscillations via seesaw type I mechanism. While the two sterile neutrinos may also produce the lepton asymmetry in the primordial plasma and hence explain the baryon asymmetry of the Universe, the third one being the lightest may be of 7 keV and serve as DM. For this mechanism to work, the mass of the inflaton is bound to be light (0.1–1 GeV) and uniquely determines its properties, which allows to test the model. For particle physics experiments these are: inflaton lifetime (10−5–10−12 s), branching ratio of B-meson to kaon and inflaton (10−6–10−4) and inflaton branching ratios into light SM particles like it would be for the SM Higgs boson of the same mass. For cosmological experiments these are: spectral index of scalar perturbations (ns≃0.957–0.967), and amount of tensor perturbations produced at inflation (tensor-to-scalar ratio r≃0.15–0.005).

Highlights

Discovery of the neutral scalar with properties very close to what we expect for the Standard Model (SM) Higgs boson [1,2] and absence of any definite hints of supersymmetry at LHC asks for its replacement as a solution to gauge hierarchy problem
Some hope is associated with conformal or scale invariance that might be a symmetry of the SM at tree level, but for the only dimensionful parameter of the SM v which gives the vacuum expectation value to the Englert–Brout–Higgs (EBH) field
With only one dimensionful parameter explicitly breaking scale invariance in the inflaton sector, the model is consistent with cosmological observations [6] and constraints from particle physics related to the possible manifestation of the light inflaton in B-meson decays [5]

Summary

Introduction

Discovery of the neutral scalar with properties very close to what we expect for the SM Higgs boson [1,2] and absence of any definite hints of supersymmetry at LHC asks for its replacement as a solution to gauge hierarchy problem. Which can be considered as a messenger of the scale symmetry breaking, exact mechanism of this breaking is beyond the present analysis This means that we assumed that other dimensionful parameters, like Higgs boson mass term or cubic terms in the potential are small and can be neglected. With only one dimensionful parameter explicitly breaking scale invariance in the inflaton sector, the model is consistent with cosmological observations [6] and constraints from particle physics related to the possible manifestation of the light inflaton in B-meson decays [5]. Four parameters of the model, mX , β, λ, and α, determine the EBH field vacuum expectation value v ≈ 246 GeV, the Higgs boson mass mh ≈ 126 GeV [1,2], and the inflaton mass β β mχ = mh. We show below that the first two are automatically satisfied with the parameters, leading to the proper DM generation, and the latter one leads to significant bound on the inflaton mass mχ (and effective upper bound on r)

Dark matter generation

Summary