Light inflaton after LHC8 and WMAP9 results

TL;DR

The paper addresses the tension between a simple quartic chaotic inflaton and current cosmological data by introducing a small non-minimal coupling to gravity and a light inflaton that mixes with the SM Higgs. It analyzes the inflationary dynamics in the Einstein frame, derives slow-roll predictions and the dependence of $r$ and $n_s$ on the non-minimal coupling $\xi$, and fixes the quartic coupling $\beta$ from the primordial amplitude, while accounting for reheating via Higgs production. The authors study the resulting phenomenology, showing that the inflaton can be produced in $B$-meson decays with lifetimes that yield missing energy, displaced vertices, or resonant signatures in three-body decays, and identify the mass window $\sim$300 MeV–a few GeV as testable at $B$-factories, Belle-II, and LHCb; CHARM and Dalitz analyses provide further constraints. They also discuss extensions to a νMSM framework, where the inflaton can contribute to dark matter production and baryogenesis, thus linking early Universe inflation to low-energy experiments and cosmological observations.

Abstract

We update the allowed parameter space of the simple chaotic inflationary model with quartic potential and light inflaton [Bezrukov,Gorbunov'2009] taking into account recent results from cosmology (CMB observations from SPT, ACT and WMAP) and from particle physics (LHC hints of the SM Higgs boson). The non-minimal (yet small) coupling to gravity of the inflaton becomes essential to fit the observational data. The inflaton has mass above 300 MeV and can be searched for at B-factories in B-meson two-body decays to kaon and inflaton. The inflaton lifetime depends on the model parameters, resulting in various inflaton signatures: either a missing energy, or a displaced vertex from the B-meson decay position, or a resonance in the Dalitz plot of a three particle decay. We also discuss the implementation of the inflaton model to the nuMSM, where the inflaton can be responsible for production of the dark matter sterile neutrino in the early Universe.