R^2-inflation with conformal SM Higgs field

TL;DR

This paper explores a modified R^2-inflation model where the Standard Model Higgs field is conformally coupled to gravity, leading to lower reheating temperatures, altered inflation predictions, and distinctive gravitational wave signals detectable by future experiments.

Contribution

It introduces conformal coupling of the Higgs to gravity in R^2-inflation, calculates perturbation amplitudes at next-to-leading order, and discusses observable gravitational wave features.

Findings

Lower reheating temperature due to scalaron decay into gluons

Modified scalar and tensor perturbation predictions compared to original models

Distinct gravitational wave signatures potentially observable by BBO and DECIGO

Abstract

We introduce conformal coupling of the Standard Model Higgs field to gravity and discuss the subsequent modification of $R^2$-inflation. The main observation is a lower temperature of reheating which happens mostly through scalaron decays into gluons due to the conformal (trace) anomaly. This modifies all predictions of the original $R^2$-inflation. To the next-to-leading order in slow roll parameters we calculate amplitudes and indices of scalar and tensor perturbations produced at inflation. The results are compared to the next-to-leading order predictions of $R^2$-inflation with minimally coupled Higgs field and of Higgs-inflation. We discuss additional features in gravity wave signal that may help to distinguish the proposed variant of $R^2$-inflation. Remarkably, the features are expected in the region available for study at future experiments like BBO and DECIGO. Finally, we check that (meta)stability of electroweak vacuum in the cosmological model is consistent with recent results of searches for the Higgs boson at LHC.