Light inflaton model in a metastable Universe

TL;DR

This paper proposes a minimal extension of the Standard Model with a scalar inflaton that can reheat the universe and is consistent with a metastable vacuum, exploring its parameter space and experimental prospects.

Contribution

It introduces a Z2 symmetric inflaton-Higgs model that naturally allows a metastable universe without fine-tuning, and analyzes its experimental detectability.

Findings

Inflaton masses range from 10^-3 to the Higgs mass.

Mixing angles span from 10^-11 to 10^-2.

Current experiments can probe mixing angles above 10^-4.

Abstract

We minimally extend the SM with a Z$_2$ symmetric potential containing a single scalar field, serving as our inflaton with a quartic self-coupling. In the model we have symmetry breaking in both sectors, and with the addition of an inflaton-Higgs portal, the Universe is able to efficiently reheat via 2-2 inflaton-Higgs scattering. Assuming that the Universe with a positive cosmological constant should be metastable, only one particular symmetry breaking pattern in the vacuum is possible, without the need to finely-tune the Higgs' quartic self-coupling. Inflaton with masses in the range $O(10^{-3})\leq m_{\chi}\leq m_{h}$ and mixing angles that span $\theta_{m}^{2}=O(10^{-11}-10^{-2})$ evade all current cosmological, experimental and stability constraints required for a metastable EW vacuum. Upgraded particle physics experiments may be able to probe the parameter space with $\theta_{m}^{2}\geq O(10^{-4})$, where we would observe trilinear Higgs couplings suppressed by up to $2\%$ compared to the SM value. However to access the parameter space of very weakly-coupled inflaton, we rely on the proposals to build experiments that target the hidden sector.