Constraining Reheating Temperature, Inflaton-SM Coupling and Dark Matter Mass in Light of ACT DR6 Observations

TL;DR

This paper uses recent ACT DR6 observations combined with other data to constrain inflationary models, reheating parameters, and dark matter mass, incorporating effects like Bose enhancement and gravitational production.

Contribution

It provides new bounds on reheating temperature, inflaton-SM coupling, and dark matter mass within $eta$-attractor inflation models, considering both perturbative and nonperturbative effects.

Findings

Reheating temperature bounds are tightened by ACT data.

Inflaton-SM coupling constraints include Bose enhancement effects.

Dark matter mass ranges are identified consistent with reheating constraints.

Abstract

We explore the phenomenological implications of the latest Atacama Cosmology Telescope (ACT) DR6 observations, in combination with Planck 2018, BICEP/Keck 2018, and DESI, on the physics of inflation and post-inflationary reheating. We focus on the $\alpha$-attractor class of inflationary models (both E- and T-models) and consider two reheating scenarios: perturbative inflaton ($\phi$) decay ($\phi \rightarrow bb$) and inflaton annihilation ($\phi \phi \rightarrow bb$) into Standard Model (SM) bosonic particles ($b$). By solving the Boltzmann equations, we derive bounds on key reheating parameters, including the reheating temperature, the inflaton equation of state (EoS), and the inflaton-SM coupling, in light of ACT data. To accurately constrain the coupling, we incorporate the Bose enhancement effect in the decay width. To ensure the validity of our perturbative approach, we also identify the regime where nonperturbative effects, such as parametric resonance, become significant. Additionally, we include indirect constraints from primordial gravitational waves (PGWs), which can impact the effective number of relativistic species, $\Delta N_{\rm eff}$. These constraints further bound the reheating temperature, particularly in scenarios with a stiff EoS. Finally, we analyze dark matter (DM) production through purely gravitational interactions during reheating and determine the allowed mass ranges consistent with the constrained reheating parameter space and recent ACT data.