Warm Hybrid Axion Inflation in $\alpha$-Attractor Models Constrained by ACT and Future Plan experiments

TL;DR

This paper investigates warm hybrid axion inflation within $lpha$-attractor models, analyzing its compatibility with current and future CMB data, and finds that observable gravitational waves are predicted across various dissipation regimes, offering testable predictions.

Contribution

It introduces a detailed analysis of warm hybrid axion inflation in $lpha$-attractor models, considering different dissipation regimes and confronting predictions with observational data.

Findings

Weak dissipation predicts $n_s \,\approx\, 0.965$ at the boundary of constraints.

Stronger dissipation yields $n_s$ within 1-2$hi$ confidence regions.

Tensor modes remain observable, enabling future detection of primordial gravitational waves.

Abstract

We present a comprehensive study of warm hybrid inflation within the framework of $\alpha$-attractor models, where an axionic inflaton is coupled to a waterfall field in the presence of thermal dissipation. The model is analyzed for both linear ($\Upsilon \propto T$) and cubic ($\Upsilon \propto T^{3}$) dissipation regimes. Confronting the theoretical predictions with the latest observational data from Planck+BICEP/Keck, P-ACT-LB-BK18 and SPT, and , we find that in the weak dissipative regime ($Q_{*} \lesssim 10^{-5}$), the scalar spectral index $n_{s} \simeq 0.965$ lies at the boundary of the combined P-ACT-LB-BK18 constraints, while the tensor-to-scalar ratio $r$ remains within observable ranges. For stronger dissipation ($Q_{*} \gtrsim 10^{-5}$), the model predicts values of $n_{s}$ well within the $1$--$2\sigma$ confidence region of all datasets, with tensor modes remaining fully observable in both dissipation scenarios. These results indicate that forthcoming CMB polarization experiments may be capable of detecting primordial gravitational waves, thereby providing a robust observational test of warm hybrid inflation across different dissipative regimes.