Bayesian Constraints on Inverse-Tangent Inflation with Constant-EOS Reheating and a Dynamical Reheating Analysis

Abstract

We perform a Bayesian inference analysis of an inflationary model based on an inverse-tangent potential, incorporating reheating dynamics in both constant and dynamical equation-of-state (DEOS) frameworks. Using Planck and ACT constraints on the scalar spectral index, we find preferred values $\hat{I}º\simeq 0.5-0.6$ and $N_k\simeq 40-60$, leading to reheating temperatures $T_{RH}\sim 10^{10}-10^{14}$ GeV and reheating durations $N_{RH}\sim 3-36$ e-folds. Reheating weighted $H_0$ posteriors shift the Planck inference towards the ACT preferred region through the intrinsic $n_s-H_0$ degeneracy of the CMB likelihood. In the DEOS framework, reheating with a constant decay rate yields $N_{RH}\simeq 4-8$ e-folds and $T_{RH}\simeq 10^{13}$ GeV, while a dynamical decay rate produces a strong dependence on the Yukawa coupling $y$, with $N_{RH}$ varying from $\mathcal{O}(30)$ to $\mathcal{O}(1)$ e-folds and the reheating temperature spanning $\sim 10^{-2}-10^{14}$ GeV. Imposing inflation-reheating consistency significantly restricts the viable parameter space to a narrow region around $n_s\simeq 0.9720-0.9725$ and $r\simeq 0.026-0.060$, demonstrating that reheating dynamics provide a nontrivial bridge between early-universe inflation and late-time cosmological parameter inference.

18 pages, 8 figures, 3 tables