ACT inflation and its influence on reheating era in Einstein-Gauss-Bonnet gravity

TL;DR

The paper tests the observational viability of a non-minimally coupled scalar-Einstein-GB gravity model against ACT-DR6+Planck18+BAO data, focusing on both the inflationary epoch and the subsequent reheating era. By adopting exponential forms for the inflationary potential and Gauss-Bonnet coupling, and matching to reheating forms, the authors derive the inflationary observables $n_s$ and $r$ and show consistency with ACT data for a restricted e-fold range $N_f\in[55,65]$, notably with parameters $\lambda=-0.008$ and $\eta=1$. The reheating analysis reveals that ACT data disfavors $w_{\mathrm{eff}}<1/3$, requiring $N_{\mathrm{re}}>0$ and linking the reheating temperature $T_{\mathrm{re}}$ to the inflationary $N_f$ via $T_{\mathrm{re}} \gtrsim T_{\mathrm{BBN}}$. Overall, ACT data constrain both inflationary dynamics and the subsequent reheating phenomenology in this higher-curvature gravity context, with implications for primordial gravitational waves and late-time consistency with GW170817-era physics.

Abstract

We investigate the observational viability of non-minimally coupled scalar-Einstein-Gauss-Bonnet (GB) gravity, during inflation and post-inflationary reheating dynamics, from the perspective of the latest ACT-DR6 combined with the Planck 2018 and BAO data. It turns out that the ACT result considerably affects the inflationary e-fold number compared to the case where only Planck 2018 data is taken into account. The viable parameter spaces corresponding to the inflationary ACT-DR6+Planck18+BAO substantially influence the reheating phenomenology via the reheating equation of state ($w_\mathrm{eff}$) and the reheating temperature. In particular, the ACT-DR6+Planck18+BAO data seems to disfavor $w_\mathrm{eff} < 1/3$ during the reheating stage, which is unlike to that of only Planck 2018 case. These reveal how the ACT-DR6 data hits the early universe phenomenology from inflation to reheating in the context of higher curvature like scalar-Einstein-GB theory of gravity.

Figures (2)

• Figure 1: Parametric plot of $n_s$ vs. $r$ with $\lambda = -0.008$ and $\eta = 1$, in which case, the $n_s$ and $r$ get simultaneously compatible with the Panck data for $N_\mathrm{f} = [55,65]$.
• Figure 2: Left Plot: $N_\mathrm{re}$ vs. $N_\mathrm{f}$; Right Plot: $T_\mathrm{re}$ (in GeV unit) vs. $N_\mathrm{f}$ for various values of $w_\mathrm{eff}$. In both the plots, we consider $\lambda = -0.005$$\eta = 1$ and $V_0 = 10^{-12}$ (in Planck units). The reheating EoS parameter is taken as $w_\mathrm{eff} = 0 ~(\mathrm{Black~curve}), \frac{1}{6}~(\mathrm{Blue~curve}), \frac{1}{2}~(\mathrm{Magenta~curve}), \frac{2}{3}~(\mathrm{Green~curve}), 1~(\mathrm{Red~curve})$ respectively. Moreover the yellow curve in the right plot is the BBN temperature $\sim 10^{-2}\mathrm{GeV}$. In both the plots, we take $\lambda = -0.008$ and $\eta = 1$, same as in the inflationary case.