Constraining scalar-Gauss-Bonnet Inflation by Reheating, Unitarity and PLANCK

TL;DR

This paper analyzes scalar-Gauss-Bonnet inflation models in light of Planck data, constraining parameters through reheating and unitarity considerations, and finds significant restrictions on the coupling parameters, especially for quadratic couplings.

Contribution

It provides new constraints on inflaton-Gauss-Bonnet coupling parameters using reheating and unitarity, refining the viable parameter space for these inflation models.

Findings

Reheating and unitarity significantly restrict the parameter space.

Quadratic Gauss-Bonnet coupling is more strongly constrained than linear.

Higgs inflation with Gauss-Bonnet term is strongly disfavored.

Abstract

We revisit the inflationary dynamics in detail for theories with Gauss-Bonnet gravity coupled to scalar functions, in light of the Planck data. Considering the chaotic inflationary scenario, we constrain the parameters of two models involving inflaton-Gauss-Bonnet coupling by current Planck data. For non zero inflaton-Gauss-Bonnet coupling $\beta$, an inflationary analysis provides us a big cosmologically viable region in the space of $(m,\beta)$, where $m$ is the mass of inflaton. However, we study further on constraining $\beta$ arising from reheating considerations and unitarity of tree-level amplitude involving we have studied the constraints on $\beta$ arising from reheating considerations and unitarity of tree level amplitude involving $2$ graviton $\rightarrow 2$ graviton ($h h\rightarrow hh$) scattering. Our analysis, particularly on reheating significantly reduces the parameter space of $(m,\beta)$ for all models. he quadratic Gauss-Bonnet coupling parameter turns out to be more strongly constrained than that of the linear coupling. For the linear Gauss-Bonnet coupling function, we obtain $\beta \lesssim 10^3$, with the condition $\beta (m/M_P)^2 \simeq 10^{-4}$. However, study of the Higgs inflation scenario in the presence of Gauss-Bonnet term turned out to be strongly disfavored.