CMB from a Gauss-Bonnet-induced de Sitter fixed point

TL;DR

This paper explores how higher curvature gravitational theories with a nonminimally coupled scalar field can produce de Sitter fixed points that serve as inflationary phases, consistent with cosmological observations and potentially testable by future data.

Contribution

It analyzes the phase space and perturbation spectra of a scalar-tensor theory with Gauss-Bonnet coupling, revealing conditions for inflationary fixed points compatible with observations.

Findings

Fixed points can be sinks or saddles depending on coupling strength.

Perturbation spectra near fixed points can match cosmological data.

Future observations can constrain the model's coupling function.

Abstract

In the gravitational effective theories including higher curvature terms, cosmological solutions can have nontrivial de Sitter fixed points. We study phenomenological implications of such points, focusing on a theory in which a massive scalar field is nonminimally coupled to the Euler density. We first analyze the phase portrait of the dynamical system and show that the fixed point can be a sink or a saddle, depending on the strength of the coupling. Then, we compute the perturbation spectra generated in the vicinity of the fixed point in order to investigate whether the fixed point may be considered as cosmic inflation. We find parameter regions that are consistent with the cosmological data, given that the anisotropies in the cosmic microwave background are seeded by the fluctuations generated near the fixed point. Future observation may be used to further constrain the coupling function of this model. We also comment briefly on the swampland conjecture.