Tachyonic cosmology with cubic contractions of the Riemann tensor

TL;DR

This paper introduces a modified gravity cosmological model with a tachyonic field coupled to a topological invariant involving third order Riemann tensor contractions, explaining cosmic acceleration.

Contribution

It proposes a novel tachyonic cosmological model with a specific topological invariant coupling, deriving modified Friedmann and Klein-Gordon equations, and analyzing its dynamics.

Findings

Model explains current accelerated expansion.

Compatible with matter-dominated epoch.

High agreement with recent cosmic history.

Abstract

A new cosmological theory is proposed in the theoretical framework of modified gravity theories which is based on a tachyonic field non-minimally coupled with a specific topological invariant constructed with third order contractions of the Riemann tensor. After proposing the action of the cosmological model, the modified Friedmann relations and the Klein-Gordon equations are obtained, describing the corresponding geometrical corrections to the Einstein-Hilbert action. The physical features of the cosmological system are investigated by adopting the dynamical system analysis in the case of an exponential function for the geometrical coupling term. The investigation revealed that the cosmological system can explain the current accelerated expansion of the Universe and the matter dominated epoch, showing a high compatibility to the recent history of our Universe for various values of the coupling coefficients.