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Singularity-free cosmological solutions in quadratic gravity

P. Kanti·J. Rizos·K. Tamvakis
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Abstract

We study a general field theory of a scalar field coupled to gravity through a quadratic Gauss-Bonnet term $ξ(ϕ) R^2_{GB}$. The coupling function has the form $ξ(ϕ)=ϕ^n$, where $n$ is a positive integer. In the absence of the Gauss-Bonnet term, the cosmological solutions for an empty universe and a universe dominated by the energy-momentum tensor of a scalar field are always characterized by the occurrence of a true cosmological singularity. By employing analytical and numerical methods, we show that, in the presence of the quadratic Gauss-Bonnet term, for the dual case of even $n$, the set of solutions of the classical equations of motion in a curved FRW background includes singularity-free cosmological solutions. The singular solutions are shown to be confined in a part of the phase space of the theory allowing the non-singular solutions to fill the rest of the space. We conjecture that the same theory with a general coupling function that satisfies certain criteria may lead to non-singular cosmological solutions.

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P. Kanti, J. Rizos, K. Tamvakis. 1998-11-22. Singularity-free cosmological solutions in quadratic gravity. https://doi.org/10.1103/physrevd.59.083512

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