## Early universe cosmological solutions in exponential gravity

### Abstract

In this work we present some cosmologically relevant solutions using the spatially flat Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime in metric $f(R)$ gravity where the form of the gravitational Lagrangian is given by $\frac{1}{\alpha}e^{\alpha R}$. In the low curvature limit this theory reduces to ordinary Einstein-Hilbert Lagrangian together with a cosmological constant term. Precisely because of this cosmological constant term this theory of gravity is able to support nonsingular bouncing solutions in both matter and vacuum background. Since for this theory of gravity $f^{\prime}$ and $f^{\prime\prime}$ is always positive, this is free of both ghost instability and tachyonic instability. Moreover, because of the existence of the cosmological constant term, this gravity theory also admits a de-Sitter solution. Lastly we hint towards the possibility of a new type of cosmological solution that is possible only in higher derivative theories of gravity like this one.Comment: 22 pages, 20 figures. Some new material on cosmological perturbation is added and the introduction section has slightly been modified. Some new figures are included. Accepted for publication in the special issue on "Bounce Cosmology" in Universe-Open Access Journal of Theoretical Physics. arXiv admin note: text overlap with arXiv:1610.00938 by other author

Topics: General Relativity and Quantum Cosmology, Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Theory
Year: 2018
OAI identifier: oai:arXiv.org:1805.06673

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