English

Cosmological models with arbitrary spatial curvature in the theory of gravity with non-minimal derivative coupling

General Relativity and Quantum Cosmology 2023-06-02 v1

Abstract

We investigate isotropic and homogeneous cosmological scenarios in the scalar-tensor theory of gravity with non-minimal derivative coupling of a scalar field to the curvature given by the term (ζ/H02)Gμνμϕνϕ(\zeta/H_0^2) G^{\mu\nu}\nabla_\mu\phi \nabla_\nu\phi in the Lagrangian. In general, a cosmological model is determined by six dimensionless parameters: the coupling parameter ζ\zeta, and density parameters Ω0\Omega_0 (cosmological constant), Ω2\Omega_2 (spatial curvature term), Ω3\Omega_3 (non-relativistic matter), Ω4\Omega_4 (radiation), Ω6\Omega_6 (scalar field term), and the universe evolution is described by the modified Friedmann equation. In the case ζ=0\zeta=0 (no non-minimal derivative coupling) and Ω6=0\Omega_6=0 (no scalar field) one has the standard Λ\LambdaCDM-model, while if Ω60\Omega_6\not=0 -- the Λ\LambdaCDM-model with an ordinary scalar field. The situation is crucially changed when the scalar field possesses non-minimal derivative coupling to the curvature, i.e. when ζ0\zeta\not=0. Now, depending on model parameters, (i) There are three qualitatively different initial state of the universe: an eternal kinetic inflation, an initial singularity, and a bounce. The bounce is possible for all types of spatial geometry of the homogeneous universe; (ii) For all types of spatial geometry, the universe goes inevitably through the primary quasi-de Sitter (inflationary) epoch when a(t)ehdS(H0t)a(t)\propto e^{h_{dS}(H_0t)} with the de Sitter parameter hdS2=1/9ζ8ζΩ23/27Ω6h_{dS}^2={1}/{9\zeta}-{8\zeta\Omega_2^3}/{27\Omega_6}. The mechanism of primary or kinetic inflation is provided by non-minimal derivative coupling and needs no fine-tuned potential; (iii) There are cyclic scenarios of the universe evolution with the non-singular bounce at a minimal value of the scale factor, and a turning point at the maximal one; (iv) There is a natural mechanism providing a change of cosmological epochs.

Keywords

Cite

@article{arxiv.2306.00611,
  title  = {Cosmological models with arbitrary spatial curvature in the theory of gravity with non-minimal derivative coupling},
  author = {Sergey V. Sushkov and Rafkat Galeev},
  journal= {arXiv preprint arXiv:2306.00611},
  year   = {2023}
}