Cosmology with nonminimal kinetic coupling and a power-law potential

TL;DR

This paper explores cosmological models with a scalar field nonminimally coupled to gravity via kinetic terms and a power-law potential, revealing unique inflationary behaviors influenced solely by the coupling parameter.

Contribution

It introduces a dynamical system analysis of nonminimal kinetic coupling models with power-law potentials, highlighting new inflationary regimes independent of the potential shape.

Findings

Existence of quasi-de Sitter inflation for 0<N<2 driven by kinetic coupling.

Identification of two late-time regimes: power-like expansion and secondary inflation.

Kinetic coupling inflation is impossible for potentials with N>2.

Abstract

We consider cosmological dynamics in the theory of gravity with the scalar field possessing a nonminimal kinetic coupling to gravity, $\kappa G_{\mu\nu}\phi^{\mu}\phi^{\nu}$, and the power-law potential $V(\phi)=V_0\phi^N$. Using the dynamical system method, we analyze all possible asymptotical regimes of the model under investigation and show that for sloping potentials with $0<N<2$ there exists a quasi-de Sitter asymptotic $H={1}/{\sqrt{9\kappa}}$ corresponding to an early inflationary Universe. In contrast to the standard inflationary scenario, the kinetic coupling inflation does not depend on a scalar field potential and is only determined by the coupling parameter $\kappa$. We obtain that there exist two different late-time asymptotical regimes. The first one leads to the usual power-like cosmological evolution with $H=1/3t$, while the second one represents the late-time inflationary Universe with $H=1/\sqrt{3\kappa}$. This secondary inflationary phase depends only on $\kappa$ and is a specific feature of the model with nonminimal kinetic coupling. Additionally, an asymptotical analysis shows that for the quadric potential with N=2 the asymptotical regimes remain qualitatively the same, while the kinetic coupling inflation is impossible for steep potentials with N>2. Using a numerical analysis, we also construct exact cosmological solutions and find initial conditions leading to the initial kinetic coupling inflation followed either by a "graceful" oscillatory exit or by the secondary inflation.