Reconstruction in the Horndeski theory within the scope of the Bianchi I cosmology

TL;DR

This paper extends a reconstruction method for scalar-tensor theories to anisotropic Bianchi I cosmology within the Horndeski class, enabling realistic modeling of anisotropic universe evolution and stability analysis.

Contribution

It develops a reconstruction approach for Horndeski theories in Bianchi I spacetime, incorporating anisotropy through a chosen kinetic function and analyzing stability.

Findings

Reconstruction of scalar field models with anisotropy is demonstrated.

The method allows modeling of post-inflationary transition to radiation dominance.

Models are shown to be free of ghosts and Laplacian instabilities.

Abstract

In the previous article Eur. Phys. J. Plus 136, 590 (2021) (arXiv: 2110.15396) we have proposed a reconstruction method for the kinetic gravity braiding theory in the framework of the flat Friedman-Robertson-Walker spacetime. Here we develop this method in the Bianchi I spacetime model for a subclass of the Horndeski theory: $G_5 \sim \phi $, $G_2(X)\neq0$, $G_3(X)\neq0$. The Hubble parameter $H(t)$ and the canonical kinetic term $X(t)$ are set a priori. The choice of the function $X(t)$ determines the anisotropic properties of the Universe. This makes it possible to provide believable anisotropy. The presented method allows for a realistic model of the Universe to simply reconstruct some scalar field theory. Reconstruction example is given for anisotropic model of a post-inflationary transition to the radiation-dominated phase. The model is investigated for the absence ghosts and Laplacian instabilities.