The magnetic universe in the theory of gravity with non-minimal kinetic coupling of a scalar field

Abstract

In this paper, we obtain cosmological solutions within the framework of Bianchi I model with a unidirectional magnetic field in the theory of gravity with non-minimum kinetic coupling of a scalar field with curvature ($η\cdot(ϕ/2)\cdot G_{μν}\,\nabla^μ\nabla^νϕ$). We believe that the solutions are applicable to the period before and during primary inflation. In the previous work [R. K. Muharlyamov, T. N. Pankratyeva, S. O. A. Bashir, JCAP05(2025)018] we considered such a problem for a special case -- the locally rotationally symmetric Bianchi I space-time ($a_1=a_2$). Here we generalize the results for different scale factors $a_1\neq a_2 \neq a_3$. There are distinctive properties of the models and a number of interesting properties are preserved. The main conclusion remains valid. For $l=1+\varepsilonηΛ/μ>0$, the model has the necessary properties: isotropization during expansion, rapid transition to inflationary expansion, absence of ghost and Laplace instabilities. Here, $Λ$ is the cosmological constant, $μ=M^2_{PL}$ is the Planck mass squared, the sign $\varepsilon=\pm 1$ defines the canonical scalar field and the phantom field, respectively. The differences in the model appear in the neighborhood of the starting point and at times of several units $h_η\cdot t$ from it ($h_η=\sqrt{\frac{\varepsilon}{3η}}$). In the previous model with $l>0$, the Universe is described by the Kasner metric in the neighborhood of the initial point. In the generalized model, there is no the Kasner metric. In the presented model, the anisotropy level is a non-monotonic function. There is a rebound point on the plot. This is the non-standard behavior. But, in the end, the process of isotropization occurs.