The nonlinear anisotropic model of the Universe with tadpole

Some subclasses of Horndeski theory allow for non-standard behavior of anisotropy in the homogeneous Bianchi I cosmology. For example, the anisotropy are damped near the initial singularity instead of tending to infinity. In this article, we analyze nonlinear anisotropic models with a tadpole term. We have considered an example of such a theory for which the anisotropy is maximal and finite at the initial moment of time and approaches zero at later times. The anisotropy suppression occurs during the inflationary stage. This cosmological model does not contain a singular point

Axion-induced oscillations of cooperative electric field in a cosmic magneto-active plasma

We consider one cosmological application of an axionic extension of the Maxwell-Vlasov theory, which describes axionically induced oscillatory regime in the state of global magnetic field evolving in the anisotropic expanding (early) universe. We show that the cooperative electric field in the relativistic plasma, being coupled to the pseudoscalar (axion) and global magnetic fields, plays the role of a regulator in this three-level system; in particular, the cooperative (Vlasov) electric field converts the regime of anomalous growth of the pseudoscalar field, caused by the axion-photon coupling at the inflationary epoch of the universe expansion, into an oscillatory regime with finite density of relic axions. We analyze solutions to the dispersion equations for the axionically induced cooperative oscillations of the electric field in the relativistic plasma.Comment: 7 pages, misprints correcte

Electromagnetic waves in an axion-active relativistic plasma non-minimally coupled to gravity

We consider cosmological applications of a new self-consistent system of equations, accounting for a nonminimal coupling of the gravitational, electromagnetic and pseudoscalar (axion) fields in a relativistic plasma. We focus on dispersion relations for electromagnetic perturbations in an initially isotropic ultrarelativistic plasma coupled to the gravitational and axion fields in the framework of isotropic homogeneous cosmological model of the de Sitter type. We classify the longitudinal and transversal electromagnetic modes in an axionically active plasma and distinguish between waves (damping, instable or running), and nonharmonic perturbations (damping or instable). We show that for the special choice of the guiding model parameters the transversal electromagnetic waves in the axionically active plasma, nonminimally coupled to gravity, can propagate with the phase velocity less than speed of light in vacuum, thus displaying a possibility for a new type of resonant particle-wave interactions.Comment: 19 pages, 9 figures, published versio

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

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