Anisotropy screening in Horndeski cosmologies

Abstract

We consider anisotropic cosmologies in a particular shift-symmetric Horndeski theory containing the $G^{\mu \nu }{\partial }_{\mu }\varphi {\partial }_{\nu }\varphi$ coupling, where $G^{\mu \nu }$ is the Einstein tensor. This theory admits stable in the future self-accelerating cosmologies whose tensor perturbations propagate with the velocity very close to the speed of light such that the theory agrees with the gravity wave observations. Surprisingly, we find that the anisotropies within the Bianchi I homogeneous spacetime model are screened at early time by the scalar charge, whereas at late times they are damped in the usual way. Therefore, contrary to what one would normally expect, the early state of the universe in the theory cannot be anisotropic and (locally) homogeneous in the absence of spatial curvature. The early universe cannot be isotropic either, because it should then be unstable with respect to inhomogeneous perturbations. As a result, the early universe should be inhomogeneous. At the same time, we find that in the spatially curved Bianchi IX case the anisotropies can be strong at early times even in the presence of a scalar charge.

arXiv comment18 pages, 2 figures, matches the published version

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• Microphysical manifestations of viscosity and consequences for anisotropies in the very early universe
• More on the first-order thermodynamics of scalar-tensor and Horndeski gravity
• Constraints on dark energy models from the Horndeski theory
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• Bianchi I metric solutions with nonminimally coupled Einstein-Maxwell gravity theory
• Stable small spatial hairs in a power-law k-inflation model
• Anisotropic chiral cosmology: exact solutions
• Anisotropic hyperbolic inflation for a model of two scalar and two vector fields
• Anti-de Sitter neutron stars in the theory of gravity with nonminimal derivative coupling
• Reconstruction in the Horndeski theory within the scope of the Bianchi I cosmology
• Bianchi IX geometry and the Einstein-Maxwell theory
• Generalized Horndeski-Like Einstein Gauss-Bonnet Inflation with Massless Primordial Gravitons
• Fab-Four cosmography to tackle the Hubble tension
• The nonlinear anisotropic model of the Universe with the linear potential
• Anisotropic power-law inflation for models of non-canonical scalar fields non-minimally coupled to a two-form field
• Perturbations in Horndeski theory above anisotropic cosmological background
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• Anisotropic power-law inflation for the Sáez-Ballester theory non-minimally coupled to a vector field
• Exact cosmological solutions with magnetic field in the theory of gravity with non-minimal kinetic coupling
• Horndeski in motion
• Power-law Bianchi type I inflation with multiple vector fields
• Exact Dynamical Black Hole Solutions in Five or Higher Dimensions
• Intermediate inflation in generalized non-minimal derivative coupling model