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arXiv · 1903.05427

Cosmology with subdominant Horndeski scalar field

Nicola Franchini·Thomas P. Sotiriou
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Abstract

We study the cosmological evolution of a scalar field in Horndeski gravity, assuming that the scalar field is subdominant with respect to the cosmic fluid. We first analyse the most general shift-symmetric action that respects local Lorentz symmetry. We show that the bound on the speed of gravitational waves set by GW170817+GRB170817A imposes a constraint only on the linear coupling between the scalar and the Gauss-Bonnet invariant and this constraint is rather mild. Then, we consider some interesting examples of theories that break shift-symmetry, such as the Damour-Esposito-Farèse model of spontaneous scalarization and a theory with a quadratic coupling to the Gauss-Bonnet invariant that can lead to black hole scalarization. In both cases, tuning of cosmological initial conditions is necessary to keep the scalar field dormant during cosmic evolution.

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Nicola Franchini, Thomas P. Sotiriou. 2020-03-30. Cosmology with subdominant Horndeski scalar field. https://doi.org/10.1103/physrevd.101.064068

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