Scalar-tensor theories and modified gravity in the wake of GW170817

David Langlois (1) , Ryo Saito (2) , Daisuke Yamauchi (3) , Karim Noui (4)

1 APC (UMR_7164) - AstroParticule et Cosmologie
2 Yamaguchi University [Yamaguchi]
3 Kanagawa University
4 LMPT - Laboratoire de Mathématiques et Physique Théorique

Theories of dark energy and modified gravity can be strongly constrained by astrophysical or cosmological observations, as illustrated by the recent observation of the gravitational wave event GW170817 and of its electromagnetic counterpart GRB 170817A, which showed that the speed of gravitational waves, cg, is the same as the speed of light, within deviations of order 10$^{-15}$. This observation implies severe restrictions on scalar-tensor theories, in particular theories whose action depends on second derivatives of a scalar field. Working in the very general framework of degenerate higher-order scalar-tensor (DHOST) theories, which encompass Horndeski and beyond Horndeski theories, we present the DHOST theories that satisfy cg=c. We then examine, for these theories, the screening mechanism that suppresses scalar interactions on small scales, namely the Vainshtein mechanism, and compute the corresponding gravitational laws for a nonrelativistic spherical body. We show that it can lead to a deviation from standard gravity inside matter, parametrized by three coefficients which satisfy a consistency relation and can be constrained by present and future astrophysical observations.

Mots clés: screening: Vainshtein; gravitation: model; field theory: scalar; interaction: scalar; gamma ray: burst; photon: velocity; scalar tensor; cosmological model; gravitational radiation: emission; gravitational radiation: direct detection; gravitational radiation detector; nonrelativistic; electromagnetic field: production; higher-order; dark energy

Domaines: Relativité Générale et Cosmologie Quantique [gr-qc]

David Langlois, Ryo Saito, Daisuke Yamauchi, Karim Noui. Scalar-tensor theories and modified gravity in the wake of GW170817. Physical Review D, 2018, 97 (6), pp.061501. ⟨10.1103/PhysRevD.97.061501⟩. ⟨hal-01758722⟩