Neutron star sensitivities in Hořava gravity after GW170817

Enrico Barausse

doi:10.1103/PhysRevD.100.084053

paper

Neutron star sensitivities in Hořava gravity after GW170817

arXiv:1907.05958 · doi:10.1103/PhysRevD.100.084053

Abstract

Hořava gravity breaks boost invariance in the gravitational sector by introducing a preferred time foliation. The dynamics of this preferred slicing is governed, in the low-energy limit suitable for most astrophysical applications, by three dimensionless parameters $α$ , $β$ and $λ$ . The first two of these parameters are tightly bound by solar system and gravitational wave propagation experiments, but $λ$ remains relatively unconstrained ( $0 \leq λ ≲ 0.01 - 0.1$ ). We restrict here to the parameter space region defined by $α = β = 0$ (with $λ$ kept generic), which in a previous paper we showed to be the only one where black hole solutions are non-pathological at the universal horizon, and we focus on possible violations of the strong equivalence principle in systems involving neutron stars. We compute neutron star 'sensitivities', which parametrize violations of the strong equivalence principle at the leading post-Newtonian order, and find that they vanish identically, like in the black hole case, for $α = β = 0$ and generic $λ \neq = 0$ . This implies that no violations of the strong equivalence principle (neither in the conservative sector nor in gravitational wave fluxes) can occur at the leading post-Newtonian order in binaries of compact objects, and that data from binary pulsars and gravitational interferometers are unlikely to further constrain $λ$ .

arXiv comment10 pages, no figures. Improved discussion to match version accepted for publication in PRD. v3: Typos corrected in proof; v2: typos in Eqs 16 and 23b corrected in erratum (typos do not propagate, results unchanged)

Neutron star sensitivities in Hořava gravity after GW170817

Abstract

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