Neutron star sensitivities in Hořava gravity after GW170817

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 $\alpha$, $\beta$ and $\lambda$. The first two of these parameters are tightly bound by solar system and gravitational wave propagation experiments, but $\lambda$ remains relatively unconstrained ($0\le \lambda \lesssim 0.01-0.1$). We restrict here to the parameter space region defined by $\alpha =\beta =0$ (with $\lambda$ 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 $\alpha =\beta =0$ and generic $\lambda \ne 0$. 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 $\lambda$.

10 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)

References in corpus (12)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• The Confrontation between General Relativity and Experiment
• Multi-messenger Observations of a Binary Neutron Star Merger
• Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
• Quantum Gravity at a Lifshitz Point
• Models of non-relativistic quantum gravity: the good, the bad and the healthy
• Matter-gravity couplings and Lorentz violation
• Black holes in Einstein-aether and Horava-Lifshitz gravity
• Cuscuton and low energy limit of Horava-Lifshitz gravity
• Strong field effects on binary systems in Einstein-aether theory
• Slowly rotating black holes in Horava-Lifshitz gravity
• More on "Little Lambda" in Hořava-Lifshitz Gravity

Cited by in corpus (9)

• Stellar structure models in modified theories of gravity: lessons and challenges
• New binary pulsar constraints on Einstein-æther theory after GW170817
• The relation between general relativity and a class of Hořava gravity theories
• Canonical loop quantization of the lowest-order projectable Horava gravity
• Irreversible vierbein postulate: Emergence of spacetime from quantum phase transition
• I-Love-Q in Hořava-Lifshitz Gravity
• Well-posed evolution of field theories with anisotropic scaling: the Lifshitz scalar field in a black hole space-time
• Neutron Stars in Mimetic Gravity
• Degenerate Horava gravity