Neutron star sensitivities in Hov{r}ava gravity after GW170817. (arXiv:1907.05958v1 [gr-qc])

<a href="http://arxiv.org/find/gr-qc/1/au:+Barausse_E/0/1/0/all/0/1">Enrico Barausse</a>

Hov{r}ava 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 bounded by solar

system and gravitational wave propagation experiments, but $lambda$ remains

relatively unconstrained ($0leqlambdalesssim 0.01-0.1$). 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, and find that they vanish

identically, like in the black hole case, for $alpha=beta=0$ and generic

$lambdaneq0$. 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 $lambda$.

Hov{r}ava 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 bounded by solar

system and gravitational wave propagation experiments, but $lambda$ remains

relatively unconstrained ($0leqlambdalesssim 0.01-0.1$). 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, and find that they vanish

identically, like in the black hole case, for $alpha=beta=0$ and generic

$lambdaneq0$. 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 $lambda$.

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