4 research outputs found
Comment on `Strong coupling in extended Horava-Lifshitz gravity'
We show that, contrary to the claim made in arXiv:0911.1299, the extended
Horava gravity model proposed in arXiv:0909.3525 does not suffer from a strong
coupling problem. By studying the observational constraints on the model we
determine the bounds on the scale of the ultraviolet modification for which the
proposal yields a phenomenologically viable, renormalizable and weakly coupled
model of quantum gravity.Comment: A footnote discussing the absence of fine-tuning is adde
Perturbative instabilities in Horava gravity
We investigate the scalar and tensor perturbations in Horava gravity, with
and without detailed balance, around a flat background. Once both types of
perturbations are taken into account, it is revealed that the theory is plagued
by ghost-like scalar instabilities in the range of parameters which would
render it power-counting renormalizable, that cannot be overcome by simple
tricks such as analytic continuation. Implementing a consistent flow between
the UV and IR limits seems thus more challenging than initially presumed,
regardless of whether the theory approaches General Relativity at low energies
or not. Even in the phenomenologically viable parameter space, the tensor
sector leads to additional potential problems, such as fine-tunings and
super-luminal propagation.Comment: 21 pages, version published at Class. Quant. Gra
Black Holes in Ho\v{r}ava Gravity with Higher Derivative Magnetic Terms
We consider Horava gravity coupled to Maxwell and higher derivative magnetic
terms. We construct static spherically symmetric black hole solutions in the
low-energy approximation. We calculate the horizon locations and temperatures
in the near-extremal limit, for asymptotically flat and (anti-)de Sitter
spaces. We also construct a detailed balanced version of the theory, for which
we find projectable and non-projectable, non-perturbative solutions.Comment: 17 pages. v2: Up to date with published version; some minor remarks
and more reference
Tests of Lorentz invariance: a 2013 update
We present an updated review of Lorentz invariance tests in effective field theories (EFTs) in the matter as well as in the gravity sector. After a general discussion of the role of Lorentz invariance and a derivation of its transformations along the so-called von Ignatovski theorem, we present the dynamical frameworks developed within local EFT and the available constraints on the parameters governing the Lorentz breaking effects. In the end, we discuss two specific examples: the OPERA 'affaire' and the case of Ho\u159ava- Lifshitz gravity. The first case will serve as an example, and a caveat, of the practical application of the general techniques developed for constraining Lorentz invariance violation to a direct observation potentially showing these effects. The second case will show how the application of the same techniques to a specific quantum gravity scenario has far-reaching implications not foreseeable in a purely phenomenological EFT approach