Testing Hořava-Lifshitz gravity using thin accretion disk properties

Abstract

Recently, a renormalizable gravity theory with higher spatial derivatives in four dimensions was proposed by Ho\ifmmode \check{r}\else \v{r}\fi{}ava. The theory reduces to Einstein gravity with a nonvanishing cosmological constant in IR, but it has improved UV behaviors. The spherically symmetric black hole solutions for an arbitrary cosmological constant, which represent the generalization of the standard Schwarzschild--(anti) de Sitter solution, have also been obtained for the Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz theory. The exact asymptotically flat Schwarzschild-type solution of the gravitational field equations in Ho\ifmmode \check{r}\else \v{r}\fi{}ava gravity contains a quadratic increasing term, as well as the square root of a fourth order polynomial in the radial coordinate, and it depends on one arbitrary integration constant. The IR-modified Ho\ifmmode \check{r}\else \v{r}\fi{}ava gravity seems to be consistent with the current observational data, but in order to test its viability more observational constraints are necessary. In the present paper we consider the possibility of observationally testing Ho\ifmmode \check{r}\else \v{r}\fi{}ava gravity by using the accretion disk properties around black holes. The energy flux, the temperature distribution, the emission spectrum, as well as the energy conversion efficiency are obtained, and compared to the standard general relativistic case. Particular signatures can appear in the electromagnetic spectrum, thus leading to the possibility of directly testing Ho\ifmmode \check{r}\else \v{r}\fi{}ava gravity models by using astrophysical observations of the emission spectra from accretion disks.