### Horava Gravity in the Effective Field Theory formalism: from cosmology to observational constraints

(0 votes over all institutions)

We consider Horava gravity within the framework of the EFT of dark energy and modified gravity. We work out a complete mapping of the theory into the EFT language for an action including all the operators which are relevant for linear perturbations with up to sixth order spatial derivatives. We then employ an updated version of the EFTCAMB/EFTCosmoMC package to study the cosmology of the low-energy limit of Horava gravity and place constraints on its parameters using several cosmological data sets. In particular we consider two cases: the first in which the three parameters of the low-energy theory are all varied and a second case that is tuned to evade PPN constraints, reducing the number of free parameters to two. We employ data sets which include the CMB TT and lensing power spectra by Planck 2013, WMAP low-l polarization spectra, the WiggleZ galaxy power spectrum, the local Hubble measurements, Supernovae data from SNLS, SDSS and HST and the BAO measurements from BOSS, SDSS and 6dFGS. For both cases we estimate the deviation of the cosmological gravitational constant from the local Newtonian one, getting improved upper bounds with respect to the previous ones from BBN data. At the level of the background, we find a relevant rescaling of the Hubble rate at all epoch, which has a strong impact on the cosmological observables; at the level of perturbations, we discuss all the relevant effects that the modifications of gravity induce, ranging from modifications of the late time ISW effect, the growth of matter perturbations, gravitational lensing and differences in the B-modes of the CMB. In general the quasi-static approximation is not safe to describe the evolution of perturbations in Horava gravity. Overall we find that the effects of the modifications induced by the low-energy Horava gravity action are quite dramatic and current data place tight bounds on the theory parameters.