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

TL;DR

This paper maps Horava gravity into the effective field theory framework, analyzes its cosmological implications using updated data sets, and places tight observational constraints on its parameters, revealing significant effects on cosmological observables.

Contribution

It provides a comprehensive mapping of Horava gravity into EFT, applies an advanced numerical tool to cosmology, and derives new observational bounds on the theory's parameters.

Findings

Tight upper bounds on deviations of gravitational constant from local measurements.

Significant impact on the Hubble rate and cosmological observables.

Quasi-static approximation is generally invalid for perturbation evolution.

Abstract

We consider Horava gravity within the framework of the effective field theory (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 use cosmic microwave background (CMB) temperature-temperature and lensing power spectra by Planck 2013, WMAP low-l polarization spectra, WiggleZ galaxy power spectrum, local Hubble measurements, Supernovae data from SNLS, SDSS and HST and the baryon acoustic oscillations measurements from BOSS, SDSS and 6dFGS. We get improved upper bounds, with respect to those from Big Bang Nucleosynthesis, on the deviation of the cosmological gravitational constant from the local Newtonian one. At the level of the background phenomenology, 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 in details all the relevant effects on the observables and find that in general the quasi-static approximation is not safe to describe the evolution of perturbations. 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.