Speaker
Description
We consider two classes of modified gravity models characterized by violation of Lorentz symmetry. One class of models is motivated by the search for a local renormalizable quantum gravity perturbatively consistent in UV domain. It consists of projectable Horava-Lifshitz models for which we show perturbative renormalizability in arbitrary dimension and prove their asymptotic freedom in the toy-model case of (2+1)-dimensional spacetime. Renormalization group flow is also built in (3+1)-dimensional Horava gravity for two of its coupling constants, indicating a potential domain of its asymptotic freedom for all seven couplings of this theory. Another class of models is motivated by the search for a possible mechanism of inflation and cosmological acceleration. This is the generalized unimodular gravity sharing in common with Horava models a peculiar kinematical restriction on the ADM lapse function, which manifests itself in the form of a special type of dark perfect fluid composed entirely from the metric sector of the theory and having a time dependent equation of state. Extra degree of freedom in this model -- scalar graviton -- has a nontrivial domain of unitarity and can drive inflationary scenario with scalar and tensor power spectra fitting observations. Quite remarkably, this model satisfies naturalness criterion -- O(1) magnitude of all theory parameters. This is because a typically accepted exponentially big e-folding factor, $e^{N}$, $N\sim 60$, for this model enters a special expression for tensor to scalar ratio $r\sim e^{-N(1-n_s)}\simeq 10^{-3}$, $n_s\simeq 0.96$ being the scalar red tilt, and easily satisfies known phenomenological bounds.
