23-27 September 2019
Mainz Institute for Theoretical Physics, Johannes Gutenberg University
Europe/Berlin timezone

Modified gravity models: renormalization and cosmological implications

26 Sep 2019, 11:15
50m
02.430 (Mainz Institute for Theoretical Physics, Johannes Gutenberg University)

02.430

Mainz Institute for Theoretical Physics, Johannes Gutenberg University

Staudingerweg 9 / 2nd floor, 55128 Mainz
Regular Seminar

Speaker

Andrei Barvinsky

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.

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