Causality Violation in Lovelock Theories

by Yotam Sherf

at Particles and Fields Seminar

Mon, 06 Nov 2017, 14:00
Physics building (#54) room 207

Abstract

Higher derivative gravity theories such as Lovelock theories generalize Einstein s general relativity GR Modifications to GR are expected when curvatures are near Planckian and appear in string theory or supergravity But can such theories describe gravity on length scales much larger than the cutoff length scale Here we find causality constraints on Lovelock theories that arise from the requirement that the equations of motion EOM of perturbations be hyperbolic We find a general expression for the effective metric in field space when Lovelock theories are perturbed around some background solution In particular we calculate explicitly the effective metric for a general Lovelock theory perturbed around cosmological Friedman Robertson Walker backgrounds and for some specific cases when perturbed around Schwarzschild like solutions For the EOM to be hyperbolic the effective metric needs to be Lorentzian We find that unlike for GR the effective metric is generically not Lorentzian when the Lovelock modifications are significant So we conclude that Lovelock theories can only be considered as perturbative extension of GR and not as truly modified theories of gravity We compare our results to those in the literature and find that they are consistent with the results of previous studies

Created on 31-10-2017 by Bar Lev, Yevgeny (ybarlev)
Updaded on 31-10-2017 by Bar Lev, Yevgeny (ybarlev)