Perturbations in massive gravity cosmology
Abstract
We study cosmological perturbations for a ghost free massive gravity theory formulated with a dynamical extra metric that is needed to massive deform GR. In this formulation FRW background solutions fall in two branches. In the dynamics of perturbations around the first branch solutions, no extra degree of freedom with respect to GR is present at linearized level, likewise what is found in the Stuckelberg formulation of massive gravity where the extra metric is flat and non dynamical. In the first branch, perturbations are probably strongly coupled. On the contrary, for perturbations around the second branch solutions all expected degrees of freedom propagate. While tensor and vector perturbations of the physical metric that couples with matter follow closely the ones of GR, scalars develop an exponential Jeanslike instability on subhorizon scales. On the other hand, around a de Sitter background there is no instability. We argue that one could get rid of the instabilities by introducing a mirror dark matter sector minimally coupled to only the second metric.
 Publication:

Journal of High Energy Physics
 Pub Date:
 June 2012
 DOI:
 10.1007/JHEP06(2012)085
 arXiv:
 arXiv:1202.1986
 Bibcode:
 2012JHEP...06..085C
 Keywords:

 Cosmology of Theories beyond the SM;
 Classical Theories of Gravity;
 High Energy Physics  Theory;
 Astrophysics  Cosmology and Extragalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 18 pages, 1 figure. Final version published in JHEP. arXiv admin note: substantial text overlap with arXiv:1111.1983