Bimetric gravity is cosmologically viable
Abstract
Bimetric theory describes gravitational interactions in the presence of an extra spin2 field. Previous work has suggested that its cosmological solutions are generically plagued by instabilities. We show that by taking the Planck mass for the second metric, M_{f}, to be small, these instabilities can be pushed back to unobservably early times. In this limit, the theory approaches general relativity with an effective cosmological constant which is, remarkably, determined by the spin2 interaction scale. This provides a latetime expansion history which is extremely close to ΛCDM, but with a technicallynatural value for the cosmological constant. We find M_{f} should be no larger than the electroweak scale in order for cosmological perturbations to be stable by bigbang nucleosynthesis. We further show that in this limit the helicity0 mode is no longer stronglycoupled at low energy scales.
 Publication:

Physics Letters B
 Pub Date:
 September 2015
 DOI:
 10.1016/j.physletb.2015.06.062
 arXiv:
 arXiv:1503.07521
 Bibcode:
 2015PhLB..748...37A
 Keywords:

 Modified gravity;
 Massive gravity;
 Background cosmology;
 Cosmic acceleration;
 Dark energy;
 Bimetric gravity;
 Bigravity;
 General Relativity and Quantum Cosmology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 High Energy Physics  Theory
 EPrint:
 8+2 pages, 2 tables. Version published in PLB. Minor typo corrections from v3