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arXiv · 1503.07521

Bimetric gravity is cosmologically viable

Yashar Akrami·S. F. Hassan·Frank Könnig·Angnis Schmidt-May·Adam R. Solomon
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Abstract

Bimetric theory describes gravitational interactions in the presence of an extra spin-2 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 spin-2 interaction scale. This provides a late-time expansion history which is extremely close to $Λ$CDM, but with a technically-natural 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 big-bang nucleosynthesis. We further show that in this limit the helicity-0 mode is no longer strongly-coupled at low energy scales.

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Yashar Akrami, S. F. Hassan, Frank Könnig, Angnis Schmidt-May, Adam R. Solomon. 2015-07-04. Bimetric gravity is cosmologically viable. https://doi.org/10.1016/j.physletb.2015.06.062

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