Constraints on bimetric gravity from Big Bang nucleosynthesis

TL;DR

This paper uses Big Bang nucleosynthesis data to place new constraints on bimetric gravity, an extension of general relativity with both massless and massive gravitons, improving existing bounds.

Contribution

It provides novel constraints on bimetric gravity parameters from primordial element abundances, complementing other observational methods.

Findings

Mixing angle between gravitons must be less than 18 degrees.

Constraints are tighter for graviton mass above 10^{-16} eV/c^2.

Improves previous bounds by a factor of two.

Abstract

Bimetric gravity is a ghost-free and observationally viable extension of general relativity, exhibiting both a massless and a massive graviton. The observed abundances of light elements can be used to constrain the expansion history of the Universe at the period of Big Bang nucleosynthesis. Applied to bimetric gravity, we readily obtain constraints on the theory parameters which are complementary to other observational probes. For example, the mixing angle between the two gravitons must satisfy $\theta \lesssim 18^\circ$ in the graviton mass range $m_\mathrm{FP} \gtrsim 10^{-16} \, \mathrm{eV}/c^2$, representing a factor of two improvement compared with other cosmological probes.