Constraints on bimetric gravity from Big Bang nucleosynthesis

Understand

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.