Big Bang Nucleosynthesis constraints on the Energy-Momentum Squared Gravity: The 𝕋^2 model

A scale-independent energy-momentum squared gravity (EMSG) allows different gravitational couplings for different types of sources and has been proven to have interesting implications in cosmology. In this paper, the Big Bang Nucleosynthesis (BBN) formalism and the latest observational constraints are being used in order to extract constraints on this class of modified gravity models. The model has been constrained using the light element reaction rates. Using the tight constraint from BBN on the correction term in the Friedman equation due to EMSG, we find a significant deviation in the matter power spectrum of the cosmic microwave background (CMB) even for a very small allowed value of the modification parameter, thus pointing out the sensitivity of the matter power spectrum at the small scales.