Big Bang Nucleosynthesis constraints on $f(T,T_G)$ gravity

TL;DR

This paper investigates how $f(T,T_G)$ gravity models affect Big Bang Nucleosynthesis, deriving constraints on model parameters by comparing deviations in the freeze-out temperature to observational bounds.

Contribution

It introduces constraints on $f(T,T_G)$ gravity models based on BBN requirements, analyzing specific models and their parameter bounds to ensure consistency with observed nucleosynthesis.

Findings

Most models require parameters close to General Relativity values.

Power-law model's exponent n must be less than approximately 0.5.

Logarithmic model easily satisfies BBN constraints across a wide parameter space.

Abstract

We confront $f(T,T_G)$ gravity, with Big Bang Nucleosynthesis (BBN) requirements. The former is obtained using both the torsion scalar, as well as the teleparallel equivalent of the Gauss-Bonnet term, in the Lagrangian, resulting to modified Friedmann equations in which the extra torsional terms constitute an effective dark energy sector. We calculate the deviations of the freeze-out temperature $T_f$, caused by the extra torsion terms in comparison to $\Lambda$CDM paradigm. Then we impose five specific $f(T,T_G)$ models and we extract the constraints on the model parameters in order for the ratio $|\Delta T_f/ T_f|$ to satisfy the observational BBN bound. As we find, in most of the models the involved parameters are bounded in a narrow window around their General Relativity values as expected, as in the power-law model where the exponent $n$ needs to be $n\lesssim 0.5$. Nevertheless the logarithmic model can easily satisfy the BBN constraints for large regions of the model parameters. This feature should be taken into account in future model building.