Big Bang Nucleosynthesis constraints on higher-order modified gravities

Abstract: We use Big Bang Nucleosynthesis (BBN) data in order to impose constraints on higher-order modified gravity, and in particular on: (i) $f(G)$ Gauss-Bonnet gravity, and $f(P)$ cubic gravities, arising respectively through the use of the quadratic-curvature Gauss-Bonnet $G$ term, and the cubic-curvature combination, (ii) string-inspired quadratic Gauss-Bonnet gravity coupled to the dilaton field, (iii) models with string-inspired quartic curvature corrections, and (iv) running vacuum models. We perform a detailed investigation of the BBN epoch and we calculate the deviations of the freeze-out temperature $T_f$ in comparison to $\Lambda$CDM paradigm. We then use the observational bound on $ \left|\frac{\delta {T}_f}{{T}_f}\right|$ in order to extract constraints on the involved parameters of various models. We find that all models can satisfy the BBN constraints and thus they constitute viable cosmological scenarios, since they can additionally account for the dark energy sector and the late-time acceleration, in a quantitative manner, without spoiling the formation of light elements during the BBN epoch. Nevertheless, the obtained constraints on the relevant model parameters are quite strong.