Big Bang Nucleosynthesis constraints on higher-order modified gravities
  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.
