New models and big bang nucleosynthesis constraints in f(Q) gravity

Abstract The f (Q) theories of modified gravity arise from the consideration of non-metricity as the basic geometric quantity, and have been proven to be very efficient in describing the late-time Universe. We use the Big Bang Nucleosynthesis (BBN) formalism and observations in order to extract constraints on various classes of f (Q) models. In particular, we calculate the deviations that f (Q) terms bring on the freeze-out temperature Tf T f in comparison to that of the standard Λ CDM evolution, and then we impose the observational bound on | Tf{Tf}| δ T f T f to extract constraints on the involved parameters of the considered models. Concerning the polynomial model, we show that the exponent parameter should be negative, while for the power-exponential model and the new hyperbolic tangent-power model we find that they pass the BBN constraints trivially. Finally, we examine two DGP-like f (Q) models, and we extract the bounds on their model parameters. Since many gravitational modifications, although able to describe the late-time evolution of the Universe, produce too-much modification at early times and thus fall to pass the BBN confrontation, the fact that f (Q) gravity can safely pass the BBN constraints is an important advantage of this modified gravity class.