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

Abstract

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 $$T_f$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>f</mml:mi> </mml:msub> </mml:math> in comparison to that of the standard $$\Lambda $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math> CDM evolution, and then we impose the observational bound on $$ \left| \frac{\delta {T}_f}{{T}_f}\right| $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mfrac> <mml:mrow> <mml:mi>δ</mml:mi> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>f</mml:mi> </mml:msub> </mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>f</mml:mi> </mml:msub> </mml:mfrac> </mml:mfenced> </mml:math> 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.

Topics & Concepts