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arXiv · 2605.02008

Gravitational baryogenesis in scalar-nonmetricity $f(Q,ϕ)$ gravity

F. Mavoa·M. C. Sow·M. G. Ganiou·C. S. Touré·C. R. Tefo
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Abstract

In this work, we investigate gravitational baryogenesis in the framework of scalar-nonmetricity theories by considering two classes of modified gravity models, namely $f(Q,ϕ)=Q+ξQ ϕ^2$ and $f(Q,ϕ)=αQ^n + βϕQ$. These models extend standard $f(Q)$ gravity through the inclusion of nonminimal couplings between the scalar field and the nonmetricity scalar, leading to nontrivial modifications of the cosmological dynamics. We analyze the evolution of the baryon-to-entropy ratio in terms of the cosmic expansion parameter $γ$, assuming a power-law behavior of the scale factor. For the first model, we show that the baryon-to-entropy ratio decreases monotonically with increasing $γ$, reflecting the impact of the expansion rate on the efficiency of baryogenesis. The observed baryon asymmetry, of order $10^{-11}$ to $10^{-10}$, is successfully reproduced for $γ\approx 0.2$--$0.3$ without requiring fine-tuning of the model parameters. For the second model, we explore the parameter space of $α$ and $β$, and demonstrate that the correct order of magnitude of the baryon asymmetry can be achieved for physically reasonable values of the parameters. In particular, we find that the baryon-to-entropy ratio lies within observational bounds for $α\sim 10^{-3}$ to $10^{-2}$ and $β\sim 10^{-2}$ to $10^{-1}$, with specific combinations yielding excellent agreement with observations. Overall, our results show that scalar-nonmetricity gravity provides a viable and robust framework for explaining the origin of the baryon asymmetry of the Universe. The interplay between nonlinear geometric terms and scalar field couplings plays a crucial role in controlling the baryogenesis mechanism, opening new perspectives in the study of modified gravity and early Universe cosmology.

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F. Mavoa, M. C. Sow, M. G. Ganiou, C. S. Touré, C. R. Tefo. 2026-05-03. Gravitational baryogenesis in scalar-nonmetricity $f(Q,ϕ)$ gravity. https://arxiv.org/abs/2605.02008

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