كيف تفسر الجاذبية المعدلة عالمنا سريع

الملخص الأصلي

كما كتبه المؤلفون، بالإنجليزية arXiv:2605.02008

In this work, we investigate gravitational baryogenesis in the framework of scalar-nonmetricity theories by considering two classes of modified gravity models, namely $$f(Q,\phi)=Q+\xi Q \phi^2$$ and $$f(Q,\phi)=\alpha Q^n + \beta \phi Q$$. 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 $$\gamma$$, 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 $$\gamma$$, 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 $$\gamma \approx 0.2$$--$$0.3$$ without requiring fine-tuning of the model parameters. For the second model, we explore the parameter space of $$\alpha$$ and $$\beta$$, 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 $$\alpha \sim 10^{-3}$$ to $$10^{-2}$$ and $$\beta \sim 10^{-2}$$ 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.