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We propose a baryogenesis mechanism termed scalar-tensor baryogenesis, analogous to gravitational and spontaneous baryogenesis, driven by scalar fields arising from the scalar-tensor representation of modified gravity theories. This mechanism reproduces the original interaction term of gravitational baryogenesis and those commonly introduced in modified gravity contexts. We demonstrate the mechanism within $f(R,T)$ and $f(R)$ gravity frameworks, focusing on $f(R)$. We explore a quintessence potential given by $V(\phi) = \alpha \frac{\phi^{m+1}}{{m+1}}$ and a potential given $V(\phi) = \beta^{-\frac{1}{n-1}}(n-1)\left(\frac{\phi - 1}{n}\right)^{\frac{n}{n-1}}$ that corresponds in the geometric representation to models of the form $R + \beta R^n$. The model with $n=2$ presented the best behavior in generating an acceptable asymmetry during the radiation-dominated epoch. Inspired by this result, employing Planck data, we explored the Starobinsky inflation model obtaining successful baryogenesis during the inflationary epoch for both gravitational and scalar-tensor baryogenesis., Comment: 13 pages, 2 figures

This review delves into the pivotal primordial stage of the universe, a period that holds the key to understanding its current state. To fully grasp this epoch, it is essential to consider three fundamental domains of physics: gravity, particle physics, and thermodynamics. The thermal history of the universe recreates the extreme high-energy conditions that are critical for exploring the unification of the fundamental forces, making it a natural laboratory for high-energy physics. This thermal history also offers valuable insights into how the laws of thermodynamics have governed the evolution of the universe's constituents, shaping them into the forms we observe today. Focusing on the Standard Cosmological Model (SCM) and the Standard Model of Particles (SM), this paper provides an in-depth analysis of thermodynamics in the primordial universe. The structure of the study includes an introduction to the SCM and its strong ties to thermodynamic principles. It then explores equilibrium thermodynamics in the context of the expanding universe, followed by a detailed analysis of out-of-equilibrium phenomena that were pivotal in shaping key events during the early stages of the universe's evolution., Comment: 50 pages. Published version in Entropy of an invited contribution to the section "Astrophysics, Cosmology, and Black Holes"

We investigate the phenomenon of gravitational baryogenesis within the context of a specific modified theory of gravity, namely, energy-momentum squared gravity or $f(R, T_{\mu\nu}T^{\mu\nu})$ gravity. In this framework, the gravitational Lagrangian is formulated as a general function of the Ricci scalar $R$ and the self-contraction of the energy-momentum tensor, $\mathcal{T}^2 \equiv T_{\mu\nu}T^{\mu\nu}$. This approach extends the conventional paradigm of gravitational baryogenesis by introducing new dependencies that allow for a more comprehensive exploration of the baryon asymmetry problem. Our analysis aims to elucidate the role of these gravitational modifications in the generation of baryon asymmetry, a critical issue in cosmology that remains unresolved within the Standard Model of particle physics. By incorporating $\mathcal{T}^2$ into the gravitational action, we propose that these modifications can significantly influence the dynamics of the early universe, thereby altering the conditions under which baryogenesis occurs. This study not only provides a novel depiction of gravitational baryogenesis but also offers insights into how modified gravity theories can address the longstanding question of baryon asymmetry. The implications of our findings suggest that $f(R, T_{\mu\nu}T^{\mu\nu})$ gravity could play a crucial role in understanding the fundamental processes that led to the matter-antimatter imbalance observed in the universe today., Comment: 22 pages, 5 figures

Since the development of Brans-Dicke gravity, it has become well-known that a conformal transformation of the metric can reformulate this theory, transferring the coupling of the scalar field from the Ricci scalar to the matter sector. Specifically, in this new frame, known as the Einstein frame, Brans-Dicke gravity is reformulated as General Relativity supplemented by an additional scalar field. In 1959, Hans Adolf Buchdahl utilized an elegant technique to derive a set of solutions for the vacuum field equations within this gravitational framework. In this paper, we extend Buchdahl's method to incorporate the cosmological constant and to the scalar-tensor cases beyond the Brans-Dicke archetypal theory, thereby, with a conformal transformation of the metric, obtaining solutions for a version of Brans-Dicke theory that includes a quadratic potential. More specifically, we obtain synchronous solutions in the following contexts: in scalar-tensor gravity with massless scalar fields, Brans-Dicke theory with a quadratic potential, where we obtain specific synchronous metrics to the Schwarzschild-de Sitter metric, the Nariai solution, and a hyperbolically foliated solution., Comment: 16 pages. Published in Symmetry

In this review article, we revisit the topic of baryogenesis, which is the physical process that generated the observed baryon asymmetry during the first stages of the primordial Universe. A viable theoretical explanation to understand and investigate the mechanisms underlying baryogenesis must always ensure that the Sakharov criteria are fulfilled. These essentially state the following: (i) baryon number violation; (ii) the violation of both C (charge conjugation symmetry) and CP (the composition of parity and C); (iii) and the departure from equilibrium. Throughout the years, various mechanisms have been proposed to address this issue, and here we review two of the most important, namely, electroweak baryogenesis (EWB) and Grand Unification Theories (GUTs) baryogenesis. Furthermore, we briefly explore how a change in the theory of gravity affects the EWB and GUT baryogenesis by considering Scalar--Tensor Theories (STT), where the inclusion of a scalar field mediates the gravitational interaction, in addition to the metric tensor field. We consider specific STT toy models and show that a modification of the underlying gravitational theory implies a change in the time--temperature relation of the evolving cosmological model, thus altering the conditions that govern the interplay between the rates of the interactions generating baryon asymmetry, and the expansion rate of the Universe. Therefore, the equilibrium of the former does not exactly occur as in the general relativistic standard model, and there are consequences for the baryogenesis mechanisms that have been devised. This is representative of the type of modifications of the baryogenesis processes that are to be found when considering extended theories of gravity., Comment: 29 pages. Published version in Symmetry of an invited contribution to the Special Issue "Physics and Symmetry Section: Feature Papers 2023"