arXiv subjects

F. Mavoa

Publications and source records attributed to F. Mavoa.

3 recordsLinked to original sources

arXiv2026

Periodic cosmic evolution in Hybrid and Logarithmic Teleparallel Gravity

In this work, we investigate a cosmological model within modified teleparallel gravity using two functional forms of $f(T)$: a hybrid model $f(T)=e^{\gamma T}T^{\sigma}$ and a logarithmic model, in the context of a periodic cosmic evolution driven by an oscillating deceleration parameter $q(t)=m\cos(kt)-1$. This approach describes a cyclic Universe with successive transitions between decelerating and accelerating phases. By constraining the model with observational values $m \simeq 0.48$ and $H_0 = 69.2\,\text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1}$, we recover the present accelerated expansion with $q_0 \approx -0.52$, while larger values $m \geq 1$ lead to strongly oscillatory regimes including super-acceleration. For the hybrid model ($\gamma = 0.1$, $\sigma = -0.5$), the energy density remains positive, while the pressure oscillates. The equation of state evolves dynamically, crossing both quintessence and phantom regimes. In contrast, the logarithmic model stabilizes the dynamics, regularizes divergences, and yields smoother evolution, with the equation of state mainly remaining in the quintessence regime. The analysis of energy conditions shows that the violation of the SEC supports accelerated expansion, while the partial validity of NEC and DEC ensures physical consistency. Overall, this framework provides a flexible alternative to the standard $\Lambda$CDM model, allowing a unified description of different phases of cosmic expansion.

gr-qc↗

arXiv2026

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

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.

gr-qc↗

arXiv2026

Inflationary Scenarios in $f(Q,\phi)$ Gravity with Scalar Field Coupling

In this work, we investigated several inflationary scenarios within the framework of modified $f(Q,\phi)$ gravity with a nonminimal coupling between the scalar field and the nonmetricity scalar. We focused on the impact of the coupling parameter $\xi$ on the inflationary observables, namely the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$. In the case of De Sitter inflation, we showed that the model can reproduce observationally viable predictions only within a restricted range of the coupling parameter. Specifically, we found that $n_s$ increases with $\xi$, while $r$ decreases, leading to a narrow allowed region $10^{-3} \lesssim \xi \lesssim 10^{-2}$ compatible with Planck data. Outside this range, the model either predicts excessively large tensor modes or an unphysical blue-tilted spectrum. We also derived theoretical constraints on $\xi$ from the consistency of the model, leading to an upper bound $\xi < \frac{\kappa}{2p}$. For $\kappa = 1$ and $p = 60$, this implies $\xi < 0.00833$, with a preferred region around $\xi \sim \mathcal{O}(10^{-3})$. Furthermore, we analyzed the Cosh-type inflationary model and showed that it provides a robust and consistent description of inflation. In this case, the tensor-to-scalar ratio decreases while the scalar spectral index increases with the number of e-folds $N$. For $N = 60$, the model predicts $n_s \approx 0.965 - 0.967, \qquad r \approx 0.017 - 0.018$, in excellent agreement with current observational constraints. Overall, our results highlight the crucial role of the nonminimal coupling in shaping the inflationary dynamics and ensuring compatibility with cosmological observations.

gr-qc↗