arXiv subjects

Laysa G. Martins

Publications and source records attributed to Laysa G. Martins.

4 recordsLinked to original sources

arXiv2025

Thermodynamics and Bouncing Cosmology in Rastall-like Gravity

In this study, we explore the thermodynamic aspects of a modified version of Rastall's gravity theory and its implications for cosmological scenarios. We analyze the role of non-conserved energy-momentum tensor equations and investigate their influence on particle production within an irreversible thermodynamic framework. By introducing a novel Lagrangian, we derive modified field equations and establish their relationship with matter production, both with and without entropy generation. Our analysis focuses on ideal fluid models and extends to spatially flat LFRW cosmologies, providing key equations that govern energy density, pressure, and curvature dynamics. Furthermore, we propose a bouncing cosmological model, in which the universe undergoes cycles of contraction and expansion, avoiding the singularity associated with the Big Bang. Our results indicate that this bouncing scenario is feasible within the Rastall-like gravity framework, supported by particle production processes and stability conditions. The violation of energy conditions near the bounce point further confirms the consistency of this alternative cosmological model. The present work is focused on the theoretical foundations and internal consistency of the model; possible observational implications will be addressed in future investigations. We conclude that the proposed theory offers a coherent phenomenological approach to matter production and provides new insights into non-standard cosmological evolution.

gr-qc↗

arXiv2020

Quantization of the interior of the black hole

In this work we study the Schwarzschild metric in the context of canonical quantum gravity inside the horizon, close of horizon and near the black hole singularity. Using this standard quantization procedure, we show that the horizon is quantized and the black hole singularity disappears. For the first case, quantization of the Schwarzschild radius was obtained in terms of the Planck length $l_{Pl}$, a positive integer $n$ and the ordering factor of the operator $p$. From the quantization of the Schwarzschild radius it was possible to determine the area of the black hole event horizon, its mass and the quantum energy of the Hawking radiation as well as its frequency. For the solution close to the interior black hole singularity, the wave function was determined and applied the DeBroglie-Bohm interpretation. The Bohm's trajectory was found near to the singularity. It which describes how the spacetime evolves over time and depends on the ordering factor of the operator $p$. Thus, for the case where $|1-p|\neq0,3$, the Bohm's trajectory is finite and regular, that is, the singularity is removed. For the case where $|1-p|=3$, the Bohm's trajectory assumes an exponential behavior, never going to zero, avoiding the singularity.That result allows that spacetime be extended beyond the classical singularity.

gr-qc↗

arXiv2015

Quantum Hořava-Lifshitz cosmology and the quantum nature of coupling corrections of HL gravity

In this work were studied quantum models of a Friedmann-Robertson-Walker (FRW) cosmology in the framework of the gravity's theory proposed by Hořava, the so-called Hořava-Lifshitz theory of the gravity. It was used the Hořava theory for the projectable Hořava-Lifshitz (HL) gravity without the detailed balance condition. Following the quantization of the model in the context of Wheeler-DeWitt approach and taking in account the ordering factor for operators were found the cosmological wave function. Solutions were studied and the results were discussed for some particular cases close of initial singularity. The resulting wave functions were used to investigate the possibility of to avoid the classical singularities due to quantum effects and for analyzing the entanglement entropy. In the ultraviolet phase were found the existence of cosmological wave function with a relation between the ordering factor and coupling constants showing their quantum nature, then it was possible to provide an explicit evolution of the cosmological entanglement entropy in this stage. The interpretation of Bohm-De Broglie was used to discussion of the solutions.

gr-qc↗

arXiv2013

The dynamics of a rotating ellipsoid

An interesting physical phenomenon, which contradicts our common sense, is concerned with the dynamics of motion of a spinning ellipsoid in a non smooth surface. A hard-boiled egg spinning on a table with a rough surface is an example. In this article, we present a theoretical explanation, of the dynamics of motion of this ellipsoid, that describes the axis raising phenomenon, from the horizontal to the vertical. The equations of motion were obtained with Lagrangian formalism.

physics.ed-ph↗