arXiv subjects

Omar Gallegos

Publications and source records attributed to Omar Gallegos.

5 recordsLinked to original sources

arXiv2026

Entropy in Loop Quantum Cosmology

The Generalized First Law (GFL) and the Generalized Second Law (GSL) of thermodynamics are studied for cosmological scenarios with spatial curvature through an apparent horizon. We focus on effective and alternative cosmic systems motivated by quantum cosmological models, where the entropy is considered a function of the apparent area, transforming the effective cosmological model into the standard form in cosmology. The general conditions for the validity of the GSL are analyzed for entropy as a general function of area and logarithmic corrections to the usual Black Hole entropy. The Weak Energy Condition (WEC) and the Strong Energy Condition (SEC) are implemented for the matter entropy part. In particular, we study the GFL and the regions where the GSL is valid for effective Loop Quantum Cosmology (LQC) models with spatial curvature $k=0,\pm 1$, taking every possible value of the logarithmic contributing factor for the entropy analysis. In addition, in order to solve some violations of the GSL, we explore the possibility of admitting negative absolute temperatures (NAT) in our system, where the validity conditions for an extended generalized second law (EGSL) are studied, and the time arrow from the second law is discussed for the LQC models.

gr-qc↗

arXiv2026

An Extended Second Law of Thermodynamics

The second law of thermodynamics constitutes a fundamental principle of physics, precluding the existence of perpetual motion machines and providing a natural definition of the arrow of time. Its scope extends across virtually all areas of physical theory. Nonetheless, certain systems are known to admit negative absolute temperatures under well-defined conditions, a phenomenon that has been experimentally observed. In this work, we formulate an extended version of the first and second laws, which recovers the conventional statement for positive temperatures and extends its applicability to the negative-temperature domain. Illustrative examples are discussed in the contexts of quantum cosmology and Onsager's vortices.

gr-qc↗

arXiv2025

Unitary evolution and cosmic acceleration in Loop Quantum Cosmology

Loop quantum cosmology was shown to interpolate between de Sitter and FLRW Universe phases through a bounce by including Euclidean and Lorentzian terms of the Hamiltonian constraint with weight one -that corresponding to classical General Relativity. Unitary evolution required self-adjoint extensions of the constraint and a Planckian cosmological constant was obtained. Independent work took a positive weight to get a cosmological constant with the observed value, without considering unitarity. In this work we address the unitary evolution of the model for arbitrary weight. For non positive weight parameter unitary holds but for positive values self-adjoint extensions are required. To encompass observations the extensions here provided are mandatory. These are implemented in a propagator. Finally, we discuss our results and perspectives.

gr-qc↗

arXiv2022

Hydrodynamic representation and Energy Balance for Dirac and Weyl fermions in curved space-times

Using a generalized Madelung transformation, we derive the hydrodynamic representation of the Dirac equation in arbitrary curved space-times coupled to an electromagnetic field. We obtain Dirac-Euler equations for fermions involving a continuity equation and a first integral of the Bernoulli equation. Comparing between the Dirac and Klein-Gordon equations we obtain the balance equation for fermion particles. We also use the correspondence between fermions and bosons to derive the hydrodynamic representation of the Weyl equation which is a chiral form of the Dirac equation.

gr-qc↗

arXiv2021

Weak gravitational quantum effects in boson particles

We rewrite the Klein-Gordon (KG) equation in an arbitrary space-time transforming it into a generalized Schrödinger equation. Then we take the weak field limit and show that this equation has some differences with the traditional Schrödinger equation plus a gravitational field. Thus, this procedure shows that the Schrödinger equation derived in a covariant manner is different from the traditional one. With this new Schrödinger equation, we study the KG equation in a Newtonian space-time to describe the behavior of a scalar particle in an inertial system. We give some examples where it is possible to study the energy levels, effective potential and the wave function of the systems, these results contain the gravitational effects due to the curvature of space-time. We show that it is possible to verify experimentally these effects in a laboratory using non-inertial reference frames.

gr-qc↗