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S. C. Ulhoa

Publications and source records attributed to S. C. Ulhoa.

At least 55 records · Page 3Linked to original sources
arXiv2019

The Work-Energy Relation for Particles on Geodesics in the pp-Wave Spacetimes

A non-linear gravitational wave imparts gravitational acceleration to all particles that are hit by the wave. We evaluate this acceleration for particles in the pp-wave space-times, and integrate it numerically along the geodesic trajectories of the particles during the passage of a burst of gravitational wave. The time dependence of the wave is given by a Gaussian, so that the particles are free before and after the passage of the wave. The gravitational acceleration is understood from the point of view of a flat space-time, which is the initial and final gravitational field configuration. The integral of the acceleration along the geodesics is the analogue of the Newtonian concept of work per unit mass. Surprisingly, it yields almost exactly the variation of the non-relativistic kinetic energy per unit mass of the free particle. Therefore, the work-energy relation $ΔK = ΔW$ of classical Newtonian physics also holds for a particle on geodesics in the pp-wave space-times, in a very good approximation, and explains why the final kinetic energy of the particle may be smaller or larger than the initial kinetic energy.

gr-qc↗
arXiv2019

On Lorentz violation in $e^{-}\!\!+\!e^{+}\!\rightarrow\!μ^{-}\!\!+\!μ^{+}$ scattering at finite temperature

Small violation of Lorentz and CPT symmetries may emerge in models unifying gravity with other forces of nature. An extension of the standard model with all possible terms that violate Lorentz and CPT symmetries are included. Here a CPT-even non-minimal coupling term is added to the covariant derivative. This leads to a new interaction term that breaks the Lorentz symmetry. Our main objective is to calculate the cross section for the $e^{-}\!\!+\!e^{+}\!\rightarrow\!μ^{-}\!\!+\!μ^{+}$ scattering in order to investigate any violation of Lorentz and/or CPT symmetry at finite temperature. Thermo Field Dynamics formalism is used to consider finite temperature effects.

hep-th↗
arXiv2018

On Quantization of a Slow Rotating Kerr Black Hole

In this article we calculate the total angular momentum for Kerr space-time for slow rotations. In order to analyze the role of such quantity we apply Weyl quantization method to obtain a quantum equation for the z-component of the angular momentum and for the squared angular momentum as well. We present an approximated solution by means the Adomian method. In such a method we find out a discrete angular momentum.

physics.gen-ph↗
arXiv2018

On Scalar Electromagnetism in Phase Space

In this paper the interaction of a scalar field and the electromagnetic field in phase space is analyzed. The scattering process is calculated up to first order in the Planck constant which is obtained by an expansion of the Moyal product in phase space. The transition amplitude is calculated in the same context.

hep-th↗
arXiv2018

Variations of the Energy of Free Particles in the pp-Wave Spacetimes

We consider the action of exact plane gravitational waves, or pp-waves, on free particles. The analysis is carried out by investigating the variations of the geodesic trajectories of the particles, before and after the passage of the wave. The initial velocities of the particles are non-vanishing. We evaluate numerically the Kinetic energy per unit mass of the free particles, and obtain interesting, quasi-periodic behaviour of the variations of the Kinetic energy with respect to the width $λ$ of the gaussian that represents the wave. The variation of the energy of the free particle is expected to be exactly minus the variation of the energy of the gravitational field, and therefore provides an estimation of the local variation of the gravitational energy. The investigation is carried out in the context of short bursts of gravitational waves, and of waves described by normalised gaussians, that yield impulsive waves in a certain limit.

gr-qc↗
arXiv2018

Kinetic Energy and Angular Momentum of Free Particles in the Gyratonic pp-Waves Space-times

Gyratonic pp-waves are exact solutions of Einstein's equations that represent non-linear gravitational waves endowed with angular momentum. We consider gyratonic pp-waves that travel in the $z$ direction and whose time dependence on the variable $u={1 \over \sqrt{2}}(z-t)$ is given by gaussians, so that the waves represent short bursts of gravitational radiation propagating in the $z$ direction. We evaluate numerically the geodesics and velocities of free particles in the space-time of these waves, and find that after the passage of the waves both the kinetic energy and the angular momentum per unit mass of the particles are changed. Therefore there is a transfer of energy and angular momentum between the gravitational field and the free particles, so that the final values of the energy and angular momentum of the free particles may be smaller or larger in magnitude than the initial values.

gr-qc↗
arXiv2018

Plane Gravitational Waves, the Kinetic Energy of Free Particles and the Memory Effect

It is shown that in the passage of a short burst of non-linear plane gravitational wave, the kinetic energy of free particles may either decrease or increase. The decreasing or increasing of the kinetic energy depends crucially on the initial conditions (position and velocity) of the free particle. Therefore a plane gravitational wave may extract energy from a physical system.

gr-qc↗
arXiv2018

On Quantum Cosmology in Teleparallel Gravity

A quantum cosmology in teleparallel gravity is presented in this article. Teleparallel gravity is used to perform such an analysis once in General Relativity (GR) the concept of gravitational energy is misleading preventing the establishment of a concise quantum cosmology. The Wheeler-DeWitt like equation is obtained using the Weyl quantization and the teleparallel expression of energy.

gr-qc↗
arXiv2018

Black Holes Thermodynamics in a new kind of Noncommutative Geometry

Motivated by the energy dependent metric in gravity's rainbow, we will propose a new kind of energy dependent noncommutative geometry. It will be demonstrated that like gravity's rainbow, this new noncommutative geometry is described by an energy dependent metric. We will analyse the effect of this noncommutative deformation on the Schwarzschild black holes and Kerr black holes. We will perform our analysis by relating the commutative and this new energy dependent noncommutative metrics using an energy dependent Moyal star product. We will also analyze the thermodynamics of these new noncommutative black hole solutions. We will explicitly derive expression for the corrected entropy and temperature for these black hole solutions. It will be demonstrated that for these deformed solutions black remnants cannot form. This is because these correction increase rather than reduce the temperature of the black holes.

gr-qc↗
arXiv2017

On Gravitational Energy in Conformal Teleparallel Gravity

The paper deals with the definition of gravitational energy in conformal teleparallel gravity. The total energy is defined by means of the field equations which allow a local conservation law. Then such an expression is analyzed for a homogeneous and isotropic Universe. This model is implemented by the Friedmann-Robertson-Walker (FRW) line element. The energy of the universe in the absence of matter is identified with the dark energy, however it can be expanded for curved models defining such an energy as the difference between the total energy and the energy of the perfect fluid which is the matter field in the FRW model.

gr-qc↗
arXiv2017

On Fermion-Graviton Scattering at Finite Temperature

The early universe is dominated by phenomena at high temperatures. The thermal effects decrease during evolution of the universe. However there are some phenomena, such as processes inside stars and black holes, where the role of the temperature is important. Study of processes involving gravitons at finite temperature is a viable means to understand gravitational processes in the universe. Using the Thermo Field Dynamics formalism transition amplitudes involving gravitons and fermions at finite temperature are calculated. In this approach our results consist of two parts: one corresponding to the zero temperature part and the other corresponding to a temperature dependent part.

gr-qc↗
arXiv2017

Non-relativistic Casimir effect at finite temperature

The Galilean covariance, formulated in 5-dimensions space, describes the non-relativistic physics in a way similar to quantum field theory. Using a non-relativistic approach the Stefan-Boltzmann law and the Casimir effect at finite temperature for a particle with spin zero and $1/2$ are calculated. The Thermo Field Dynamics is used to calculate the temperature effect.

hep-th↗
arXiv2016

Approximative Wigner function for the Helium atom and dissipation

The Schrödinger equation in phase space is used to calculate the Wigner function for the Helium atom in the approximation of a system of two oscillators. Dissipation effect is analysed and the non-classicality of the state is studied by the non-classicality indicator of the Wigner function, which is calculated as a function of the dissipation parameter.

quant-ph↗
arXiv2016

Scattering of Fermions by Gravitons

The interaction between gravitons and fermions is investigated in the teleparallel gravity. The scattering of fermions and gravitons in the weak field approximation is analyzed. The transition amplitudes of M$\varnothing$ller, Compton and new gravitational scattering are calculated.

gr-qc↗
arXiv2016

On FRW Model in Conformal Teleparallel Gravity

In this paper we use the conformal teleparallel gravity to study an isotropic and homogeneous Universe which is settled by the FRW metric. We solve the field equations and we obtain the behavior of some cosmological parameters such as scale factor, deceleration parameter and the energy density of the perfect fluid which is the matter field of our model. The field equations, that we called modified Friedmann equations, allow us to define a dark fluid, with dark energy density and dark pressure, responsible for the acceleration in the Universe.

gr-qc↗
arXiv2016

Hénon-Heiles Interaction for Hydrogen Atom in Phase Space

Using elements of symmetry, as gauge invariance, several aspects of a Schrödinger equation represented in phase-space are introduced and analyzed under physical basis. The Hydrogen atom is explored in the same context. Then we add a Hénon-Heiles potential to the Hydrogen atom in order to explore chaotic features.

quant-ph↗