arXiv subjects

João P. B. Brito

Publications and source records attributed to João P. B. Brito.

7 recordsLinked to original sources

arXiv2026

Interaction of the gravitational Hawking radiation and a static point mass

We study the interaction of a stress-energy tensor describing a static point mass supported by a string outside a Schwarzschild black hole with the gravitons of the Hawking radiation. We derive a closed-form analytic expression for the total response rate of this stress-energy tensor to the thermal gravitons in the Unruh state, which models the quantum state in the spacetime of a spherically symmetric black hole formed by gravitational collapse. This response rate is finite in contrast with the infrared divergent response rate for a static point mass supported by a string in Rindler spacetime, i.e., a point mass accelerated uniformly by a string in Minkowski spacetime. By comparing the response rate near the black hole horizon with that in Rindler spacetime, we show that the size of the black hole acts as a natural infrared cutoff. We also find that the response rate of this stress-energy tensor to the thermal gravitons incoming from past null infinity in the Hartle-Hawking state vanishes. As a result, the total response rate of a static point mass (supported by a string) in the Unruh and Hartle-Hawking states for gravitons are identical. This is also the case for a static charge interacting with the electromagnetic field but not for a static source for a massless scalar field.

gr-qc↗

arXiv2025

Multipole decomposition of the gravitational field of a point mass at the black hole horizon

The portion of the gravitational energy absorbed by the black hole due to the radial infall of a point mass is known to diverge at leading order in perturbation theory. This divergence is an artifact of the point-particle model, where the contribution of each multipole to the total absorbed energy is observed to be roughly constant. We show explicitly that this divergent energy arises from the infinite energy present in the singular static field arbitrarily close to the point mass, which also flows into the black hole when the particle trajectory crosses the horizon. We perform a multipole decomposition of the linearized gravitational field generated by the point mass near its world line at the black hole horizon. By applying the standard field-theoretical approach to the particle field, we compute the corresponding partial energy and find that it matches the constant multipole contribution.

gr-qc↗

arXiv2025

Electromagnetic radiation from circular orbits in Schwarzschild--de Sitter spacetime

We investigate the electromagnetic radiation emitted by a charged particle orbiting a four-dimensional Schwarzschild--de Sitter black hole using a semiclassical approach. We calculate the probability amplitude for the charged particle to emit a photon, from which we derive the emitted power and spectral distributions. The results are compared with those obtained for scalar fields, considering both minimal and nonminimal coupling, as well as the corresponding electromagnetic case in the Schwarzschild spacetime. It is found that the total electromagnetic power is approximately twice that of the scalar field with conformal coupling for orbits with low angular velocity, similar to the Schwarzschild case, whereas for minimal coupling, the scalar power can even exceed the electromagnetic power. We also investigate the spectral distributions and possible synchrotron emission by orbits near the photon sphere. The electromagnetic case has a much broader frequency spectrum, with a non-negligible lower multipole contribution.

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arXiv2024

Nonminimally coupled scalar field in Schwarzschild--de Sitter spacetime: Geodesic synchrotron radiation

We analyze the scalar radiation emitted by a source interacting with a nonminimally coupled scalar field in four-dimensional Schwarzschild--de Sitter spacetime. We obtain the emission probability using quantum field theory in curved spacetimes at tree level. We find that the source emits synchrotron-type radiation for orbits near the photon sphere for all allowed values of the parameters. We also find that the emitted power strongly depends on the coupling to the curvature scalar. In particular, the previously observed enhancement in the contribution of lower multipoles to the emitted power in this spacetime with minimal coupling is absent when conformal coupling is considered.

gr-qc↗

arXiv2024

Semiclassical bremsstrahlung from a charge radially falling into a Schwarzschild black hole

A semiclassical investigation of the electromagnetic radiation emitted by a charged particle in a radially freely falling motion in Schwarzschild spacetime is carried out. We use quantum field theory at tree level to obtain the one-particle-emission amplitudes. We analyze and compare the energy spectrum and total energy released, which are calculated from these amplitudes, for particles with varying initial positions and for particles originating from infinity with varying kinetic energy. We also compare the results with those due to a falling charged "string" extended in the radial direction.

gr-qc↗

arXiv2024

Gravitational bremsstrahlung and the Fulling-Davies-Unruh thermal bath

The electromagnetic radiation emitted by an accelerated charged particle can be described theoretically as the interaction of the charge with the so-called Fulling-Davies-Unruh thermal bath in the coordinate frame co-accelerated with the charge. We present a similar analysis on the gravitational radiation from a classical point mass uniformly accelerated, being pulled by a string satisfying the weak energy condition. In particular, we derive the interaction rate (with fixed transverse momentum) of this system of the point mass and string in the Fulling-Davies-Unruh thermal bath in the co-accelerated frame and show that it equals the graviton emission rate calculated in the standard method in Minkowski spacetime.

gr-qc↗

arXiv2020

Synchrotron geodesic radiation in Schwarzschild-de Sitter spacetime

We analyze the scalar radiation emitted by a source in geodesic circular orbits around a Schwarzschild-de Sitter black hole. We obtain the emitted power using quantum field theory in curved spacetimes framework at tree level. We compare our results with the scalar synchrotron radiation in Schwarzschild spacetime.

gr-qc↗