arXiv subjects

H. F. Santana Mota

Publications and source records attributed to H. F. Santana Mota.

15 recordsLinked to original sources

arXiv2026

Induced current by a magnetic flux in $(1+2)-$dimensional conical spacetime in a Ho{ř}ava-Lifshitz Lorentz-violating scenario

We investigate the vacuum expectation value of bosonic current induced by a magnetic flux in a $(2+1)-$dimensional conical spacetime in the presence of a circular boundary, in a Ho{ř}ava-Lifshitz Lorentz violation symmetry scenario. We assume that the circular boundary is concentric with magnetic flux, and the massive scalar quantum field obeys the Robin boundary condition on the boundary. In order to develop this analysis, we calculate the positive frequency Wightman functions for both regions, inside and outside the boundary. Using these functions, we obtain analytical expressions for the vacuum expectation bosonic currents. As we will see, these functions are presented in the form of the sum of boundary-free and boundary-induced parts. As to the boundary-induced currents, some asymptotic behaviors are investigated for specific limiting cases; moreover, in order to provide a better understanding about the behavior of the currents, some plots are given.

hep-th↗

arXiv2025

Cylindrical boundary induced current in the cosmic string spacetime

In this paper we investigate the vacuum current associated with a charged bosonic field operator, induced by a cylindrical boundary in the idealized cosmic string spacetime. In this setup we assume that the cylindrical boundary is coaxial with the string, that by its turn carry a magnetic flux along its core. In order to develop this analysis, we calculate the positive frequency Wightman functions for both regions, inside and outside the boundary. Moreover, we assume that the bosonic field obeys the Robin boundary condition on the cylindrical shell. Using this approach, the analytical expressions for the vacuum bosonic currents are presented in the form of the sum of boundary-free and boundary-induced parts. Because the boundary-free contribution is very well established in literature, our focus here is in the boundary-dependent part. As we will see, our general results are presented in a cylindrically symmetric static structure. Some asymptotic behaviors for the boundary-induced vacuum currents are investigated in various limiting cases. In order to provide a better understanding of these currents, we provide some graphs exhibiting their behavior as function of the distance to the string's core, and on the intensity of the magnetic flux running along it. These plots also present how the parameter associated with the planar angle deficit interfere in the intensity of the corresponding current.

hep-th↗

arXiv2024

Current density induced by a cosmic string in de Sitter spacetime in the presence of two flat boundaries

In this paper, we investigate the vacuum bosonic current density induced by a carrying-magnetic-flux cosmic string in a $(D+1)$-de Sitter spacetime considering the presence of two flat boundaries perpendicular to it. In this setup, the Robin boundary conditions are imposed on the scalar charged quantum field on the boundaries. The particular cases of Dirichlet and Neumann boundary conditions are studied separately. Due to the coupling of the quantum scalar field with the classical gauge field, corresponding to a magnetic flux running along the string's core, a nonzero vacuum expectation value for the current density operator along the azimuthal direction is induced. The two boundaries divide the space in three regions with different properties of the vacuum states. In this way, our main objective is to calculate the induced currents in these three regions. In order to develop this analysis we calculate, for both regions, the positive frequency Wightman functions. Because the vacuum bosonic current in dS space has been investigated before, in this paper we consider only the contributions induced by the boundaries. We show that for each region the azimuthal current densities are odd functions of the magnetic flux along the string. To probe the correctness of our results, we take the particular cases and analyze some asymptotic limits of the parameters of the model. Also some graphs are presented exhibiting the behavior of the current with relevant physical parameter of the system.

hep-th↗

arXiv2024

Quantum Brownian motion induced by a scalar field in Einstein universe under Dirichlet and Neumann boundary conditions

In this paper, the Quantum Brownian motion of a point particle induced by the quantum vacuum fluctuations of a real massless scalar field in Einstein universe under Dirichlet and Neumann boundary conditions is studied. Using the Wightman functions, general expressions for the renormalized dispersion of the physical momentum are derived. Distinct expressions are found for the dispersion associated with each component of the particle physical momentum, indicating that the global properties of homogeneity and isotropy of space are lost, as a consequence of the introduced boundary conditions. Divergences also arise and are related to the compact nature of Einstein universe and the introduced boundary conditions.

gr-qc↗

arXiv2024

Quantum Brownian motion induced by a scalar field in Einstein's universe

The Brownian motion of a point particle induced by quantum vacuum fluctuations of a massless real scalar field in Einstein's universe is studied. By assuming the small displacement condition, the dispersion in the momentum and position of a point particle coupled to the massless scalar field are obtained. As a consequence of the homogeneity and isotropy properties of the Einstein's Universe, we find that all components of these physical observables are identical. We also examine divergent behaviors associated to the physical momentum and position dispersions, which we attribute to the $R^1\times S^3$ compact topology of the spacetime. Finally, based on the small displacement condition assumed, we analyze the limit of validity of our investigation.

gr-qc↗

arXiv2023

Bosonic Casimir effect in an aether-like Lorentz-violating scenario with higher order derivatives

In this paper we investigate the bosonic Casimir effect in a Lorentz-violating symmetry scenario. The theoretical model adopted consists of a real massive scalar quantum field confined in a region between two large parallel plates, having its dynamics governed by a modified Klein-Gordon equation that presents a Lorentz symmetry breaking term. In this context we admit that the quantum field obeys specific boundary conditions on the plates. The Lorentz-violating symmetry is implemented by the presence of an arbitrary constant space-like vector in a CPT-even aether-like approach, considering a direct coupling between this vector with the derivative of the field in higher order. The modification on the Klein-Gordon equation produces important corrections on the Casimir energy and pressure. Thus, we show that these corrections strongly depend on the order of the higher derivative term and the specific direction of the constant vector, as well as the boundary conditions considered.

hep-th↗

arXiv2022

Fermionic vacuum polarization induced by a non-Abelian vortex

In this paper, we analyze the fermionic condensate (FC) and the vacuum expectation value (VEV) of the energy-momentum tensor associated with an isospin-$1/2$ charged massive fermionic field induced by the presence of a $SU(2)$ vortex, taking into account the effect of the conical geometry produced by this object. We consider the vortex as an idealized topological defect, i.e., very thin, straight and carrying a magnetic flux running along its core. Besides the direct coupling of the fermionic field with the iso-vector gauge field, we also admit the coupling with the scalar sector of the non-Abelian vortex system, expressed as a vector in the three-dimensional isospace. Due to this interaction, the FC is expressed as the sum of two contributions associated with the two different effective masses for the $\pm 1/2$ fermionic components of the isospin operator, $τ^3/2$. The VEV of the energy-tensor also presents a similar structure. The vacuum energy density is equal to the radial and axial stresses. As to the azimuthal one, it is expressed in terms of the radial derivative of energy-density. Regarding to the magnetic flux, both, the FC and the VEV of the energy-momentum tensor, can be positive or negative. Another interesting consequence of the interaction with the bosonic sector, the FC and VEV of the energy-momentum tensor, present different intensity for different values of the ratio between the scalar coupling constant and the mass of the fermionic field. This is a new feature that the system presents.

hep-th↗

arXiv2022

Quantum Brownian motion for a particle in analog expanding cosmologies in the presence of disclination

In this paper we study the quantum brownian motion of a scalar point particle in the analog Friedman-Robertson-Walker spacetime in the presence of a disclination, in a condensed matter system. The analog spacetime is obtained as an effective description of a Bose-Einstein condensate in terms of quantum excitations of sound waves, named phonons. The dynamics of the phonons is described by a massless real scalar field whose modes are also subjected to a quasi-periodic condition. In this sense, we find exact solutions for the real scalar field in this scenario and calculate the two-point function which makes possible to analyze the mean squared velocity dispersion of the particle in all directions. We, thus, analyze some interesting particular cases and show some graphs where it is possible to see the consistency of our results.

gr-qc↗

arXiv2020

Casimir energy and topological mass for a massive scalar field with Lorentz violation

A Lorentz symmetry violation aether-type theoretical model is considered to investigate the Casimir effect and the generation of topological mass associated with a self-interacting massive scalar fields obeying Dirichlet, Newman and mixed boundary conditions on two large and parallel plates. By adopting the path integral approach we found the effective potential at one- and two-loop corrections which provides both the energy density and topological mass when taken in the ground state of the scalar field. We then analyse how these quantities are affected by the Lorentz symmetry violation and compare the results with previous ones found in literature.

hep-th↗

arXiv2020

Quantum vacuum fluctuation effects in a quasi-periodically identified conical spacetime

We consider a quasi-periodically identified conical spacetime, like the one of a cosmic string or disclination, to investigate nonzero averaged quantum vacuum fluctuations effects on the energy-momentum tensor and induced current density associated with a charged scalar field. We obtain exactly closed analytical expressions for the two-point Wightman function and the vacuum expectation value of the field squared, as well as for all components of the energy-momentum tensor. As to the induced current density, due to the quasi-periodic condition used, the only nonzero averaged component found is the azimuthal one. We also compare our results with previous ones found in literature.

hep-th↗

arXiv2020

Scalar self-interaction in the spacetime of a cosmic dispiration

In the present paper we investigate the classical self-interaction associated with a charged scalar point particle placed at rest in the gravitational field of a linear topological defect known in literature as cosmic dispiration, a combination of a cosmic string with a screw dislocation. We found exact expressions for the Green's function and, consequently, for the self-energy by considering both massive and massless scalar point particles. We present numerical graphs and analyze the nature of the self-interactions in the cosmic dispiration spacetime itself and in the cases of pure screw dislocation and cosmic string spacetimes.

hep-th↗

arXiv2019

Vacuum expectation value of the energy-momentum tensor in a higher dimensional compactified cosmic string spacetime

The main objective of this paper is to analyze the vacuum expectation value (VEV) of the energy-momentum tensor (EMT) associated with a charged scalar quantum field in a high-dimensional cosmic string spacetime admitting the presence of a magnetic flux running along the string's core. In addition, we also assume that the coordinate along the string's axis is compactified to a circle and presents an extra magnetic flux running along its center. This compactification is implemented by imposing a quasiperiodic condition on the field with an arbitrary phase $β$. The calculation of the VEV of the EMT and field squared, are developed by using the positive-energy Wightman function. The latter is constructed by the mode sum of the complete set of normalized bosonic wave-functions. Due to the compactification, two distinct contributions take place. The first one corresponds to the VEV in a cosmic string spacetime without compactification considering the magnetic interaction. So, this term presents a contribution due to the non-trivial topology of the conical space, and an additional contribution due to the interaction between the scalar field with the magnetic flux. The latter is a periodic function of the magnetic flux with period equal to the quantum flux, $Φ_0=2π/e$, and corresponds to a Aharanov-Bhom type contribution. The second contribution is induced by the compactification itself and depends on the magnetic flux along the string's core. It is also an even function of the magnetic flux enclosed by the string axis. Some asymptotic expressions for the VEVs of the energy-momentum tensor and field squared are provided for specific limiting cases of the physical parameter of the model.

hep-th↗

arXiv2015

Induced vacuum bosonic current in a compactified cosmic string spacetime

We analyze the bosonic current densities induced by a magnetic flux running along an idealized cosmic string considering that the coordinate along its axis is compactified. We also consider the presence of a magnetic flux enclosed by the compactificatified axis. To develop this analysis, we calculate the complete set of normalized bosonic wave functions obeying a quasiperiodicity condition along the compactified dimension. We show that in this context only the azimuthal and axial currents take place.

hep-th↗

arXiv2015

Induced vacuum bosonic current by magnetic flux in a higher dimensional compactified cosmic string spacetime

In this paper, we analyse the bosonic current densities induced by a magnetic flux running along an idealized cosmic string in a high-dimensional spacetime, admitting that the coordinate along the string's axis is compactified. Additionally we admit the presence of an magnetic flux enclosed by the compactification axis. In order to develop this analysis we calculate the complete set of normalized bosonic wave-functions obeying a quasiperiodicity condition, with arbitrary phase $β$, along the compactified dimension. In this context, only azimuthal and axial currents densities take place. As to the azimuthal current, two contributions appear. The first contribution corresponds to the standard azimuthal current in a cosmic string spacetime without compactification, while the second contribution is a new one, induced by the compactification itself. The latter is an even function of the magnetic flux enclosed by the string axis and is an odd function of the magnetic flux along its core with period equal to quantum flux, $Φ_0=2π/e$. On the other hand, the nonzero axial current density is an even function of the magnetic flux along the core of the string and an odd function of the magnetic flux enclosed by it. We also find that the axial current density vanishes for untwisted and twisted bosonic fields in the absence of the magnetic flux enclosed by the string axis. Some asymptotic expressions for the current density are provided for specific limiting cases of the physical parameter of the model.

hep-th↗

arXiv2015

Big-Bang Nucleosynthesis and Gamma-Ray Constraints on Cosmic Strings with a large Higgs condensate

We consider constraints on cosmic strings from their emission of Higgs particles, in the case that the strings have a Higgs condensate with amplitude of order the string mass scale, assuming that a fraction of the energy of condensate can be turned into radiation near cusps. The injection of energy by the decaying Higgs particles affects the light element abundances predicted by standard Big-Bang Nucleosynthesis (BBN), and also contributes to the Diffuse Gamma-Ray Background (DGRB) in the universe today. We examine the two main string scenarios (Nambu-Goto and field theory), and find that the primordial Helium abundance strongly constrains the string tension and the efficiency of the emission process in the NG scenario, while the strongest BBN constraint in the FT scenario comes from the Deuterium abundance. The Fermi-LAT measurement of the DGRB constrains the field theory scenario even more strongly than previously estimated from EGRET data, requiring that the product of the string tension μ and Newton's constant G is bounded by Gμ < 2.7x10^{-11}β_{ft}^{-2}, where β_{ft}^2 is the fraction of the strings' energy going into Higgs particles.

hep-ph↗