arXiv subjects

F. A. Brito

Publications and source records attributed to F. A. Brito.

At least 73 records · Page 4Linked to original sources

arXiv2019

Brazilian Community Report on Dark Matter

This white paper summarizes the activities of the Brazilian community concerning dark matter physics and highlights the importance of financial support to Brazilian groups that are deeply involved in experimental endeavours. The flagships of the Brazilian dark matter program are the Cherenkov Telescope Array, DARKSIDE, SBN and LHC experiments, but we emphasize that smaller experiments such as DAMIC and CONNIE constitute important probes to dark sectors as well and should receive special attention. Small experimental projects showing the potential to probe new regions of parameter space of dark matter models are encouraged. On the theoretical and phenomenological side, some groups are devoted to astrophysical aspects such as the dark matter density profile while others explore the signature of dark matter models at colliders, direct and indirect detection experiments. In summary, the Brazilian dark matter community that was born not long ago has grown tremendously in the past years and now plays an important role in the hunt for a dark matter particle.

hep-ph↗

arXiv2019

Modeling dark sector in Horndeski gravity at first-order formalism

We investigate a cosmological scenario by finding solutions using first-order formalism in the Horndeski gravity that constrains the superpotential and implies that no free choice of scalar potential is allowed. Despite this we show that a de Sitter phase at late-time cosmology can be realized, where the dark energy sector can be identified. The scalar field equation of state tends to the cosmological scenario at present time and allows us to conclude that it can simulate the dark energy in the Horndeski gravity.

hep-th↗

arXiv2019

Quantum-corrected rotating acoustic black holes in Lorentz-violating background

In this paper we explore the effect of the generalized uncertainty principle and modified dispersion relation to compute Hawking radiation from a rotating acoustic black hole in the tunneling formalism by using the Wentzel-Kramers-Brillouin (WKB) approximation applied to the Hamilton-Jacobi method. The starting point is to consider the planar acoustic black hole metric found in a Lorentz-violating Abelian Higgs model. In our analyzes we investigate quantum corrections for the Hawking temperature and entropy. A logarithmic correction and an extra term that depends on a conserved charge were obtained. We also have found that the changing in the Hawking temperature ${\cal T}_H$ for a dispersive medium due to a Lorentz-violating background accounts for supersonic velocities in the general form $(v_g-v_p)/v_p = Δ{\cal T}_H/{\cal T}_H\sim10^{-5}$ in Bose-Einstein-Condensate (BEC) systems.

hep-th↗

arXiv2019

Gravitational axial perturbations and quasinormal modes of loop quantum black holes

Loop Quantum Gravity (LQG) is a theory that proposes a way to model the behavior of the spacetime in situations where its atomic characteristic arises. Among these situations, the spacetime behavior near the Big Bang or black hole's singularity. The detection of gravitational waves, on the other hand, has opened the way to new perspectives in the investigation of the spacetime structure. In this work, by the use of a WKB method introduced by Schutz and Will \cite{Schutz:1985zz}, and after improved by Iyer and Will \cite{s.iyer-prd35}, we study the gravitational wave spectrum emitted by loop quantum black holes, which correspond to a quantized version of the Schwarzschild spacetime by LQG techniques. From the results obtained, loop quantum black holes have been shown stable under axial gravitational perturbations.

gr-qc↗

arXiv2018

Absorption and scattering of a black hole with a global monopole in f(R) gravity

In this paper we consider the solution of a black hole with a global monopole in $f(R)$ gravity and apply the partial wave approach to compute the differential scattering cross section and absorption cross section. We show that in the low-frequency limit and at small angles the contribution to the dominant term in the scattering/absorption cross section is modified by the presence of the global monopole and the gravity modification. In such limit, the absorption cross section shows to be proportional to the area of the event horizon.

hep-th↗

arXiv2018

The entropy of an acoustic black hole in neo-Newtonian theory

In this paper we consider the metric of a 2+1-dimensional rotating acoustic black hole in the neo-Newtonian theory to compute the Hawking temperature and applying the quantum statistical method, we calculate the statistical entropy using a corrected state density due to the generalized uncertainty principle (GUP). In our calculations we have shown that the obtained entropy is finite and correction terms are generated. Moreover, the computation of the entropy for this method does not present logarithmic corrections.

hep-th↗

arXiv2018

Harmonic oscillators from displacement operators and thermodynamics

In this investigation, the displacement operator is revisited. We established a connection between the Hermitian version of this operator with the well-known Weyl ordering. Besides, we characterized the quantum properties of a simple displaced harmonic oscillator, as well as of a displaced anisotropic two-dimensional non-Hermitian harmonic oscillator. By constructing the partition functions for both harmonic oscillators, we were able to derive several thermodynamic quantities from their energy spectra. The features of these quantities were depicted and analyzed in details.

cond-mat.stat-mech↗

arXiv2018

Lorentz-violating dimension-five operator contribution to the black body radiation

We investigate the thermodynamics of a photon gas in an effective field theory model that describes Lorentz violations through dimension-five operators and Horava-Lifshitz theory. We explore the electrodynamics of the model which includes higher order derivatives in the Lagrangian that can modify the dispersion relation for the propagation of the photons. We shall focus on the deformed black body radiation spectrum and modified Stefan-Boltzmann law to address the allowed bounds on the Lorentz-violating parameter.

hep-th↗

arXiv2018

Soliton solutions in two-dimensional Lorentz-violating higher derivative scalar theory

This paper shows a new approach to obtain analytical topological defects of a 2D Myers-Pospelov Lagrangian for two scalar fields. Such a Lagrangian presents higher-order kinetic terms, which lead us to equations of motion which are non-trivial to be integrated. Here we describe three possible scenarios for the equations of motion, named by timelike, spacelike and lightlike respectively. We started our investigation with a kink-like travelling wave Ansatz for the free theory, which led us to constraints for the dispersion relations of each scenario. We also introduced a procedure to obtain analytical solutions for the general theory in the three mentioned scenarios. We exemplified the procedure and discussed the behavior of the defect solutions carefully. It is remarkable that the methodology presented in this study led to analytical models, despite the complexity of the equations of motion derived from the 2D Myers-Pospelov Lagrangian. The methodology here tailored can be applied to several Lagrangians with higher-order derivative terms.

hep-th↗

arXiv2018

CMB constraints on $β$-exponential inflationary models

We analyze a class of generalized inflationary models proposed in Ref. [1], known as $β$-exponential inflation. We show that this kind of potential can arise in the context of brane cosmology, where the field describing the size of the extra-dimension is interpreted as the inflaton. We discuss the observational viability of this class of model in light of the latest Cosmic Microwave Background (CMB) data from the Planck Collaboration through a Bayesian analysis, and impose tight constraints on the model parameters. We find that the CMB data alone prefer \textit{weakly} the minimal standard model ($Λ$CDM) over the $β$-exponential inflation. However, when current local measurements of the Hubble parameter, $H_0$, are considered, the $β$-inflation model is {\it moderately} preferred over the $Λ$CDM cosmology, making the study of this class of inflationary models interesting in the context of the current $H_0$ tension.

astro-ph.CO↗

arXiv2018

Quantum correction to the entropy of noncommutative BTZ black hole

In this paper we consider the generalized uncertainty principle (GUP) in the tunneling formalism via Hamilton-Jacobi method to determine the quantum-corrected Hawking temperature and entropy for noncommutative BTZ black hole. In our results we obtain several types of corrections including the expected logarithmic correction to the area entropy associated with the noncommutative BTZ black holes. We also show that the area entropy product of the noncommutative BTZ black holes is dependent on mass and by analyzing the nature of the specific heat capacity we have observed that the noncommutative BTZ black hole is stable at some range of parameters.

hep-th↗

arXiv2017

Cosmology in the Universe with distance dependent Lorentz-violating bakground

We consider a cosmological setup with the inflaton field in the presence of a redshift dependent Lorentz-violating time-like background to address the inflationary regime and other phases of the Universe. We also show that the regime of dark energy at large distances (low redshifts) is essentially dominated by the presence of the Lorentz-violating background.

hep-th↗

arXiv2017

Lorentz invariance violation and simultaneous emission of electromagnetic and gravitational waves

In this work, we compute some phenomenological bounds for the electromagnetic and massive gravitational high-derivative extensions supposing that it is possible to have an astrophysical process that generates simultaneously gravitational and electromagnetic waves. We present Lorentz invariance violating (LIV) higher-order derivative models, following the Myers-Pospelov approach, to electrodynamics and massive gravitational waves. We compute the corrected equation of motion of these models, their dispersion relations and the velocities. The LIV parameters for the gravitational and electromagnetic sectors, $ξ_{g}$ and $ξ_γ$, respectively, were also obtained for three different approaches: luminal photons, time delay of flight and the difference of graviton and photon velocities. These LIV parameters depend on the mass scales where the LIV-terms become relevant, $M$ for the electromagnetic sector and $M_{1}$ for the gravitational one. We obtain, using the values for $M$ and $M_{1}$ found in the literature, that $ξ_{g}\sim10^{-2}$, which is expected to be phenomenologically relevant and $ξ_γ\sim10^{3}$, which cannot be suitable for an effective LIV theory. However, we show that $ξ_γ$ can be interesting in a phenomenological point of view if $M\gg M_{1}$. Finally the relation between the variation of the velocities of the photon and the graviton in relation to the speed of light was calculated and resulted in $Δv_{g}/Δv_γ\lesssim1.82\times 10^{-3}$.

hep-th↗

arXiv2017

Induction of the Lorentz-violating effective actions in quantum electrodynamics

We introduce a Lorentz-symmetry violating extended quantum electrodynamics (QED) which preserves gauge symmetry. The extended fermionic sector can radiatively induce an extended effective action which simultaneously displays the same electromagnetic terms present in the Carroll-Field-Jackiw, Myers-Pospelov and Aether actions.

hep-th↗

arXiv2017

Aharonov-Bohm effect for a fermion field in a planar black hole "spacetime"

In this paper we consider the dynamics of a massive spinor field in the background of the acoustic black hole spacetime. Although this effective metric is acoustic and describes the propagation of sound waves, it can be considered as a toy model for the gravitational black hole. In this manner, we study the properties of the dynamics of the fermion field in this "gravitational" rotating black hole as well as the vortex background. We compute the differential cross section through the use of the partial wave approach and show that an effect similar to the gravitational Aharonov-Bohm effect occurs for the massive fermion field moving in this effective metric. We discuss the limiting cases and compare the results with the massless scalar field case.

hep-th↗

arXiv2017

Two Dimensional Horava-Lifshitz Black Hole Solutions

In this paper we address the issue of black hole solutions in (1+1)-dimensional non-projectable Horava-Lifshitz gravity. We consider several models by considering different potentials in the scalar matter sector. We also consider the gravitational collapse of a distribution of pressureless dust filling a region in one-dimensional space. The time of the collapse can be faster or slower depending on the parameter $λ$ of the theory.

hep-th↗

arXiv2016

Localized four-dimensional gravity in the D-brane background with NS $B$ field

We calculate small correction terms to gravitational potential near $p$-branes embedded in a constant NS $B$ field background in the context of M-theory or string theory. The normalizable wave functions of gravity fluctuations around the brane describe only massive modes. We compute such wave functions analytically. We estimate the correction to gravitational potential for small and long distances, and show that there is an intermediate range of distances in which we can identify $4D$ gravity on the brane below a crossover scale given in terms of components of the $B$ field. The $4D$ gravity is metastable and for distances much larger than the crossover scale the $5D$ gravity is recovered.

hep-th↗

arXiv2016

Kondo effect from a Lorentz-violating domain wall description of superconductivity

We extend recent results on domain wall description of superconductivity in an Abelian Higgs model by introducing a particular Lorentz-violating term. The temperature of the system is interpreted through the fact that the soliton following accelerating orbits is a Rindler observer experiencing a thermal bath. We show that this term can be associated with the {\sl Kondo effect}, that is, the Lorentz-violating parameter is closely related to the concentration of magnetic impurities living on a superconducting domain wall. We also found that the critical temperature decreasing with the impurity concentration as a non single-valued function, for the case $T_K < T_{c0}$, develops a negative curvature and presents deviations from the Abrikosov and Gor'kov theory, a phenomenon already supported by experimental evidence.

hep-th↗