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J. Furtado

Publications and source records attributed to J. Furtado.

At least 19 recordsLinked to original sources

White Dwarf Stellar Structure from Effective Polymer Geometry in Loop Quantum Gravity

We construct an effective Tolman Oppenheimer Volkoff system for cold carbon white dwarfs using the areal radius form of a polymer metric sector motivated by loop quantum gravity. The two asymptotic mass parameters of the geometry are retained in the stellar prescription through $M_B\rightarrow m(R)$ and $M_W=\eta m(R)$, while the polymer amplitude is controlled by $A_\lambda$. The matter sector is kept fixed and is described by the Chandrasekhar equation of state and by the same carbon model with the Coulomb lattice correction. The resulting equations recover the general relativistic TOV system and the symmetric polymer limit. For the undeformed sequences we obtain $M_{\max}=1.4166\,M_\odot$ for the Chandrasekhar model and $M_{\max}=1.3850\,M_\odot$ when the lattice correction is included. Turning on $A_\lambda$ shifts the massive part of the equilibrium sequence upward without stiffening the equation of state, reaching $M_{\max}=1.7125\,M_\odot$ and $1.6907\,M_\odot$ at $A_\lambda=100$ for the two matter models. These configurations remain within the matter domain imposed by the inverse beta decay boundary used in the scan. The asymmetric ratio $\eta=M_W/M_B$ changes the metric function near the polymer transition region, but its effect on white dwarf observables is small: across the selected configurations, $M_{\max}$ changes by less than $0.1\%$ and the corresponding radius by less than $0.33\%$. The calculation therefore identifies $A_\lambda$ as the parameter controlling the super Chandrasekhar displacement of the mass radius relation, while $\eta$ acts mainly as a geometric asymmetry parameter in the low compactness regime probed by white dwarfs.

astro-ph.SR

Junction Conditions, Radial Stability, Thermodynamics, Optical Geometry and Appearance of Polymer-Quintessence Thin-Shell Wormholes

Thin-shell wormholes built from effective black hole geometries are sensitive not only to the lapse function but also to the choice of areal radius. We construct a reflection-symmetric thin-shell wormhole from the positive-lapse sector of a polymer black hole surrounded by Kiselev-type quintessence and keep the nonareal angular function throughout the junction, stability, thermodynamic, and optical analyses. The Israel junction conditions give a negative surface energy density for every static throat on the positive branch, while the tangential null and intrinsic strong energy combinations are controlled by the local lapse slope. The radial dynamics is written as an effective-potential problem in which the nonareal sector produces a momentum-flux term and modifies the local stability criterion for surface equations of state with explicit radius dependence. For the sampled calibrated configurations, the linear barotropic and variable phantomlike closures remain locally unstable, whereas the variable Chaplygin gas admits finite linear radial stability windows. The same geometric correction also modifies the local first-law balance and shell entropy bookkeeping, while the optical analysis shows that cross-throat propagation generates additional inner image branches despite the wormhole and black hole geometries sharing the same exterior critical curve. These results identify how polymer corrections and a quintessence environment jointly reorganize the matter content, radial response, thermodynamic bookkeeping, and optical appearance of the resulting thin-shell wormhole.

gr-qc

Fermion-fermion scattering in a Rarita-Schwinger model with Yukawa-like interaction

In this work, we investigate the scattering of spin-$3/2$ fermionic particles mediated by a Yukawa-like coupling in the context of the massive Rarita-Schwinger model. The interaction is introduced by replacing $m \to m_{\psi} + g\phi$ in the free spin-$3/2$ Lagrangian. The analysis is performed at both zero and finite temperatures. In the latter case, thermal effects are incorporated using the Thermofield Dynamics (TFD) formalism. In both regimes, we obtain the differential and total cross sections and examine their behavior in the short-range ($m_{\phi} \neq 0$) and long-range ($m_{\phi} = 0$) limits, in order to analyze the influence of zero- and finite-temperature effects.

hep-th

Rarita-Schwinger model in Very Special Relativity

In this work, we investigate vacuum polarization in the Rarita-Schwinger model within the framework of Very Special Relativity. We examine both massive and massless spin-3/2 fields coupled to the Maxwell field. The Mandelstam-Leibbrandt prescription is applied in order to evaluate the one-loop integrals, and we work within the SIM(2) limit.

hep-th

Polymer Black Hole Surrounded by Quintessence

In this paper, we study the polymer black hole solution surrounded by a quintessence field. The influence of quintessence on the polymer black hole is investigated through its thermodynamic properties, such as the Hawking temperature, entropy, and specific heat, which allow us to address the question of thermodynamic stability. We then calculate bounds on the electromagnetic greybody factors and photon emission rates of the black hole, highlighting the interplay between quintessence and quantum gravity effects in determining these phenomena. We also examine the effects of quintessence and quantum gravity on the geodesics and shadows of massless particles around the black hole. Our results are further compared with observational data of the Sagittarius A black hole from the Event Horizon Telescope (EHT) collaboration.

gr-qc

Dymnikova Black Hole Surrounded by Quintessence

The Dymnikova black hole (BH) is a regular solution that interpolates between a de Sitter core near the origin and a Schwarzschild-like behavior at large distances. In this work, we investigate the properties of a Dymnikova BH immersed in a quintessential field, characterized by the state parameter $\omega$ and a normalization constant $c$. We explore the thermodynamic behavior, null geodesics, scalar quasinormal modes and shadow profiles for this model. Our analysis shows that the presence of quintessence alters the Hawking temperature and specific heat, leading to parameter-dependent phase transitions. The null geodesics and corresponding black hole shadows are also found to be sensitive to the model parameters, especially $\omega$ and $c$. This sensitivity influences light deflection and shadow size. Furthermore, we compute the scalar quasinormal modes and observe that quintessence tends to enhance the damping of the modes, indicating greater stability under perturbations.

gr-qc

Lorentz-violating QED inspired superconductivity

We studied a Lorentz-violating inspired Ginzburg-Landau model for superconductivity where we considered a CPT-odd contribution given by $(k_{AF})^{\mu}$, also known as the Carroll-Field-Jackiw term. In the static limit of the equations, we could find a pair of modified Ginzburg-Landau equations. Furthermore, these equations were reduced to the London equation for the magnetic field when assumed that the characteristic length of the order parameter is much smaller than the characteristic length of the magnetic field, i.e. the London penetration length. Our numerical solutions showed a simple Meissner state when this new term is small compared to $\lambda_L$ and a phase transition into phases with strong in-plane currents and anomalous vortices for large contributions. This model becomes useful in exemplifying the changes in the phenomenology of superconductors when the setup of the system shows an important breakdown of Lorentz invariance. Based on these results, we discuss how such models might be the hallmark of unusual superconducting states where there is a direction where the system shows stratification, as in anapole superconductors UTe$_2$.

cond-mat.supr-con

Non-hermitian phase transitions on a generalized Ellis-Bronnikov wormhole bridge

In this paper, we investigate the emergence of non-Hermitian phase transitions on a quantum wormhole surface. We consider a single fermion whose dynamics are governed by the Dirac equation confined to move on a quantum wormhole surface. The effects of the geometry are taken into account using the tetrad formalism and the spin connection. The Dirac equation gives rise to two coupled first-order differential equations for each spinor component. The eigenvalues and eigenfunctions for each spinor component are computed numerically, and the non-Hermitian phase transitions are investigated in terms of the geometric features of the wormhole and the magnitude of the imaginary component of the mass.

gr-qc

Bhabha-like scattering in the Rarita-Schwinger model at finite temperature

In this paper, we study a Bhabha-like scattering in a massive Rarita-Schwinger model at finite temperature. The analysis is conducted at the tree level and addresses temperature effects through the thermofield dynamics formalism. We consider the usual fermion-antifermion into fermion-antifermion scattering and compute the cross-section in order to investigate the influence of the finite temperature effects.

hep-th

Electronic states in a bilayer graphene quantum ripple

In this paper, we investigate the influence of the geometry in the electronic states of a quantum ripple surface. We have considered an electron governed by the spinless stationary Schr\"{o}dinger equation constrained to move on the ripple surface due to a confining potential from which the Da Costa potential emerges. We investigate the role played by the geometry and orbital angular momentum on the electronic states of the system.

cond-mat.mes-hall

Enhanced Quantum Mpemba Effect with Squeezed Thermal Reservoirs

The phenomenon where a quantum system can be exponentially accelerated to its stationary state has been referred to as the Quantum Mpemba Effect (QMpE). Due to its analogy with the classical Mpemba effect, hot water freezes faster than cold water, this phenomenon has garnered significant attention. Although QMpE has been characterized and experimentally verified in different scenarios, the sufficient and necessary conditions to achieve such a phenomenon are still under investigation. In this paper, we address a sufficient condition for QMpE through a general approach for open quantum system dynamics. With the help of the Mpemba parameter introduced in this work to quantify how strong the QMpE can be, we discuss how our conditions can predict and explain the emergence of weak and strong QMpE in a robust way. As an application, by harnessing the intrinsic non-classical nature of squeezed thermal environments, we show how enhanced QMpE can be effectively induced when our conditions are met. We demonstrate that when the system interacts with thermal reservoirs, a hot qubit freezes faster than a cold qubit in the presence of squeezing. Our results provide tools and new insights, opening a broad avenue for further investigation at the most fundamental levels of this peculiar phenomenon in the quantum realm.

quant-ph

Multiple non-hermitian phase transitions on quantum torus surface

In this paper we investigate the arising of non-hermitian phase transitions on quantum torus surfaces. We consider a single fermion whose dynamics is governed by the Dirac equation confined to move on a quantum torus surface. The effects of the geometry are take into account by using the tetrad formalism and the spin connection. The Dirac equation gives rise to two coupled first-order differential equations for each spinor component. The eigenvalues and eigenfunctions for each spinor component are computed numerically and the non-hermitian phase transitions are investigated in terms of the geometric features of the torus and the magnitude of the imaginary component of the mass.

quant-ph

Meson scattering in a non-minimally Lorentz-violating scalar QED at finite temperature

In this paper we study meson scattering in a non-minimally Lorentz-violating scalar QED at finite temperature. The meson scatterings were investigated in tree level and the finite temperature effects were addressed by using the thermofield dynamics formalism. We have considered three types of scattering, namely, meson-antimeson of $a$-type into meson-antimeson of $b$-type, meson-antimeson of $a$-type into meson-antimeson of $a$-type and meson-meson of $a$-type into meson-meson of $a$-type. For each scattering we have computed the cross section in order to investigate the influence of the finite temperature effects.

hep-th

Black string solutions in Lifshitz spacetime

In this paper we study black string solutions considering the Lifshitz anisotropic scaling. We have shown that a new class of asymptotically Lifshitz solutions can be generated by an Einstein-Maxwell-Dilaton theory with a cosmological constant. In the limit where we recover conformal scale invariance, we retrieve the usual black string solution. Furthermore, we demonstrated that to incorporate the effects of electric charge in the black string, at least two independent gauge fields coupled to the dilaton field are necessary. The charged black string solution exhibits new horizons that depend on the potential in Lifshitz exponent $z$. The stability of these new solutions is investigated through the thermodynamic analysis of the charged black string. The temperature, entropy, and heat capacity indicate that these modified black strings are thermodynamically stable.

gr-qc

Strain effects on the electronic properties of a graphene wormhole

In this work, we explore the strain and curvature effects on the electronic properties of a curved graphene structure, called the graphene wormhole. The electron dynamics is described by a massless Dirac fermion containing position--dependent Fermi velocity. In addition, the strain produces a pseudo--magnetic vector potential to the geometric coupling. For an isotropic strain tensor, the decoupled components of the spinor field exhibit a supersymmetric (SUSY) potential, depending on the centrifugal term and the external magnetic field only. In the absence of a external magnetic field, the strain yields to an exponential damped amplitude, whereas the curvature leads to a power--law damping of the wave function. The spin--curvature coupling breaks the chiral symmetry between the upper and the lower spinor component, which leads to the increasing of the wave function on either upper or lower region of the wormhole, i.e., depending on the spin number. By adding an uniform magnetic field, the effective potential exhibits an asymptotic quadratic profile and a spin--curvature barrier near the throat. As a result, the bound states (Landau levels) are confined around the wormhole throat showing an asymmetric and spin--dependent profile.

cond-mat.mes-hall

Thermodynamics and Quasinormal Modes of the Dymnikova Black Hole in Higher Dimensions

In this study, we investigate the thermodynamic properties and quasinormal modes of Dymnikova black holes within the context of higher dimensions in Einstein's general theory of relativity. We calculate the thermodynamic parameters, including the Hawking temperature and heat capacity, which allowed us to investigate the black hole's stability. Lastly the quasinormal modes with the WKB formula were calculated.

gr-qc

Massless fermions in black string spacetime

In this paper we investigate the behaviour of massless fermions in the black string spacetime by computing the eigenvalues and eigenfunctions of the Weyl equations. These solutions allowed us to study the behaviour of such massless fermions in terms of the cosmological constant, the black string's mass and the radial distance of the particle from the black string. The solutions, written in terms of Parabolic Cylinder functions and Laguerre polynomials, were obtained for a particle far from the black string and around the horizon event. For the particle around the event horizon, for all configuration of parameters, the energy eigenvalues are complex-valued, indicating QNM similarly to the case of spherical black holes. For the particle far from the black string, the energies derived from the Weyl equation set up conditions on the parameters in order to keep the energy as a real valued parameter.

hep-th

Anisotropic Ginzburg-Landau model for superconductivity with five-dimensional operators

This paper presents the effects of non-minimal Lorentz-violation operators in superconductivity. By constructing a Lorentz-Violating Ginzburg-Landau theory of superconductivity with a five-dimensional operator, we discuss the influence of higher dimensional Lorentz-Violating operators in the London's depth penetration, in the coherence length and critical magnetic field.

hep-th