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Marco Maceda

Publications and source records attributed to Marco Maceda.

At least 19 recordsLinked to original sources
arXiv2024

Numerical study of the properties of a holographic superconductor from an anti-de Sitter-Einstein-Born-Infeld black hole with backreaction

We study numerically an $s$-wave holographic superconductor from an anti-de Sitter-Einstein-Born-Infeld black hole with backreaction in the context of the anti-de Sitter/conformal field theory (AdS/CFT) correspondence. By introducing a parameter $G$ to tune the effects of the backreaction, we can study non-perturbatively how the condensation and conductivity of the superconductor change as the backreaction increases. We find that for small values of $G$, increasing the nonlinearity of the Born-Infeld model makes the formation of the condensate harder -- consistent with previous results reported in the literature -- while for values of $G$ close to one, the opposite effect occurs; increasing the nonlinearity slightly facilitates its formation. This result is confirmed by making similar studies for the electrical conductivity of the superconductor and the penetration depth of the Meissner effect. Moreover, we analize in detail the superfluid density in these systems. We also determine how the ratio $\omega_g/T_c$ varies for different intensities of nonlinearity and backreaction, showing in particular that large deviations from the so-called universal value arise as backreaction becomes stronger.

hep-th↗
arXiv2023

Gravitational Waves from Thurston Geometries

It has been established that the famous three-dimensional Thurston geometries have four intrinsically Lorentzian analogs. We explore these spacetimes in three-dimensional general relativity nonminimally coupled to a scalar field together with electromagnetic matter. We find that three of these spacetimes support electromagnetic radiation, while, the other is partially sourced by a nonnull field and supports gravitational radiation. By addressing this problem we have also found a novel type of gravitational Cheshire effect.

gr-qc↗
arXiv2020

Nonlinear extensions of gravitating dyons: from NUT wormholes to Taub-Bolt instantons

Recent work has shown the existence of a unique nonlinear extension of electromagnetism which preserves conformal symmetry and allows for the freedom of duality rotations. Moreover, black holes and gravitational waves have been found to exist in this nonlinearly extended electrovacuum. We generalise these dyonic black holes in two major ways: with the relaxation of their horizon topology and with the inclusion of magnetic mass. Motivated by recent attention to traversable wormholes, we use this new family of Taub-NUT spaces to construct AdS wormholes. We explore some thermodynamic features by using a semi-classical approach. Our results show that a phase transition between the nut and bolt configurations arises in a similar way to the Maxwellian case.

gr-qc↗
arXiv2020

Black holes and gravitational waves sourced by non-linear duality rotation-invariant conformal electromagnetic matter

Maxwell's equations are invariant under both duality rotations and conformal transformations. Recently Bandos, Lechner, Sorokin, and Townsend have found a nonlinear generalisation of electrodynamics which possesses both of these symmetries. We couple this theory to General Relativity and explore self-gravitating configurations with a clear physical interpretation. We find charged black holes and exact gravitational waves. The black hole geometry is Reissner-Nordström, however, the non-linearity parameter acts as a screening factor allowing extremal configurations where the mass of the black hole is smaller than its charge. Furthermore, we also discuss the phenomenon of birefringence and determine the optical metrics associated to the propagation of photons.

gr-qc↗
arXiv2020

Shadow of a noncommutative inspired Einstein-Euler-Heisenberg black hole

Using a noncommutative inspired Einstein-Euler-Heisenberg black hole, we analyse the associated graviton and light rings that together with the event horizon, provide the necessary components to build its shadow. An analysis of the angular radius of the noncommutative inspired Einstein-Euler-Heisenberg black hole shows that for observers located in its vicinity, it becomes smaller when compared with the commutative case; this effect is more noticeable as noncommutativity increases. The existence of marginally stable bound orbits and the critical angle for the escaping of photons of a noncommutative inspired Einstein-Euler-Heisenberg star is also discussed.

gr-qc↗
arXiv2019

Thermodynamical properties of a noncommutative anti-de Sitter-Einstein-Born-Infeld spacetime from gauge theory of gravity

We construct a deformed adS-Einstein-Born-Infeld black hole from noncommutative gauge theory of gravity and determine the metric coefficients up to second order on the noncommutative parameter. We analyse the modifications on the thermodynamical properties of the black hole due to the noncommutative contributions, and we show that noncommutativity has as a direct consequence, the removal of critical points.

hep-th↗
arXiv2019

A Kähler Compatible Moyal Deformation of the First Heavenly Equation

We construct a noncommutative Kähler manifold based on a non-linear perturbations of Moyal integrable deformations of $D=4$ self-dual gravity. The deformed Kähler manifold preserves all the properties of the commutative one, and we obtain the associated noncommutative Kähler potential using the Moyal deformed gravity approach. We apply this construction to the Atiyah-Hitchin metric and its Kähler potential, which is useful in the description of interactions among magnetic monopoles at low energies.

math-ph↗
arXiv2019

Perturbative calculation of energy levels for the Dirac equation with generalised momenta

We analyse a modified Dirac equation based on a noncommutative structure in phase space. The noncommutative structure induces generalised momenta and contributions to the energy levels of the standard Dirac equation. Using techniques of perturbation theory, we use this approach to find the lowest order corrections to the energy levels and eigenfunctions for two linear potentials in three dimensions, one with radial dependence and another with a triangular shape along one spatial dimension. We find that the corrections due to the noncommutative contributions may be of the same order as the relativistic ones.

math-ph↗
arXiv2019

Holographic superconductor from a non-commutative inspired anti-de Sitter-Einstein-Born-Infeld black hole

Using a noncommutative inspired anti-de Sitter-Einstein-Born-Infeld black hole with both non-commutative mass and charge distributions, we analyse a holographic superconductor in the context of the AdS/CFT correspondence. We show that the coupling of the Born-Infeld parameter and the noncommutative perturbations provides an enhancing mechanism for higher values of the expectation value of the condensate and that noncommutativity counter-balances nonlinearity of the electrodynamics to keep the ratio $ω_g/T_c \approx 8$.

hep-th↗
arXiv2018

On slowly rotating black holes and nonlinear electrodynamics

We discuss the solution to Einstein's equations for a Lense-Thirring inspired metric describing a slowly rotating black hole coupled to nonlinear electrodynamics. We show that different schemes of rotation for the black hole exist; they depend on a parameter $γ$ defining the dependence of the metric on the polar angle. The fulfilment of the complete set of gravitational field equations and conservation laws implies constraints on this parameter and the metric functions. The vanishing of $γ$ provides the Lense-Thirring line element associated to any non-linear electrodynamics; the Kerr-Newman metric for slow rotation arises when $γ$ is not vanishing, a feature that emphasises the unique role played by Maxwell's electrodynamics.

gr-qc↗
arXiv2018

Non-commutative inspired black holes in Euler-Heisenberg non-linear electrodynamics

We find non-commutative inspired electrically and magnetically charged black hole solutions in Euler-Heisenberg non-linear electrodynamics. For these solutions, we determine the non-commutative corrections to the horizon radius for the general and extremal case. We also analyse the weak, dominant and strong energy conditions and the shadow associated with these metrics.

gr-qc↗
arXiv2016

Noncommutative Dirac quantization condition using the Seiberg-Witten map

We investigate the validity of the Dirac quantization condition (DQC) for magnetic monopoles in noncommutative space-time. We use an approach based on an extension of the method introduced by Wu and Yang; the effects of noncommutativity are analyzed using the Seiberg-Witten map and the corresponding deformed Maxwell's equations are discussed. By means of a perturbation expansion in the noncommutativity parameter $θ$, we show first that the DQC remains unmodified up to the first and second order. This result is then generalized to all orders in the expansion parameter for a class of noncommutative electric currents induced by the Seiberg-Witten map; these currents reduce to the Dirac delta function in the commutative limit.

hep-th↗
arXiv2014

Test Particle Motion in the Born-Infeld Black Hole

In this work we review the classification of geodesics of massive test particles in the gravitational background of the black hole solutions of Einstein-Born-Infeld spacetime. Even though some features are quite similar to those of Reissner-Nordström spacetime there are also important differences, particularly those related to the effective potential governing the geodesic motion. Explicit solutions involving Weierstrass functions are given for a pair of specific scenarios.

gr-qc↗
arXiv2014

Non-commutative Einstein-Proca Space-time

In this work we present a deformed model of Einstein-Proca space-time based on the replacement of point-like sources by non-commutative smeared distributions. We discuss the solutions to the set of non-commutative Einstein-Proca equations thus obtained, with emphasis on the issue of singularities and horizons.

hep-th↗
arXiv2013

Exact BPS bound for noncommutative baby Skyrmions

The noncommutative baby Skyrme model is a Moyal deformation of the two-dimensional sigma model plus a Skyrme term, with a group-valued or Grassmannian target. Exact abelian solitonic solutions have been identified analytically in this model, with a singular commutative limit. Inside any given Grassmannian, we establish a BPS bound for the energy functional, which is saturated by these baby Skyrmions. This asserts their stability for unit charge, as we also test in second-order perturbation theory.

hep-th↗
arXiv2010

The Noncommutative Ward Metric

We analyze the moduli-space metric in the static non-Abelian charge-two sector of the Moyal-deformed CP^1 sigma model in 1+2 dimensions. After carefully reviewing the commutative results of Ward and Ruback, the noncommutative K"ahler potential is expanded in powers of dimensionless moduli. In two special cases we sum the perturbative series to analytic expressions. For any nonzero value of the noncommutativity parameter, the logarithmic singularity of the commutative metric is expelled from the origin of the moduli space and possibly altogether.

hep-th↗
arXiv2006

On the Birman-Schwinger principle applied to (-Delta + m^2)^(1/2) - m

The condition for E = 0 to be an eigenvalue of the operator (-Delta + m^2)^(1/2) -m + l V is obtained through the use of the Birman-Schwinger principle. By setting E=-a^2 and using the analyticity of the corresponding Birman-Schwinger kernel, the series development of (l^(-1))(a) is obtained up to second order on a.

math-ph↗