arXiv subjects

E. Goulart

Publications and source records attributed to E. Goulart.

16 recordsLinked to original sources

arXiv2025

Propagation features of Lorentz-violating electrodynamics

This paper explores some propagation features of electrodynamics in a Lorentz-violating scenario, focusing on a specific CPT-even term within the photon sector of the Standard Model Extension (SME). The study derives a covariant dispersion relation for light propagation in the presence of a Lorentz-violating symmetric tensor field $C_{ab}(x)$, which reveals a modified light cone structure described by a quartic polynomial. The analysis includes a simplified model where the tensor field assumes a dyadic form, leading to an effective metric that dictates the propagation. The paper investigates three distinct cases: Lorentz-violating vectors which are timelike, lightlike and spacelike, and examines their implications for the effective velocity of light, birefringence, and analogies with electrodynamics in material media. The results highlight anisotropic propagation effects and provide insights into the interplay between Lorentz violation and modified causal structures. The study concludes with a discussion of the phenomenological implications and possible experimental tests for such Lorentz-violating effects.

hep-th↗

arXiv2023

Remarks on the algebraic structure of (2, 2) double forms

We study the algebraic features of covariant tensors of valence four containing two blocks of skew indices. After a rather general treatment, we specialize ourselves to four-dimensional spacetimes and discuss several complementary aspects of these objects. In particular, we focus our attention on the corresponding invariant subspaces and generalise previous relations such as the Ruse-Lanczos identity, the Bel-Matte decomposition and the Lovelock-like quadratic identities. We conclude pointing out some possible applications of the formalism.

gr-qc↗

arXiv2020

Towards a unified description of knotted light

Several complementary approaches to investigate knotted solutions of Maxwell's equations in vacuum are now available in literature. However, only partial results towards a unified description of them have been achieved. This is potentially worrying, since new developments of the theory possibly lie at the intersection between the appropriate formalisms. The aim of this paper is to pave the way for a theoretical framework in which this unification becomes feasible, in principle.

math-ph↗

arXiv2018

On spacetime foliations and electromagnetic knots

The present paper has a number of distinct purposes. First is to give a description of a class of electromagnetic knots from the perspective of foliation theory. Knotted solutions are then interpreted in terms of two codimension-2 foliations whose knotted leaves intersect orthogonally everywhere in spacetime. Secondly, we show how the foliations give rise to field lines and how the topological invariants emerge. The machinery used here emphasizes intrinsic properties of the leaves instead of observer dependent quantities - such as a time function, a local rest frame or a Cauchy hypersurface. Finally, we discuss the celebrated Hopf-Rañada solution in details and stress how the foliation approach may help in future developments of the theory of electromagnetic knots. We conclude with several possible applications, extensions and generalizations.

math-ph↗

arXiv2016

Nonlinear electrodynamics is skilled with knots

The aims of this letter are three-fold: First is to show that nonlinear generalizations of electrodynamics support various types of knotted solutions in vacuum. The solutions are universal in the sense that they do not depend on the specific Lagrangian density, at least if the latter gives rise to a well-posed theory. Second is to describe the interaction between probe waves and knotted background configurations. We show that the qualitative behaviour of this interaction may be described in terms of Robinson congruences, which appear explicitly in the causal structure of the theory. Finally, we argue that optical arrangements endowed with intense background fields could be the natural place to look for the knots experimentally.

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arXiv2015

Characteristic analysis for integrable soliton models on two-dimensional target spaces

We investigate the evolutionary aspects of some integrable soliton models whose Lagrangians are derived from the pullback of a volume-form to a two-dimensional target space. These models are known to have infinitely many conserved quantities and support various types of exact analytic solutions with nontrivial topology. In particular, we show that, in spite of the fact that they admit nice smooth solutions, wave propagation about these solutions will always be ill-posed. This is related to the fact that the corresponding Euler-Lagrange equations are not of hyperbolic type.

math-ph↗

arXiv2013

Disformal invariance of Maxwell's field equations

We show that Maxwell's electrodynamics in vacuum is invariant under active transformations of the metric. These metrics are related by disformal mappings induced by derivatives of the gauge vector $A_μ$ such that the gauge symmetry is preserved. Our results generalize the well known conformal invariance of electrodynamics and characterize a new type of internal symmetry of the theory. The group structure associated with these transformations is also investigated in details.

gr-qc↗

arXiv2013

Geometric scalar theory of gravity

We present a geometric scalar theory of gravity. Our proposal will be described using the "background field method" introduced by Gupta, Feynman and others as a field theory formulation of general relativity. We analyze previous criticisms against scalar gravity and show how the present proposal avoids these difficulties. This concerns not only the theoretical complaints but also those related to observations. In particular, we show that the widespread belief of the conjecture that the source of scalar gravity must be the trace of the energy-momentum tensor - which is one of the main difficulties to couple gravity with electromagnetic phenomenon in previous models - does not apply to our geometric scalar theory. Some consequences of the new scalar theory are explored.

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arXiv2011

A new symmetry of the relativistic wave equation

In this paper we show that there exists a new symmetry in the relativistic wave equation for a scalar field in arbitrary dimensions. This symmetry is related to redefinitions of the metric tensor which implement a map between non-equivalent manifolds. It is possible to interpret these transformations as a generalization of the conformal transformations. In addition, one can show that this set of manifolds together with the transformation connecting its metrics forms a group. As long as the scalar field dynamics is invariant under these transformations, there immediately appears an ambiguity concerning the definition of the underlying background geometry.

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arXiv2011

Electromagnetic Geometry

We show that Maxwell's electromagnetism can be mapped into the Born-Infeld theory in a curved space-time, which depends only on the electromagnetic field in a specific way. This map is valid for any value of the two lorentz invariants $F$ and $G$ confirming that we have included all possible solutions of Maxwell's equations. Our result seems to show that specifying the dynamics and the space-time structure of a given theory can be viewed merely as a choice of representation to describe the physical system.

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arXiv2011

Hidden geometries in nonlinear theories: a novel aspect of analogue gravity

We show that non-linear dynamics of a scalar field ϕ may be described as a mod- ification of the spacetime geometry. Thus, the self-interaction is interpreted as a coupling of the scalar field with an effective gravitational metric that is constructed with ϕ itself. We prove that this process is universal, that is, it is valid for arbi- trary Lagrangian. Our results are compared to usual analogue models of gravitation, where the emergence of a metric appears as a consequence of linear perturbation.

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arXiv2011

Effective metric in nonlinear scalar field theories

We discuss several features of the propagation of perturbations in nonlinear scalar field theories using the effective metric. It is shown that the effective metric can be classified according to whether the gradient of the scalar field is timelike, null, or spacelike, and this classification is illustrated with two examples. We shall also show that different signatures for the effective metric are allowed.

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arXiv2011

Beyond Analog Gravity: The Case of Exceptional Dynamics

We show that it is possible to go beyond the simple kinematical aspects of the analog models of gravity. We exhibit the form of the Lagrangian that describes the dynamics of a self-interacting field $ ϕ$ as an interaction between $ ϕ$ and its associated effective metric $ \hat{g}^{μν}.$ In other words the non-linear equation of motion of the field may be interpreted as the gravitational influence on $ ϕ$ by its own effective metric which, in our scheme becomes an active partner of the dynamics of $ ϕ. $

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arXiv2011

Scalar Quantum Field Theory in Disordered Media

A free massive scalar field in inhomogeneous random media is investigated. The coefficients of the Klein-Gordon equation are taken to be random functions of the spatial coordinates. The case of an annealed-like disordered medium, modeled by centered stationary and Gaussian processes, is analyzed. After performing the averages over the random functions, we obtain the two-point causal Green's function of the model up to one-loop. The disordered scalar quantum field theory becomes qualitatively similar to a $λϕ^{4}$ self-interacting theory with a frequency-dependent coupling.

hep-th↗

arXiv2008

Formal analogies between gravitation and electrodynamics

We develop a theoretical framework that allows us to compare electromagnetism and gravitation in a fully covariant way. This new scenario does not rely on any kind of approximation nor associate objects with different operational meaning as it's sometime done in the literature. We construct the electromagnetic analogue to the Riemann and Weyl tensors and develop the equations of motion for these objects. In particular, we are able to identify precisely how and in what conditions gravity can be mapped to electrodynamics. As a consequence, many of the gemometrical tools of General Relativity can be applied to Electromagnetism and vice-versa. We hope our results would shed new light in the nature of electromagnetic and gravitational theories.

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arXiv2006

Cosmological Effects of Nonlinear Electrodynamics

It will be shown that a given realization of nonlinear electrodynamics, used as source of Einstein's equations, generates a cosmological model with interesting features, namely a phase of current cosmic acceleration, and the absence of an initial singularity, thus pointing to a way to solve two important problems in cosmology.

gr-qc↗