arXiv subjects

Luis F. Urrutia

Publications and source records attributed to Luis F. Urrutia.

At least 19 recordsLinked to original sources

arXiv2026

Exact modes, hybridization and polarization rotation of electromagnetic fields propagating in topological insulating slab

We study electromagnetic waves in slab waveguides with a topological insulator core characterized by a topological magnetoelectric parameter (ME). TIs are electrically insulating in the bulk with robust conducting states at their boundaries. Their electromagnetic response is described by an axion-like $Θ$ term that modifies Maxwell's electrodynamics, leading to rich and unconventional phenomena, as the topological ME effect. All supported modes are exact hybrid modes with nonvanishing longitudinal field components. This hybridization is a consequence of the boundary conditions produced by the $Θ$ term and is absent in topologically trivial, reciprocal and non-chiral slab waveguides. Modifications to the propagation condition and modes are shown for the asymmetric slab. The detailed solution of the exact modes, coupling of modes and the dispersion relations is made for the symmetric slab. By solving the full $Θ$-electrodynamics nonperturbatively, we derive the modal dispersion relations and explore polarization rotation and power transfer between modes. Our approach reveals qualitative and quantitative deviations from standard coupled-mode theory and captures new signatures of the topological ME response. Due to the smallness of the $Θ$-effects, we perform a perturbative analysis of mode propagation, based on writing a general solution as a superposition of exact modes of $Θ$-ED but expanding to first non-vanishing order. Also, we apply coupled-mode theory, that is predicated on building solutions as superpositions of modes of ordinary electrodynamics that fail to satisfy the boundary conditions imposed by the $Θ$-term but compensate at the expense of modifying the field profiles. These findings provide a comprehensive framework for light control in topological photonics and potential routes to experimentally probe the ME effect in guided settings.

physics.optics↗

arXiv2026

Revisiting Cherenkov radiation in anisotropic chiral matter: exact calculation reveals threshold-free emission

We explore Cherenkov radiation in anisotropic chiral matter within the framework of Carroll-Field-Jackiw electrodynamics, where the axion angle exhibits a linear dependence on position. By deriving closed-form expressions for the polarization modes of electromagnetic fields in cylindrical coordinates and the space-frequency domain, we solve the modified Maxwell's equations. To enforce causality, we impose outgoing wave boundary conditions at a cylindrical surface at infinity, which yields the dispersion relations. Our analysis uncovers the specific angles and frequency ranges that allow for zero, one, or two Cherenkov cones. We also obtain the spectral energy distribution of the radiation in all cases. Notably, one sector of the model exhibits a novel phenomenon: Cherenkov radiation can be generated by slowly moving charges without a threshold, but only within a specific frequency range. This behavior is not observed in standard materials. Using our exact calculations, we also investigate the reliability of an approximate method previously proposed based on the calculation of the Green's function for the system.

hep-ph↗

arXiv2026

Anomalous Hall effect in anisotropic type-II Weyl semimetals

We extend our previous analysis [Phys. Rev. D 109, 065005 (2024)] of CPT-odd electromagnetic response in tilted, anisotropic Weyl semimetals to the overtilted (type-II) regime, where electron and hole pockets coexist at the Fermi level. Starting from the minimal QED sector of the Standard-Model Extension matched to a lattice-motivated anisotropic Dirac Hamiltonian with tilt, we compute the zero-temperature finite-density effective action nonperturbatively from the vacuum polarization tensor, and corroborate the result using a complementary chiral kinetic theory formulation that consistently incorporates both Fermi-sea and Fermi-surface contributions. In the type-II regime the unbounded linear dispersion necessitates a physical ultraviolet regularization. Implementing a hard momentum cutoff tied to the lattice bandwidth, we show that the CPT-odd, axion-like response remains finite across the type-I to type-II Lifshitz transition, while acquiring tilt- and anisotropy-dependent renormalizations together with nonuniversal, cutoff-sensitive terms governed by the geometry of the electron and hole pockets. As a concrete application, we evaluate the anomalous Hall conductivity in the prototypical type-II Weyl semimetal WTe$_2$, using parameters extracted from first-principles calculations and experiments, and find that Fermi-sea and Fermi-surface contributions are comparable and partially cancel, yielding a finite and strongly anisotropic Hall response characteristic of the overtilted regime.

hep-th↗

arXiv2025

Cherenkov radiation in isotropic chiral matter: the space-frequency domain

The electromagnetic response of isotropic chiral matter, as described by Carroll-Field-Jackiw electrodynamics, arises in distinct physical contexts ranging from condensed matter systems to Lorentz-violating extensions of high-energy physics. Here, we derive exact expressions for the circularly polarized electromagnetic fields that contribute independently to Cherenkov radiation in isotropic chiral matter. Each spectral energy distribution is gauge-invariant and positive, yielding radiation that emerges at a characteristic angle, akin to the standard case. Furthermore, we identify specific frequency ranges that permit zero, one, or two Cherenkov cones for a given setup. Remarkably, one sector of the model allows for the existence of threshold-free Cherenkov radiation arising from slowly-moving charges.

hep-ph↗

arXiv2025

Effective electromagnetic Lagrangians in the derivative expansion method

We calculate the effective electromagnetic Lagrangian up to the lowest-order corrections in the derivatives for two fermionic systems of interest in condensed matter physics in the linearized approximation of the tight-binding Hamiltonian near the Fermi level in the Brillouin zone: (i) the $(3+1)$ description of the simplest Weyl semimetal and (ii) the massive $(2+1)$ electrodynamics, which can serve as a model for the interface between two $(3+1)$ topological insulators. We employ the derivative expansion method which directly provides local effective Lagrangians and allows selecting from the outset both the powers of the electromagnetic potential to be considered together with the number of relevant derivatives. We find new higher-order derivative corrections to Carroll-Field-Jackiw electrodynamics. In general, the new terms we find either have a similar structure or constitute a relativistic generalization of some recent phenomenological proposals found in the literature. In this way, they should be incorporated into these proposals for assessing the relative significance of all the terms included up to a given order.

hep-th↗

arXiv2025

Split Cherenkov radiation in isotropic chiral matter

Chiral matter exhibits unique electromagnetic responses due to the macroscopic manifestation of the chiral anomaly as anomalous transport currents. Here, we study the modification of electromagnetic radiation in isotropic chiral matter characterized by an axion coupling that varies linearly over time $θ(t) = b_0 t$. Using Carroll-Field-Jackiw electrodynamics, we derive the causal Green's function to investigate the stability and radiation properties of the system. Even though the plane-wave modes of isotropic chiral matter exhibit imaginary frequencies for long wavelengths, which might suggest instability in the system, we show that their contribution is confined to the near-field region. Also we find no exponentially growing fields at arbitrarily large times, so that stability is preserved. Under these conditions the radiation yields a positive energy flux, although this is not an inherent property of the general definition. In the case of a fast-moving charge, we confirm the existence of vacuum Cherenkov radiation and show that, for refractive indices $n > 1$, the Cherenkov cone can split into two concentric cones with opposite circular polarizations. This split, governed by the speed of the particle $v$, $n$ and $b_0$, resembles the optical spin-Hall effect and offers potential applications for creating circularly polarized terahertz (THz) light sources. Our Green's function approach provides a general method for analyzing radiation in chiral matter, from Weyl semimetals to quark-gluon plasmas, and can be extended to systems such as oscillating dipoles and accelerated charges.

hep-ph↗

arXiv2024

Momentum non-conservation in a scalar quantum field theory with a planar $θ$ interface

Motivated by the recent interest aroused by non-dynamical axionic electrodynamics in the context of topological insulators and Weyl semimetals, we discuss a simple model of the magnetoelectric effect in terms of a $θ$-scalar field that interacts through a delta-like potential located at a planar interface. Thus, in the bulk regions the field is constructed by standard free waves with the absence of evanescent components. These waves have to be combined into linear superposition to account for the boundary conditions at the interface in order to yield the corresponding normal modes. Our aim is twofold: first we quantize the $θ$-scalar field using the normal modes in the canonical approach and then we look for applications emphasizing the effect of momentum non-conservation due to the presence of the interface. To this end we calculate the decay of a standard scalar particle into two $θ$-scalar particles showing the opening of new decay channels. As a second application we deal with the two body scattering of standard charged scalar particles mediated by a $θ$-scalar particle, focusing on the momentum non-conserving contribution of the scattering amplitude ${\cal M}^{NC}$. We define a generalization of the usual cross section in order to quantify the emergence of these events. We also study the allowed kinematical region for momentum non-conservation as well as the position of the poles of the amplitude ${\cal M}^{NC}$. Finally, the ratio of the magnitudes between ${\cal M}^{NC}$ and the momentum conserving amplitude is discussed in the appropriate region of momentum space.

hep-th↗

arXiv2024

Lorentz invariance violation and the CPT-odd electromagnetic response of a tilted anisotropic Weyl semimetal

We derive the electromagnetic response of a particular fermionic sector in the minimal QED contribution to the Standard Model Extension (SME), which can be physically realized in terms of a model describing a tilted and anisotropic Weyl semimetal (WSM). The contact is made through the identification of the Dirac-like Hamiltonian resulting from the SME with that corresponding to the WSM in the linearized tight-binding approximation. We first calculate the effective action by computing the non-perturbative vacuum polarization tensor using thermal field theory techniques, focusing upon the corrections at finite chemical potential and zero temperature. Next, we confirm our results by a direct calculation of the anomalous Hall current within a chiral kinetic theory approach. In an ideal Dirac cone picture of the WSM (isotropic and non-tilted) such response is known to be governed by axion electrodynamics, with the space-time dependent axion angle $Θ(\mathbf{r},t) = 2 (\mathbf{b} \cdot \mathbf{r} - b _{0} t)$, being $2 \mathbf{b}$ and $2b _{0}$ the separation of the Weyl nodes in momentum and energy, respectively. In this paper we demonstrate that the node tilting and the anisotropies induce novel corrections at a finite density which however preserve the structure of the axionic field theory. We apply our results to the ideal Weyl semimetal $\mathrm{EuCd}_{2}\mathrm{As}_{2}$ and to the highly anisotropic and tilted monopnictide $\mathrm{TaAs}$.

hep-th↗

arXiv2023

Electromagnetic Radiation in chiral matter: the Cherenkov case

Starting from the modified Maxwell equations in Carroll-Field-Jackiw electrodynamics we study the electromagnetic radiation in a chiral medium characterized by an axion coupling $θ(x)=b_μx^μ$, with $b_μ= (0,\mathbf{b})$, which gives rise to the magnetoelectric effect. Employing the stationary phase approximation we construct the Green's matrix in the radiation zone which allows the calculation of the corresponding electromagnetic potentials and fields for arbitrary sources. We obtain a general expression for the angular distribution of the radiated energy per unit frequency. As an application we consider a charge moving at constant velocity parallel to $\mathbf{b}$ in the medium and discuss the resulting Cherenkov radiation. We recover the vacuum Cherenkov radiation. For the case of a material with refraction index $n > 1$ we find that zero, one or two Cherenkov cones can appear. The spectral distribution of the radiation together with the comparison of the radiation output of each cone are presented, as well as some angular plots showing the appearance of the cones.

hep-ph↗

arXiv2022

Radiation from a dipole perpendicular to the interface between two planar semi-infinite magnetoelectric media

We consider two semi-infinite magnetoelectric media with constant dielectric permittivity separated by a planar interface, whose electromagnetic response is described by non-dynamical axion electrodynamics and investigate the radiation of a point-like electric dipole located perpendicularly to the interface. We start from the exact Green's function for the electromagnetic potential, whose far-field approximation is obtained using a modified steepest descent approximation. This procedure yields the standard spherical waves as well as axially symmetric cylindrical superficial waves, which nevertheless are restricted to a region very close to the interface. We compute the angular distribution of the radiation and the total radiated power finding different interference patterns, depending on the relative position dipole-observer, and polarization mixing effects which are all absent in the standard dipole radiation. They are a manifestation of the magnetoelectric effect induced by axion electrodynamics. We illustrate our findings with some numerical estimations employing realistic media as well as some hypothetical choices in order to illuminate the effects of the magnetoelectric coupling which is usually very small.

cond-mat.other↗

arXiv2020

Magnetic-conductivity effects on electromagnetic propagation in dispersive matter

The Chiral Magnetic Effect (CME) has been investigated as a new transport phenomenon in condensed matter. Such an effect appears in systems with chiral fermions and involves an electric current generated by a magnetic field by means of an "exotic" magnetic conductivity. This effect can also be connected with extensions of the usual Ohm's law either in magnetohydrodynamics or in Lorentz-violating scenarios. In this work, we study the classical propagation of electromagnetic waves in isotropic dispersive matter subject to a generalized Ohm's law. The latter involves currents linear in the magnetic field and implies scenarios inducing parity violation. We pay special attention to the case of a vanishing electric conductivity. For a diagonal magnetic conductivity, which includes the CME, the refractive index is modified such that it implies birefringence. For a nondiagonal magnetic conductivity, modified refractive indices exhibiting imaginary parts occur ascribing a conducting behavior to a usual dielectric medium. Our findings provide new insight into typical material properties associated with a magnetic conductivity.

hep-th↗

arXiv2016

Electromagnetic description of three-dimensional time-reversal invariant ponderable topological insulators

A general technique to analyze the classical interaction between ideal topological insulators, and electromagnetic sources and fields, has been previously elaborated. Nevertheless it is not immediately applicable in the laboratory as it fails to describe real ponderable media. In this work we provide a description of real topologically insulating materials taking into account their dielectric and magnetic properties. For inhomogeneous permittivity and permeability, the problem of finding the Green's function must be solved in an ad hoc manner. Nevertheless, the physically feasible cases of piecewise constant $\varepsilon, μ$ and $θ$ make the problem tractable, where $θ$ encodes the topological magnetoelectric polarizability properties of the medium. To this end we employ the Green's function method to find the fields resulting form the interaction between these materials and electromagnetic sources. Furthermore we exploit the fact that in the cases here studied, the full Green's function can be successfully found if the Green's function of the corresponding ponderable media with $θ= 0$ is known. Our results, satisfactorily reproduce previously existing ones and also generalize some others. The method here elaborated can be exploited to determine the electromagnetic fields for more general configurations aiming to measure the interaction between real 3D topological insulators and electromagnetic fields.

cond-mat.str-el↗

arXiv2016

Lorentz-Invariance Violation with Higher-Order Operators

In this work, in the light of the developments for indefinite metric theories made by Lee and Wick, we study perturbative unitarity in a Lorentz-invariance violating QED model with higher-order operators. We show that by following the Lee-Wick prescription it is possible to preserve unitarity in the model at one-loop order in the coupling.

hep-ph↗

arXiv2010

An extended solution space for Chern-Simons gravity: the slowly rotating Kerr black hole

In the Einstein-Cartan formulation, an iterative procedure to find solutions in non-dynamical Chern-Simons (CS) gravity in vacuum is proposed. The iterations, in powers of a small parameter $β$ which codifies the CS coupling, start from an arbitrary torsionless solution of Einstein equations. With Schwarzschild as the zeroth-order choice, we derive a second-order differential equation for the $\mathcal{O}(β)$ corrections to the metric, for an arbitrary zeroth-order embedding parameter. In particular, the slowly rotating Kerr metric is an $\mathcal{O}(β)$ solution in either the canonical or the axial embeddings.

gr-qc↗

arXiv2010

Slowly rotating Kerr black hole as a solution of Einstein-Cartan gravity extended by a Chern-Simons term

We consider the nondynamical Chern-Simons (CS) modification to General Relativity (GR) in the framework of the Einstein-Cartan formulation, as providing a way to incorporate a slowly rotating Kerr black hole in the space of solutions. Our proposal lies on considering the CS term as a source of torsion and on an iterative procedure to look for vacuum solutions of the system, by expanding the tetrad, the connection and the embedding parameter, in powers of a dimensionless small parameter $β$ which codifies the CS coupling. Starting from a torsionless zeroth-order vacuum solution we derive the second-order differential equation for the $\mathcal{O}(β)$ corrections to the metric, for an arbitrary embedding parameter. Furthermore we can show that the slowly rotating Kerr metric is an $\mathcal{O}(β)$ solution of the system either in the canonical or the axial embeddings.

gr-qc↗

arXiv2009

Gauge invariant non-linear electrodynamics motivated by a spontaneous breaking of the Lorentz symmetry

We introduce a new version of non-linear electrodynamics which is produced by a spontaneous symmetry breaking of Lorentz invariance induced by the non-zero expectation value of the electromagnetic field strength. The symmetry breaking potential is argued to effectively arise from the integration of massive gauge bosons and fermions in an underlying fundamental theory. All possible choices of the vacuum lead only to the remaining invariant subgroups T(2) and HOM(2). We explore the plane wave solutions of the linearized sector of the model for an arbitrary vacuum. They present two types of dispersion relations. One corresponds to the case of the usual Maxwell electrodynamics with the standard polarization properties of the fields. The other dispersion relation involves anisotropies determined by the structure of the vacuum. The model is stable in the small Lorentz invariance violation approximation. We have embedded our model in the photon sector of the Standard Model Extension in order to set bounds for our parameters. The one-way anisotropic speed of light is calculated for a general vacuum and its isotropic component is strongly bounded by ${\tilde δc}/c < 2 \times 10^{-32}$. The anisotropic violation contribution is estimated by introducing an alternative definition for the difference of the two-way speed of light in perpendicular directions $Δc$, which is also strongly bounded by ${Δc}/c < 10^{-32}$. Finally, we speculate on the relation of the vacuum energy of the model with the cosmological constant and propose a connection between the vacuum fields and the intergalactic magnetic fields.

hep-ph↗

arXiv2008

Dimensional reduction as a method to obtain dual theories for massive spin two in arbitray dimensions

Using the parent Lagrangian method together with a dimensional reduction from $D$ to $(D-1)$ dimensions we construct dual theories for massive spin two fields in arbitrary dimensions in terms of a mixed symmetry tensor $T_{A[A_{1}A_{2}... A_{D-2}]}$. Our starting point is the well studied massless parent action in dimension $D$. The resulting massive Stueckelberg-like parent actions in $(D-1)$ dimensions inherits all the gauge symmetries of the original massless action and can be gauge fixed in two alternative ways, yielding the possibility of having either a parent action with a symmetric or a non-symmetric Fierz-Pauli field $e_{AB}$. Even though the dual sector in terms of the standard spin two field includes only the symmetrical part $e_{\{AB\}}$ in both cases, these two possibilities yield different results in terms of the alternative dual field $T_{A[A_{1}A_{2}... A_{D-2}]}$. In particular, the non-symmetric case reproduces the Freund-Curtright action as the dual to the massive spin two field action in four dimensions.

hep-th↗

arXiv2008

Coping with the Pais-Uhlenbeck oscillator's ghosts in a canonical approach

A {\em complex} canonical transformation is found that takes the fourth order derivative Pais-Uhlenbeck oscillator into two independent harmonic oscillators thus showing that this model has energy bounded from below, unitary time-evolution and no negative norm states, or ghosts. Such transformation yields a positive definite inner product consistent with reality conditions in the Hilbert space. The method is illustrated by eliminating the negative norm states in a complex oscillator. Extensions to other higher order mechanical models and field theory are discussed.

quant-ph↗