140 research outputs found
Electro and magneto statics of topological insulators as modeled by planar, spherical and cylindrical boundaries: Green function approach
The Green function (GF) method is used to analyze the boundary effects
produced by a Chern Simons (CS) extension to electrodynamics. We consider the
electromagnetic field coupled to a term that is piecewise constant in
different regions of space, separated by a common interface , the
boundary, model which we will refer to as electrodynamics
( ED). This model provides a correct low energy effective action for
describing topological insulators (TI). In this work we construct the static GF
in ED for different geometrical configurations of the
boundary, namely: planar, spherical and cylindrical interfaces. Also
we adapt the standard Green theorem to include the effects of the
boundary. These are the most important results of our work, since they allow to
obtain the corresponding static electric and magnetic fields for arbitrary
sources and arbitrary boundary conditions in the given geometries. Also, the
method provides a well defined starting point for either analytical or
numerical approximations in the cases where the exact analytical calculations
are not possible. Explicit solutions for simple cases in each of the
aforementioned geometries for boundaries are provided. The adapted
Green theorem is illustrated by studying the problem of a point like electric
charge interacting with a planar TI with prescribed boundary conditions. Our
generalization, when particularized to specific cases, is successfully compared
with previously reported results, most of which have been obtained by using the
methods of images.Comment: 24 pages, 4 figures, accepted for publication in PRD. arXiv admin
note: text overlap with arXiv:1511.0117
Structural aspects of Lorentz-violating quantum field theory
In the last couple of decades the Standard Model Extension has emerged as a fruitful framework to analyze the empirical and theoretical extent of the validity of cornerstones of modern particle physics, namely, of Special Relativity and of the discrete symmetries C, P and T (or some combinations of these). The Standard Model Extension allows to contrast high-precision experimental tests with posited alterations representing minute Lorentz and/or CPT violations. To date no violation of these symmetry principles has been observed in experiments, mostly prompted by the Standard-Model Extension. From the latter, bounds on the extent of departures from Lorentz and CPT symmetries can be obtained with ever increasing accuracy. These analyses have been mostly focused on tree-level processes. In this presentation I would like to comment on structural aspects of perturbative Lorentz violating quantum field theory. I will show that some insight coming from radiative corrections demands a careful reassessment of perturbation theory. Specifically I will argue that both the standard renormalization procedure as well as the Lehmann-Symanzik-Zimmermann reduction formalism need to be adapted given that the asymptotic single-particle states can receive quantum corrections from Lorentz-violating operators that are not present in the original Lagrangian.Universidad Andres Bello
DI-27-11/R
DI-33-17/RG
AAEC 2017/2
FONDECYT - 11121633info:eu-repo/semantics/publishedVersio
Green's function approach to Chern-Simons extended electrodynamics: an effective theory describing topological insulators
Boundary effects produced by a Chern-Simons (CS) extension to electrodynamics
are analyzed exploiting the Green's function (GF) method. We consider the
electromagnetic field coupled to a -term in a way that has been
proposed to provide the correct low energy effective action for topological
insulators (TI). We take the -term to be piecewise constant in
different regions of space separated by a common interface , to be
called the -boundary. Features arising due to the presence of the
boundary, such as magnetoelectric effects, are already known in CS extended
electrodynamics and solutions for some experimental setups have been found with
specific configuration of sources. In this work we illustrate a method to
construct the GF that allows to solve the CS modified field equations for a
given -boundary with otherwise arbitrary configuration of sources. The
method is illustrated by solving the case of a planar -boundary but can
also be applied for cylindrical and spherical geometries for which the
-boundary can be characterized by a surface where a given coordinate
remains constant. The static fields of a point-like charge interacting with a
planar TI, as described by a planar discontinuity in , are calculated
and successfully compared with previously reported results. We also compute the
force between the charge and the -boundary by two different methods,
using the energy momentum tensor approach and the interaction energy calculated
via the GF. The infinitely straight current-carrying wire is also analyzed
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 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 corrections to the metric,
for an arbitrary zeroth-order embedding parameter. In particular, the slowly
rotating Kerr metric is an solution in either the
canonical or the axial embeddings.Comment: 5 pages, PRD accepte
Massive photons and Lorentz violation
All quadratic translation- and gauge-invariant photon operators for Lorentz
breakdown are included into the Stueckelberg Lagrangian for massive photons in
a generalized \xi-gauge. The corresponding dispersion relation and tree-level
propagator are determined exactly, and some leading-order results are derived.
The question of how to include such Lorentz-violating effects into a
perturbative quantum-field expansion is addressed. Applications of these
results within Lorentz-breaking quantum field theories include the
regularization of infrared divergences as well as the free propagation of
massive vector bosons.Comment: 12 pages, 1 figur
Electromagnetic fields induced by an electric charge near a Weyl semimetal
[EN] Weyl semimetals (WSM) are a new class of topological materials that exhibit a bulk Hall effect and a chiral magnetic effect. The topological contribution of these unusual electromagnetic responses can be characterized by an axion term θE·B with space and time dependent axion angle θ(r,t). In this paper we compute the electromagnetic fields produced by an electric charge near a topological Weyl semimetal with two Weyl nodes, in the equilibrium state, at zero electric chemical potential, and with broken time-reversal symmetry. We find that, as in ordinary metals and dielectrics, outside the WSM the electric field is mainly determined by the optical properties of the material. The magnetic field is, on the contrary, of topological origin due to the magnetoelectric effect of topological phases. We show that the magnetic field exhibits an interesting behavior above the WSM as compared with that induced above a topological insulator: the field lines begin at the surface and then end at the surface (but not at the same point). This distinctive behavior of the magnetic field is an experimentally observable signature of the anomalous Hall effect in the bulk of the WSM. We discuss two experimental setups for testing our predictions of the induced magnetic field.We thank Alberto Cortijo for useful comments and suggestions, and also to the anonymous referees for their recommendations. A.M. was supported by the CONACyT postdoctoral
Grant No. 234774. L.F.U. has been supported in part by the project CONACyT (MĂ©xico) No. 237503. M.C. has been partially supported by UNAB DGID under Grant No. DI-33-17/RG and wishes to thank A. MartĂn-Ruiz and L. F. Urrutia at Instituto de Ciencias Nucleares, UNAM for the kind hospitality of throughout the preparation of the manuscript
Bare and Induced Lorentz and CPT Invariance Violations in QED
We consider QED in a constant axial vector background (\AE ther). Further
Lorentz invariance violations (LIV) might occur owing to radiative corrections.
The phenomenology of this model is studied, clarifying issues related to the
various regularizations employed, with a particular emphasis on the induced
photon mass. To this concern, it is shown that in the presence of LIV
dimensional regularization may produce a radiatively induced finite photon
mass. The possible physical role of the large momentum cutoff is elucidated and
the finite temperature radiative corrections are evaluated. Finally, various
experimental bounds on the parameters of the model are discussed.Comment: latex, 29 page
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