Lorentz Symmetry Violation Research Articles

Lorentz-violating effects in three-dimensional QED

Inspired in discussions presented lately regarding Lorentz-violating interaction terms in B. Charneski, M. Gomes, R. V. Maluf and A. J. da Silva, Phys. Rev. D86, 045003 (2012); R. Casana, M. M. Ferreira Jr., R. V. Maluf and F. E. P. dos Santos, Phys. Lett. B726, 815 (2013); R. Casana, M. M. Ferreira Jr., E. Passos, F. E. P. dos Santos and E. O. Silva, Phys. Rev. D87, 047701 (2013), we propose here a slightly different version for the coupling term. We will consider a modified quantum electrodynamics with violation of Lorentz symmetry defined in a (2+1)-dimensional space–time. We define the Lagrangian density with a Lorentz-violating interaction, where the space–time dimensionality is explicitly taken into account in its definition. The work encompasses an analysis of this model at both zero and finite-temperature, where very interesting features are known to occur due to the space–time dimensionality. With that in mind, we expect that the space–time dimensionality may provide new insights about the radiative generation of higher-derivative terms into the action, implying in a new Lorentz-violating electrodynamics, as well the nonminimal coupling may provide interesting implications on the thermodynamical quantities.

Scalar Aharonov‐Bohm‐type effect induced by Lorentz symmetry breaking effects

A possible scenario of the Lorentz symmetry violation is discussed based on the arising of geometric quantum phases yielded by the effects of the Lorentz symmetry violation in the CPT‐even gauge sector of Standard Model Extension. Analogues of the Anandan quantum phase and the scalar Aharonov‐Bohm effect for a neutral particle [J. Anandan, Phys. Lett. A 138, 347 (1989)] are obtained from the parity‐odd sector of the tensor . Moreover, we build quantum holonomies associated with the analogue of the Anandan quantum phase and discuss a possible analogy with the geometric quantum computation [A. Ekert et al., J. Mod. Opt. 47, 2501 (2000)]. image

Absence of long-wavelength Cerenkov radiation with isotropic Lorentz andCPTviolation

Modified theories of electrodynamics that include violations of Lorentz symmetry often allow for the possibility of vacuum Cerenkov radiation. This phenomenon has previously been studied in a number of Lorentz-violating theories, but none of the methods that have previously been developed are sufficient to study a theory with a timelike Chern-Simons term ${k}_{AF}$, because such a term may generate exponentially growing solutions to the field equations. Searching for vacuum Cerenkov radiation in a theory with a purely timelike Chern-Simons term using only elementary methods, we find that, despite the presence of the runaway modes, a charge in uniform nonrelativistic motion does not radiate energy, up to second order in the velocity.

On the Lorentz symmetry breaking effects on a Dirac neutral particle inside a two-dimensional quantum ring

We study the effects of the Lorentz symmetry violation in the nonrelativistic quantum dynamics of a spin-1/2 neutral particle interacting with external fields confined to a two-dimensional quantum ring (W.-C. Tan, J.C. Inkson, Semicond. Sci. Technol. 11, 1635 (1996)). We show a possible scenario for the Lorentz symmetry breaking that permits us to make an analogy with the Landau-Aharonov-Casher system (M. Ericsson, E. Sjoqvist, Phys. Rev. A 65, 013607 (2001)), where a change in the angular frequency characteristic of the confinement of a quantum particle to a two-dimensional ring is obtained. Then, we show that an upper bound for the Lorentz symmetry breaking parameters may be set up. Besides, we analyse another possible scenario of the Lorentz symmetry violation by showing the presence of an analogue of the Coulomb potential. We obtain the bound states solutions to the Schrodinger-Pauli equation and discuss a quantum effect characterized by the dependence of the angular frequency on the quantum numbers of the system.

The CTA sensitivity to Lorentz-violating effects on the gamma-ray horizon

The arrival of TeV-energy photons from distant galaxies isexpected to be affected by their QED interaction with intergalactic radiation fieldsthrough electron-positron pair production. In theories where high-energy photons violate Lorentz symmetry,the kinematics of the process γ+γ→e++e− is altered and the cross section suppressed.Consequently, one would expect more of the highest-energy photons to arrive if QED is modified by Lorentz violation than if it is not.We estimate the sensitivity of Cherenkov Telescope Array (CTA) to changes in the gamma-ray horizonof the Universe due to Lorentz violation, and find that it should be competitive with other leading constraints.

Lorentz violation and higher derivative gravity

In this work, we analyze a gravity model with higher derivatives including a $CPT$-even Lorentz-violating term. In principle, the model could be a low-energy limit of a Lorentz-invariant theory presenting the violation of Lorentz symmetry as a consequence of a spontaneous symmetry-breaking mechanism if a decoupling between the metric and the Nambu-Goldstone modes is assumed. We have set up a convenient operator basis for the expansion of wave operators for symmetric second-rank tensors in the presence of a background vector. By using this set of operators, the particle content is obtained, and its consistency, regarding the conditions for stability and unitarity, is discussed. We conclude that this extra Lorentz noninvariant contribution is unable to address the problems of stability and unitarity of higher-derivative gravity models.

Cosmic magnetization in curved and Lorentz violating space–times

The presence of the large-scale magnetic fields is one of the greatest puzzles of contemporary cosmology. The symmetries of the electromagnetic field theory combined with the geometric structure of the FRW universe leads to an adiabatic decay of the primordial magnetic fields. Due to this rapid decay the residual large-scale magnetic field is astrophysically unimportant. A common feature among many of the proposed amplification mechanisms is the violation of Lorentz symmetries. We introduce an amplification mechanism within a Lorentz violating environment where we use Finsler geometry as our theoretical background. The mechanism is based on the adoption of a local anisotropic structure that leads to modifications on the Ricci identities. Thus, the wave-like equation of any vector source, including the magnetic field, is enriched by the Finslerian curvature theory. In particular limits, the remaining seed field can be strong enough to seed the galactic dynamo. In our analysis we also develop the 1+3 covariant formalism for the 4-vector potential in curved space–times.

Strong binary pulsar constraints on Lorentz violation in gravity.

Binary pulsars are excellent laboratories to test the building blocks of Einstein's theory of general relativity. One of these is Lorentz symmetry, which states that physical phenomena appear the same for all inertially moving observers. We study the effect of violations of Lorentz symmetry in the orbital evolution of binary pulsars and find that it induces a much more rapid decay of the binary's orbital period due to the emission of dipolar radiation. The absence of such behavior in recent observations allows us to place the most stringent constraints on Lorentz violation in gravity, thus verifying one of the cornerstones of Einstein's theory much more accurately than any previous gravitational observation.

Unitarity in a Lorentz symmetry breaking model with higher-order operators

We analyze the unitarity of a modified QED with higher-order terms that violate Lorentz symmetry. We make an explicit calculation to verify unitarity at the one-loop level. As expected we find negative norm states that could in principle lead to a violation of unitarity. However, we show that these states become massive in Euclidean space and do not contribute to the discontinuity.

QUANTUM FIELD THEORY WITH VARYING COUPLINGS

A quantum scalar field theory with spacetime-dependent coupling is studied. Surprisingly, while translation invariance is explicitly broken in the classical theory, momentum conservation is recovered at the quantum level for some specific choice of the coupling's profile for any finite-order perturbative expansion. For one of these cases, some tree and one-loop diagrams are calculated. This is an example of a theory where violation of Lorentz symmetry is not enhanced at the quantum level. We draw some consequences for the renormalization properties of certain classes of fractional field theories.

High-energy cosmic rays and tests of basic principles of Physics

With the present understanding of data, the observed flux suppression for ultra-high energy cosmic rays (UHECR) at energies above 4.10E19 eV can be a signature of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or be related to a similar mechanism. But it may also correspond, for instance, to the maximum energies available at the relevant sources. In both cases, violations of special relativity modifying cosmic-ray propagation or acceleration at very high energy can potentially play a role. Other violations of fundamental principles of standard particle physics (quantum mechanics, energy and momentum conservation, homogeneity and static properties, effective space dimensions, quark confinement...) can also be relevant at these energies. In particular, UHECR data would in principle allow to set bounds on Lorentz symmetry violation (LSV) in patterns incorporating a privileged local reference frame (the vacuum rest frame, VRF). But the precise analysis is far from trivial, and other effects can also be present. The effective parameters can be related to Planck-scale physics, or even to physics beyond Planck scale, as well as to the dynamics and effective symmetries of LSV for nucleons, quarks, leptons and the photon. LSV can also be at the origin of GZK-like effects. In the presence of a VRF, and contrary to a grand unification view, LSV and other violations of standard principles can modify the internal structure of particles at very high energy and conventional symmetries may cease to be valid at energies close to the Planck scale. We present an updated discussion of these topics, including experimental prospects, new potentialities for high-energy cosmic ray phenomenology and the possible link with unconventional pre-Big Bang scenarios, superbradyon (superluminal preon) patterns... The subject of a possible superluminal propagation of neutrinos at accelerator energies is also dealt with. (Contribution to the International Conference on New Frontiers in Physics, ICFP 2012, Kolymbari, Crete, June 10-16 2012)

Geometrical Dark Energy and Lorentz Symmetry Violation in Brane-worlds

Geometrical Dark Energy and Lorentz Symmetry Violation in Brane-worlds

Ultra-high energy physics and standard basic principles

It has not yet been elucidated whether the observed flux suppression for ultra- high energy cosmic rays (UHECR) at energies above � 4x1 0 19 eV is a signature of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or a consequence of other phenomena. In both cases, violations of the standard fundamental principles of Physics can be present and play a significant role. They can in particular modify cosmic-ray interactions, prop- agation or acceleration at very high energy. Thus, in a long-term program, UHECR data can hopefully be used to test relativity, quantum mechanics, energy and momentum con- servation, properties... as well as the elementariness of standard particles. Data on cosmic rays at energies � 10 20 eV may also be sensitive to new physics generated well beyond Planck scale. A typical example is provided by the search for possible sig- natures of a Lorentz symmetry violation (LSV) associated to a privileged local reference frame (the vacuum rest frame, VRF). If a VRF exists, the internal structure of standard particles at ultra-high energy can undergo substantial modifications. Similarly, the con- ventional particle symmetries may cease to be valid at such energies instead of heading to a grand unification and the structure of may no longer be governed by standard quantum field theory. Then, the question whether the notion of Planck scale still makes sense clearly becomes relevant and the very grounds of Cosmology can undergo essential modifications. UHECR studies naturally interact with the interpretation of WMAP and Planck observations. Recent Planck data analyses tend to confirm the possible existence of a privileged space direction. If the observed phenomenon turns out to be a signature of the spinorial space-time (SST) we suggested in 1996-97, then conventional Particle Physics may correspond to the local properties of standard matter at low enough energy and large enough distances. This would clearly strengthen the cosmological relevance of UHECR phenomenology and weaken the status of the Planck scale hypothesis. Another crucial observation is that, already before incorporating standard matter and relativity, the SST geometry naturally yields a Ht = 1 law where t is the age of the Universe and H the ratio between relative speeds and distances at cosmic scale. As standard cosmology is not required to get such a fundamental result, the need for a conventional Planck scale is far from obvious and the study of UHECR can potentially yield evidence for an alter- native approach including new physics and new ultimate constituents of matter. UHECR may in particular allow to explore the possible indications of the existence of a transition scale at very high energy where the standard laws would start becoming less and less dominant and new physics would replace the conventional fundamental principles. We discuss prospects of searches for potential signatures of such a phenomenon.

Spontaneous Broken Local Conformal Symmetry and Dark Energy Candidate

The local conformal symmetry is spontaneously broken down to the Local Lorentz invariance symmetry through the approach of nonlinear realization. The resulting effective Lagrangian, in the unitary gauge, describes a cosmological vector field non-minimally coupling to the gravitational field. As a result of the Higgs mechanism, the vector field absorbs the dilaton and becomes massive, but with an independent energy scale. The Proca type vector field can be modelled as dark energy candidate. The possibility that it further triggers Lorentz symmetry violation is also pointed out.

Rashba coupling induced by Lorentz symmetry breaking effects

The arising of a Rashba‐like coupling, a Zeeman‐like term and a Darwin‐like term induced by Lorentz symmetry breaking effects in the non‐relativistic quantum dynamics of a spin‐1/2 neutral particle interacting with external fields is studied. Moreover, the influence of a Rashba‐like coupling induced by a Lorentz symmetry violation background on the Tan–Inkson potential [W.‐C. Tan and J. C. Inkson, Semicond. Sci. Technol.11, 1635 (1996)] is discussed.

Anandan quantum phase and quantum holonomies induced by the effects of the Lorentz symmetry violation background in the CPT-even gauge sector of the Standard Model Extension

We study the rise of geometric quantum phases corresponding to the analogues of the Anandan quantum phase (J. Anandan, Phys. Lett. A 138, 347 (1989)) based on possible scenarios of the Lorentz symmetry violation background in the CPT-even gauge sector of the Standard Model Extension. We also show that we can obtain quantum holonomies associated with the analogues of the Anandan quantum phase, and discuss a possible analogy with the holonomic quantum computation (P. Zanardi, M. Rasetti, Phys. Lett. A 264, 94 (1999)).

Limits on violations of Lorentz symmetry from Gravity Probe B

Generic violations of Lorentz symmetry can be described by an effective field theory framework that contains both general relativity and the standard model of particle physics called the Standard-Model Extension (SME). We obtain new constraints on the gravitational sector of the SME using recently published final results from Gravity Probe B. These include for the first time an upper limit at the 10^(-3) level on the time-time component of the new tensor field responsible for inducing local Lorentz violation in the theory, and an independent limit at the 10^(-7) level on a combination of components of this tensor field.

The photino sector and a confining potential in a supersymmetric Lorentz-symmetry-violating model

We study the spectrum of the minimal supersymmetric extension of the Carroll-Field-Jackiw model for Electrodynamics with a topological Chern-Simons-like Lorentz-symmetry violating term. We identify a number of independent background fermion condensates, work out the gaugino dispersion relation and propose a photonic effective action to consider aspects of confinement induced by the SUSY background fermion condensates, which also appear to signal Lorentz-symmetry violation in the photino sector of the action. Our calculations of the static potential are carried out within the framework of the gauge-invariant but path-dependent variables formalism which are alternative to the Wilson loop approach. Our results show that the interaction energy contains a linear term leading to the confinement of static probe charges.

Fermion effective dispersion relation forz=2Lifshitz QED

We study consequences of Lorentz symmetry violation in a $z=2$ Lifshitz extension of QED in $3+1$ dimensions, and we discuss nontrivial effects of quantization. Because of the specific power of space momentum in propagators of the model, dimensional regularization leads to an unusual interpretation of loop integrals, which are finite even when the space dimension goes to the integer 3. We check the consistency of the approach by calculating the (vanishing) corrections to the photon mass and the IR-divergence-free corrections to the dispersion relation for massless fermions.

Quantum holonomies based on the Lorentz-violating tensor background

We study geometric quantum phases corresponding to analogues of the Anandan quantum phase (Anandan 1989 Phys. Lett. A 138 347) based on a possible scenario of the Lorentz-symmetry violation background in a tensor background. We also show that quantum holonomies associated with the analogue of the Anandan quantum phase can be determined, and discuss a way of performing one-qubit quantum gates by analogy with the holonomic quantum computation (Zanardi and Rasetti 1999 Phys. Lett. A 264 94).