Equivalence principle and electromagnetic field: no birefringence,no dilaton,and no axion

The coupling of the electromagnetic field to gravity is discussed. In the premetric axiomatic approach based on the experimentally well established conservation laws of electric charge and magnetic flux, the Maxwell equations are the same irrespective of the presence or absence of gravity. In this sense, one can say that the charge “substratum” and the flux “substratum” are not influenced by the gravitational field directly. However, the interrelation between these fundamental substrata, formalized as the spacetime relation H = H(F) between the 2-forms of the electromagnetic excitation H and the electromagnetic field strength F, is affected by gravity. Thus the validity of the equivalence principle for electromagnetism depends on the form of the spacetime relation. We discuss the nonlocal and local linear constitutive relations and demonstrate that the spacetime metric can be accompanied also by skewon, dilaton, and axion fields. All these premetric companions of the metric may eventually lead to a violation of the equivalence principle.     

The natural line-breadth in stochastic electrodynamics

The fact that the formalism of stochastic electrodynamics includes the reaction force, makes the calculation of the natural line-breadth straightforward. The evaluation of the relativistic correction to energy levels is greatly simplified in stochastic electrodynamics and brings out the concept of the propagation of the Coulomb field with the velocity of electromagnetic waves.     

Shock wave polarizations and optical metrics in the Born and the Born–Infeld electrodynamics

We analyze the behavior of shock waves in nonlinear theories of electrodynamics. For this, by use of generalized Hadamard step functions of increasing order, the electromagnetic potential is developed in a series expansion near the shock wave front. This brings about a corresponding expansion of the respective electromagnetic field equations which allows for deriving relations that determine the jump coefficients in the expansion series of the potential. We compute the components of a suitable gauge-normalized version of the jump coefficients given for a prescribed tetrad compatible with the shock front foliation. The solution of the first-order jump relations shows that, in contrast to linear Maxwell’s electrodynamics, in general the propagation of shock waves in nonlinear theories is governed by optical metrics and polarization conditions describing the propagation of two differently polarized waves (leading to a possible appearance of birefringence). In detail, shock waves are analyzed in the Born and Born–Infeld theories verifying that the Born–Infeld model exhibits no birefringence and the Born model does. The obtained results are compared to those ones found in literature. New results for the polarization of the two different waves are derived for Born-type electrodynamics.     

Photonic crystal fibers with material anisotropy

In this paper we are modeling the interplay of material and form birefringence in photonic crystal fibers. We introduce an efficient numerical method for the calculation of the modal structure. Our approach relies solving the fully vectorial wave equation for the transverse magnetic field and the respective propagation constants using a plane wave expansion. The method accounts for a simple form of material anisotropy. Our analysis is relevant to certain application areas, and in particular to fiber sensing, where material birefringence arises for instance due to transversally applied mechanical stress. We analyze the influence of material birefringence on the modal birefringence and the state of polarization of the fundamental mode.     

Instability in magnetic materials with a dynamical axion field

It has been pointed out that axion electrodynamics exhibits instability in the presence of a background electric field. We show that the instability leads to a complete screening of an applied electric field above a certain critical value and the excess energy is converted into a magnetic field. We clarify the physical origin of the screening effect and discuss its possible experimental realization in magnetic materials where magnetic fluctuations play the role of the dynamical axion field.     

Electromagnetic wave scattering by an external field

The quantum electrodynamics of bilocal fields is used to calculate the triangular Feynman diagrams describing the elastic scattering of a classical electromagnetic wave by an external Coulomb field. The total contribution of the diagrams is nonzero because of the violation of both the Furry theorem (CP or T symmetries) and the Ward identities. The cross section for this scattering process is found for low and high energies. A comparison with Compton scattering and Euler—Heisenberg scattering is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 38–47, August 1995.     

Reconciliation of the forward scattering and wave theories of electric-field-gradient-induced birefringence

We consider propagation of a linearly polarized, harmonic, plane electromagnetic wave incident on a dilute gas subject to a non-uniform electrostatic field. We work to electric quadrupole–magnetic dipole order. In general, the wave is distorted to include a perpendicular component induced by the electrostatic field gradient, and the resultant is not a plane wave. Although the induced component is small, its contribution to the polarization-dependent refractive index of the gas in Buckingham's quadrupole experiment is significant. We show that distortion of the incident wave accounts exactly for the present discrepancy between wave theory and forward scattering theory of electric-field-gradient-induced birefringence in a gas: both theories yield the result obtained originally by Buckingham and Longuet-Higgins.     

P, T violating magneto-electro-optics

We study linear and bilinear magneto-electro-optical effects due to the propagation of light in centro-symmetric media in the presence of P, T violating interactions and external transverse and longitudinal electric and/or magnetic fields. We show that new magneto-electric optical effects appear. In particular, we show the existence of a Jones birefringence proportional to the square of the transverse field amplitude. All these effects are an unambiguous signature of the P, T violation, and a search for such new phenomena could also provide novel limits on electric dipole moment (EDM) of matter.     

A Process Algebra Approach to Quantum Electrodynamics

The process algebra program is directed towards developing a realist model of quantum mechanics free of paradoxes, divergences and conceptual confusions. From this perspective, fundamental phenomena are viewed as emerging from primitive informational elements generated by processes. The process algebra has been shown to successfully reproduce scalar non-relativistic quantum mechanics (NRQM) without the usual paradoxes and dualities. NRQM appears as an effective theory which emerges under specific asymptotic limits. Space-time, scalar particle wave functions and the Born rule are all emergent in this framework. In this paper, the process algebra model is reviewed, extended to the relativistic setting, and then applied to the problem of electrodynamics. A semiclassical version is presented in which a Minkowski-like space-time emerges as well as a vector potential that is discrete and photon-like at small scales and near-continuous and wave-like at large scales. QED is viewed as an effective theory at small scales while Maxwell theory becomes an effective theory at large scales. The process algebra version of quantum electrodynamics is intuitive and realist, free from divergences and eliminates the distinction between particle, field and wave. Computations are carried out using the configuration space process covering map, although the connection to second quantization has not been fully explored.     

Electric field effect on refraction of light in a layer of chiral liquid crystal with large pitch

The effect of an alternating electric field on the trajectory of an extraordinary light wave in a layer of a chiral liquid crystal with a 180° turn of the director is studied. In this structure, in the absence of the field and at a large angle of incidence of the light wave on the liquid crystal layer, the light undergoes refraction inside the layer. It is shown that the deformation of the director that arises under the action of the electric field changes the character of refraction of the extraordinary wave and the layer begins to transmit the light. The threshold voltage of this effect is determined. The dynamics of the effect is studied. At large voltages, in addition to the extraordinary wave, an ordinary light wave is observed in the light passed through the cell. The ordinary wave intensity is modulated by the initial frequency of the control signal, whereas the extraordinary wave intensity is modulated by the double initial frequency.     

Kerr effect caused by an electric current in a weakly ionized gas

The anisotropy of the velocity distribution caused by an electric current in a fluid leads to a molecular alignment via the non-spherical interaction. This alignment implies a birefringence proportional to the square of the applied electric field just as the ordinary Kerr effect. The kinetic theory of this phenomenon is presented for a lorentzian mixture, viz. a gas of few light charged linear molecules and of many heavy optically isotropic particles. The current-induced contribution to the Kerr effect turns out to be much larger than the contribution which stems from the usually considered orienting influence of the electric field on anisotropic molecules.     

Formal Similarity Between Mathematical Structures of Electrodynamics and Quantum Mechanics

Electromagnetic phenomena can be described by Maxwell equations written for the vectors of electric and magnetic field. Equivalently, electrodynamics can be reformulated in terms of an electromagnetic vector potential. We demonstrate that the Schrödinger equation admits an analogous treatment. We present a Lagrangian theory of a real scalar field φ whose equation of motion turns out to be equivalent to the Schrödinger equation with time independent potential. After introduction the field into the formalism, its mathematical structure becomes analogous to those of electrodynamics. The field φ is in the same relation to the real and imaginary part of a wave function as the vector potential is in respect to electric and magnetic fields. Preservation of quantum-mechanics probability is just an energy conservation law of the field φ.     

Doubled conformal compactification

We use Weyl transformations between the Minkowski spacetime and dS/AdS spacetime to show that one cannot well define the electrodynamics globally on the ordinary conformal compactification of the Minkowski spacetime (or dS/AdS spacetime), where the electromagnetic field has a sign factor (and thus is discountinuous) at the light cone. This problem is intuitively and clearly shown by the Penrose diagrams, from which one may find the remedy without too much difficulty. We use the Minkowski and dS spacetimes together to cover the compactified space, which in fact leads to the doubled conformal compactification. On this doubled conformal compactification, we obtain the globally well-defined electrodynamics.     

Axion self-energy in a magnetic field

The axion self-energy in an external magnetic field is investigated. It is shown that, in addition to the standard contribution due to axion interaction with virtual fermions, there exists the contribution induced by photon exchange. For the two contributions, expressions that take exactly into account an external field are obtained, and the limit of an ultrastrong magnetic field is explored for them. The question of whether two-dimensional QED, which effectively arises in the limit of a strong magnetic field, is applicable to calculating the virtual-fermion-induced contribution to the axion self-energy is analyzed.     

Propagation of an arbitrary incident light in a uniaxially planar slab

Similarly to the Jones calculus, a propagation formulation of an arbitrary incident light in a uniaxially planar slab with any orientation of the optic axis is derived, where both the multi-reflections and multi-refractions and the phase difference between the ordinary and extraordinary waves arising at the interface are considered. Unlike the case of propagation in the stratified isotropic media, the elements of the reflection and transmission matrices not only include the reflection and transmission coefficients, but also comprise phase differences caused by the mutual couples between ordinary (O) and extraordinary (E) waves. At this point, the propagation of an arbitrary light in a stratified uniaxially anisotropic media may be viewed as the multi-reflections and multi-refractions of a compound wave composed of one O wave and one E wave.     

Localized axion photon states in a strong magnetic field

We consider the axion field and electromagnetic waves with rapid time dependence, coupled to a strong time independent, asymptotically approaching a constant at infinity “mean” magnetic field, which takes into account the back reaction from the axion field and electromagnetic waves with rapid time dependence in a time averaged way. The direction of the self consistent mean field is orthogonal to the common direction of propagation of the axion and electromagnetic waves with rapid time dependence and parallel to the polarization of these electromagnetic waves. Then, there is an effective U(1) symmetry mixing axions and photons. Using the natural complex variables that this U(1) symmetry suggests we find localized planar soliton solutions. These solutions appear to be stable since they produce a different magnetic flux than the state with only a constant magnetic field, which we take as our “ground state”. The solitons also have non-trivial U(1) charge defined before, different from the uncharged vacuum. These solitons represent a new, non-gravitational mechanism, of trapping light. They could also affect the vacuum structure in models of the QCD vacuum that incorporate a magnetic condensate, introducing may be gluon axion solitons.     

Nonlinear electrodynamics and anisotropic space-time

The metrical properties of four-space in the presence of a nonlinear electromagnetic field in vacuum are investigated. It is shown that the metric induced by the nonlinear electromagnetic field has a complicated nature and corresponds to an anisotropic space-time, i.e., to a four-space in which birefringence is observed. A special case of such a space is ordinary Riemann-Euclid space. As an example, the influence on the metric of the radiative corrections that follow from quantum electrodynamics is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 52–55, April, 1980.     

Vacuum Polarization in Self-Field Quantum Electrodynamics

We have evaluated analytically the vacuum polarization in a Coulomb field using the relativistic Dirac-Coulomb wave functions by a new method. The result is made finite by an appropriate choice of contour integrations and gives the standard result in the lowest order of iteration. We used the formalism of self-field quantum electrodynamics in the evaluation of the vacuum polarization which needs neither field quantization nor renormalization. There are no infrared or ultraviolet divergences.     

Entanglement of light-shift compensated atomic spin waves with telecom light

Entanglement of a 795 nm light polarization qubit and an atomic Rb spin-wave qubit for a storage time of 0.1 s is observed by measuring the violation of Bell's inequality (S=2.65±0.12). Long qubit storage times are achieved by pinning the spin wave in a 1064 nm wavelength optical lattice, with a magic-valued magnetic field superposed to eliminate lattice-induced dephasing. Four-wave mixing in a cold Rb gas is employed to perform light qubit conversion between near infrared (795 nm) and telecom (1367 nm) wavelengths, and after propagation in a telecom fiber, to invert the conversion process. Observed Bell inequality violation (S=2.66±0.09), at 10 ms storage, confirms preservation of memory-light entanglement through the two stages of light qubit frequency conversion.