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.     

Photon and axion splitting in an inhomogeneous magnetic field

The axion–photon system in an external magnetic field, when the direction of propagation of axions and photons is orthogonal to the direction of the external magnetic field, displays a continuous axion–photon duality symmetry in the limit the axion mass is neglected. The conservation law that follow in this effective (2+1)$(2+1)$-dimensional theory from this symmetry is obtained. The magnetic field interaction is seen to be equivalent to first order to the interaction of a complex charged field with an external electric potential, where this fictitious “electric potential” is proportional to the external magnetic field. This allows one to solve for the scattering amplitudes using already known scalar QED results. From the scalar QED analog the axion and the photon are symmetric and antisymmetric combinations of particle and antiparticle. If one considers therefore scattering experiments in which the two spatial dimensions of the effective theory are involved nontrivially, one observes that both particle and antiparticle components of photons and axions are preferentially scattered in different directions, thus producing the splitting or decomposition of the photon and axion into their particle and antiparticle components in an inhomogeneous magnetic field. This observable in principle effect is of first order in the axion–photon coupling, unlike the “light shining through a wall phenomena”, which is second order.     

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.     

The search for axions

The axion is a light pseudoscalar particle predicted to exist as a consequence of the Peccei–Quinn solution to the strong-CP problem. Its abundant production in the early Universe along with its stability and insignificant interaction cross-section make it a prime dark matter candidate. This report summarises the search for dark matter axions using resonant microwave cavities as well as searches for axions produced in the Sun and in the laboratory. All of these current experiments focus on the axion–photon interaction, as coherent axion–photon mixing in strong magnetic fields of large spatial extent can make up for the extraordinary weakness of the the coupling of axions to photons.     

Propagation of electromagnetic waves in a waveguide with a modulated anisotropic insert

The propagation of transverse electric (TE) and transverse magnetic (TM) waves in a waveguide of arbitrary cross section with an anisotropic periodically space-and time-modulated insert is considered. Under the assumption that the modulation indices are small, analytical expressions for the TE and TM fields in the domain of weak interaction between the signal wave and modulating wave are derived. The frequency near which strong interaction between these waves occurs is found, and specific features of the fields in this domain are revealed.     

Interaction of counterpropagating electromagnetic waves in an absorbing plate inside a waveguide

The interaction of two counterpropagating coherent transverse electric and transverse magnetic electromagnetic waves in an absorbing plate that is placed in a waveguide with an arbitrary transverse cross section is analyzed. It is assumed that the waves with different initial phases are incident on the plate boundaries from two sides. An analytical expression for the interference transmission coefficient with respect to power is derived. Several physical features of the tunneling interference in the plate are revealed. It is demonstrated that a scenario in which an electromagnetic energy flux exists on the left-hand side of the plate and vanishes on the right-hand side or vice versa is possible at certain relations of the initial phases and amplitudes of the counterpropagating waves.     

Nichtlineare Wechselwirkung elektromagnetischer Wellen im Plasma mit konstantem Magnetfeld

The nonlinear interaction of waves in anisotropic plasmas is considered. Solving the hydrodynamics equations with a n-th order perturbation procedure, an equation for the nonlinear electric field is derived. The n-th order current produced by interaction of waves with lower order is represented by means of a nonlinear tensor of conductivity, which is calculated for n = 2. It is shown, that a miced plasma wave with combination frequencies is excited as the result of interaction of two transverse (ordinary) waves propagating perpendicular to the magnetic field.     

Pseudo-scalar photon mixing in a magnetized medium

Axions are pseudo-scalar particles, those which arise because of breaking of Peccei Queen (PQ) symmetry. Axions have a tree level coupling to two photons. As a consequence there exists a tree level coupling of axion to photon in a magnetic field. However, in an external magnetic field, there exists a new loop induced, axion photon vertex that gives rise to axion photon coupling. The strength of the tree level axion photon coupling in magnetic field is known to be model dependent. However, in a magnetic field, the new loop induced coupling has some interesting features. This note discusses the new axion photon vertex in a magnetized medium and the corrections arising from there. The magnitude of the correction to axion photon coupling, because of magnetized vacuum and matter, is estimated in this note. While making this estimate we note that the form of the axion photon vertex is related to the axial polarization tensor. This vertex is shown to satisfy the Ward identity. The coupling is shown to have a momentum dependent piece in it. Astrophysical importance of this extra modification is also pointed out.     

Large Dynamical Axion Field in Topological Antiferromagnetic Insulator Mn_2Bi_2Te_5

The dynamical axion field is a new state of quantum matter where the magnetoelectric response couples strongly to its low-energy magnetic fluctuations.It is fundamentally different from an axion insulator with a static quantized magnetoelectric response.The dynamical axion field exhibits many exotic phenomena such as axionic polariton and axion instability.However,these effects have not been experimentally confirmed due to the lack of proper topological magnetic materials.Combining analytic models and first-principles calculations,here we predict a series of van der Waals layered Mn_2Bi_2Te_5-related topological antiferromagnetic materials that could host the long-sought dynamical axion field with a topological origin.We also show that a large dynamical axion field can be achieved in antiferromagnetic insulating states close to the topological phase transition.We further propose the optical and transport experiments to detect such a dynamical axion field.Our results could directly aid and facilitate the search for topological-origin large dynamical axion field in realistic materials.     

Gradient models of the axion–photon coupling

We establish an extended version of the Einstein–Maxwell-axion model by introducing into the Lagrangian cross-terms, which contain the gradient four-vector of the pseudoscalar (axion) field in convolution with the Maxwell tensor. The gradient model of the axion–photon coupling is applied to cosmology: we analyze the Bianchi-I type Universe with an initial magnetic field, electric field induced by the axion–photon interaction, cosmological constant and dark matter, which is described in terms of the pseudoscalar (axion) field. Analytical, qualitative and numerical results are presented in detail for two distinguished epochs: first, for the early Universe with magnetic field domination; second, for the stage of late-time accelerated expansion.     

Polarization-Independent Directional Beaming of Light by a Subwavelength Metal Slit

We present the directional beaming effect of light at the terahertz frequency by using a subwavelength slit in the metal film. The metal is dressed with anisotropic dielectric so that both the transverse electric （TE） and transverse magnetic （TM） polarized waves can be well guided on the metal surface and reach the phase matching. By using a periodical array of dielectric ridges and grooves around the slit, the guided waves can be scattered out of the slit and interfere with the transmitted light directly through the slit. The results performed by finite-difference at time-domain computations indicate that the directional beaming of light can be obtained simultaneously for both the TE and TM polarized waves after optimizing the geometric parameters. The structure may find great applications in polarization-independent optical devices such as couplers, connectors, beam collimator, and etc.     

The peculiarities of coupled electromagnetic and magnetoelastic waves in antiferromagnets

A spectrum of coupled electromagnetic, spin and elastic waves in a two-sublattice antiferromagnet with weak ferromagnetism is theoretically investigated. The influence of the g-factor anisotropy and the transverse and longitudinal relaxation in magnetic subsystem on the spectrum of coupled waves is considered. The most changes of dispersion laws occurred in long-wavelength approximation and near the spin reorientation point, then the vectors of ferromagnetism and antiferromagnetism reoriented onto another crystallographic axis. It is shown that the magnetoelastic, the Dzyaloshinsky and the dipole interactions, the anisotropy of g-factor, the external magnetic field and the longitudinal susceptibility determine the activation of quasiferromagnetic waves. The dispersion laws of quasielectromagnetic and quasielastic waves can change from linear dependence to square. At large damping in magnetic subsystem, one from these modes can become the pure relaxation one.     

Polarization properties of surface plasmon polaritons at the boundary of topological insulators with the axion effect

Properties of surface plasmon polariton waves are theoretically studied in structures containing topological insulators with the axion effect. The effect of axion properties on dispersion, localization, and polarization of plasmon polaritons is analyzed. A possibility of determining the axion effect from the variation in the plasmon-polariton polarization is shown, and conditions for enhancement of polarization effects are revealed in waveguide structures of the dielectric?metal?dielectric type.     

Second-order bragg interaction in double grating couplers: TM mode

An analytical treatment of the second-order Bragg interaction is presented for the transverse magnetic mode of a dielectric film waveguide having gratings on both the film-cover and the film-substrate interfaces. Four canonical equations that describe the interactions of two guided waves propagating in the opposite directions in the film and the normally incident and radiated free waves in the cover and the substrate are deduced.     

随机磁场对静电波驱动的速度扩散的影响

随机磁场改变了波与粒子之间的耦合关系。因而使波驱动的速度扩散受到影响。其结果是:波电场的横向分量可以对纵向速度扩散有贡献;∈<<1情形,扩散系数的共振峰被展宽;∈>>1情形,扩散系数的振荡效应被削弱。当随机磁场的关联时间与波的特征时间之间相对大小不同时,随机磁场产生影响的具体机制不完全相同,所造成的后果也有差别。对于接近于在垂直方向传播的波,随机磁场对速度扩散的影响一般是重要的。     

Waveguide interaction of light with spin waves in a ferromagnetic film

We discuss the results of a theoretical analysis of the waveguide interaction of light and spin waves. Both linear and quadratic magnetooptical effects are taken into account. The features of the interaction are considered for the three principal types of spin waves: waves in a normally magnetized ferromagnetic film, and longitudinal and transverse waves in a tangentially magnetized film. Isotropic and anisotropic diffraction processes are considered. Numerical estimates of the intensity and frequency properties of the diffraction scattering are given for a number of situations of practical interest. The effect of a strong constant magnetic field on the interaction of light and spin waves is considered.Translated from Izvestiya Vyssnikh Uchebnykh Zavednii, Fizika, No. 4, pp. 5–31, April, 1989.     

Production of axions by cosmic magnetic helicity

We investigate the effects of an external magnetic helicity production on the evolution of the cosmic axion field. It is shown that a helicity larger than (few x 10(-15) G)2 Mpc, if produced at temperatures above a few GeV, is in contradiction with the existence of the axion, since it would produce too much of an axion relic abundance.     

Magnetic-field influence on radiative axion decay into photons of the same polarization

The decays of a pseudoscalar particle, the axion, into two photons of the same polarization are studied in the model involving direct axion-electron coupling. These processes, which are forbidden in a vacuum because of a pseudoscalar nature of the axion, become possible in a magnetic field. It is shown that the kinematics of ultrarelativistic-axion decay substantially depends on photon polarizations. The probability of radiative axion decay in the limit of a strong magnetic field substantially exceeds the corresponding probability in a vacuum.     

Axion emission from a magnetized neutron gas

By using the polarization density matrix for a neutron in a magnetic field, the axion luminosity of magnetic neutron stars that is associated with the flip of the anomalous magnetic moment of degenerate nonrelativistic neutrons is calculated. It is shown that, at values of the magnetic-field induction in the region B ≳ 10¹⁸ G, this mechanism of axion emission is dominant in “young” neutron stars of temperature about a few tens of MeV units. At B ∼ 10¹⁷ G, it is one of the basic mechanisms. The Fermi energy of a degenerate neutron gas in a magnetic field is found, and it is shown that there is no such mechanism of axion emission in the degenerate case.     

Acoustic self-induced transparency for transverse waves in a system with resonant and quasi-resonant transitions

A theoretical analysis of acoustic self-induced transparency is presented for transverse elastic waves propagating perpendicular to an applied magnetic field through a crystal with spin-3/2 paramagnetic impurities. The interaction between an acoustic pulse and magnetic field is described by Maxwell-Bloch-type equations for a system with transitions inhomogeneously broadened because of a quadrupole Stark shift. If the pulse carrier frequency is resonant with one transition and quasi-resonant with another transition, then the evolution of a one-dimensional pulse is described by an integrable Konno-Kameyama-Sanuki (KKS) equation. The underlying physics of its soliton solution and the corresponding behavior of the medium are analyzed. Self-focusing and self-trapping conditions are found for a pulse of finite transverse size. In the latter regime, the pulse stretches along the propagation direction, transforming into a “hollow bullet,” while its transverse size remains constant.