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.     

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.     

Opening the axion window

In this paper I consider models where the strong CP problem is solved by means of a Peccei-Quinn symmetry carried by exotic colored fermions. An example is Kim's recently proposed composite invisible axion model. Axions from such models don't couple to electrons, and have model dependent photon couplings which may differ from the standard coupling by a factor of 10^?2 ? 10⁺¹. As a result, laboratory detection of relic axions may be very difficult, and astrophysical bounds on the axion mass are weakened. Pulsar observations place no strong bound on such an axion unless the core is known not to be superfluid. Normal fusion stars allow an axion mass as large as $\text{m}{}_{\mathrm{<mtext>a</mtext>}}\text{? 20}\text{eV}$ for certain models.     

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.     

Detecting solar axions using Earth's magnetic field

We show that solar axion conversion to photons in the Earth's magnetosphere can produce an x-ray flux, with average energy omega approximately 4 keV, which is measurable on the dark side of the Earth. The smallness of the Earth's magnetic field is compensated by a large magnetized volume. For axion masses m(a) less, similar10(-4) eV, a low-Earth-orbit x-ray detector with an effective area of 10(4) cm(2), pointed at the solar core, can probe the photon-axion coupling down to 10(-11) GeV-1, in 1 yr. Thus, the sensitivity of this new approach will be an order of magnitude beyond current laboratory limits.     

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.     

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.     

Two-vertex loop diagrams in the two-dimensional subspace induced by a superstrong magnetic field: polarization operator and photon and axion decay to neutrinos

The absence of divergences and singularities in effectively two-dimensional field theory induced by a superstrong magnetic field is demonstrated for the example where loop diagrams involving two vector and two pseudovector vertices are calculated. The form of effective low-energy Lagrangians for (γνν) and (aνν) interactions in a superstrong magnetic field is presented. The role of photon and axion decays to neutrinos in the early universe is discussed.     

Influence of strongly magnetized plasma on photon splitting

The photon splitting γ → γγ in a strongly magnetized medium of arbitrary temperature and chemical potential is considered. In comparison with the case of a pure magnetic field, a new photon splitting channel is shown to be possible below the electron-positron pair production threshold. The partial splitting amplitudes and probabilities are calculated by taking into account the photon dispersion in a strong magnetic field and a charge-symmetric plasma. An enhancement of the photon splitting probability compared to the case of a magnetic field without plasma has been found to be possible under certain conditions.     

Large non-gaussianity in axion inflation

The inflationary paradigm has enjoyed phenomenological success; however, a compelling particle physics realization is still lacking. Axions are among the best-motivated inflaton candidates, since the flatness of their potential is naturally protected by a shift symmetry. We reconsider the cosmological perturbations in axion inflation, consistently accounting for the coupling to gauge fields cΦFF, which is generically present in these models. This coupling leads to production of gauge quanta, which provide a new source of inflaton fluctuations, δΦ. For c≥10(2)M(p)(-1), these dominate over the vacuum fluctuations, and non-Gaussianity exceeds the current observational bound. This regime is typical for concrete realizations that admit a UV completion; hence, large non-Gaussianity is easily obtained in minimal and natural realizations of inflation.     

Electromagnetic catalysis of the radiative decay of the axion

The radiative decay of the axion a → γγ is investigated in an external electromagnetic field in DFSZ model in which axion couples to both quarks and leptons at tree level. The decay probability is strongly catalyzed by the external field, namely, the field removes the main suppression caused by the smallness of the axion mass.     

Axions and “light shining through a wall”: A detailed theoretical analysis

We give a detailed study of axion-photon and photon-axion conversion amplitudes, which enter the analysis of “light shining through a wall” experiments. Several different calculational methods are employed and compared, and in all cases we retain a nonzero axion mass. To leading order, we find that when the photon frequency ω is very close to the axion mass m, there is a threshold cusp which significantly enhances the photon to axion conversion amplitude, by a factor relative to the corresponding axion to photon conversion process. When m=0, the enhancement factor reduces to unity and the results of previous calculations are recovered. Our calculations include an exact wave matching analysis, which shows how unitarity is maintained near threshold at ω=m, and a discussion of the case when the magnetic field extends into the “wall” region.     

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.     

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.     

Magnetic properties of a two-dimensional spatially ordered array of nickel nanowires

The structural and magnetic characteristics of two-dimensional spatially ordered arrays of magnetic nickel nanowires embedded in the anodized alumina template have been investigated. It has been shown using small-angle polarized-neutron diffraction that, there exists the samples under investigation, in a highly ordered hexagonal structure of pores and magnetic nanowires separated by a characteristic distance d = 106 ± 2 nm. An analysis has been made of different contributions to neutron scattering, such as the nonmagnetic (nuclear) contribution, the magnetic contribution dependent on the magnetic field, and the interference contribution indicating a correlation between the magnetic and nuclear structures. The performed analysis of the results obtained has demonstrated that, when the magnetic field is applied perpendicular to the longitudinal axis of the nanowire in a completely magnetized sample, there arise demagnetizing fields around each nanowire that form a regular hexagonal lattice.     

Pseudoscalar particle-photon interaction induced by an external magnetic field in an electron-positron plasma

The effective interaction of a pseudoscalar particle with a photon in a magnetized electron-positron plasma is investigated. The plasma and field contributions to the effective coupling between the pseudoscalar particle and the photon are calculated. The effective coupling is shown to be independent of the parameters of the medium and the particle 4-momentum in certain limiting cases.     

Strange Quark Matter and Strangelets in a Strong Magnetic Field

We study the stability properties of magnetized strange quark matter and strangelets under a strong magnetic field in the MIT bag model. The free energy per baryon of strange quark matter feels a great influence from the magnetic field. At the field strength about 10¹⁷G, the magnetized strange quark matter becomes more stable. Considering the finite size effect, the magnetic influence on strangelets becomes complicated. For a given magnetic field, there exists a critical baryon number, below which the magnetized strangelets have lower energy than the non-magnetized strangelets. For the field strength of 5× 10¹⁷G, the critical baryon number is A_c ～ 100. Generally, the critical baryon number increases with the decreasing external magnetic field. When the field strength is smaller than 10¹⁷G, the critical baryon number goes up to A_c～ 10⁵. The stable radius, electric charge, and quark flavor fractions of magnetized strangelets are shown.     

电磁场中光子-轴子的转化微分截面

运用费曼微扰方法分别计算了在磁偶极场、电偶极场和均匀静电场及静磁场中光子转化成轴子的非极化微分截面.在电偶极场中,沿光子传播方向及其反方向上的非极化微分截面为零;而在磁偶极场中,在上述方向上通常则具有非零的微分截面,但当光子传播方向平行于磁场偶极距矢量时,该微分截面为零.在均匀的静磁场和均匀静电场中,只有在光子传播方向及其反方向上具有非零的微分截面,但后者小于前者.在轴子质量趋于零的极限条件下,上述过程和光子转化为引力子的过程表现出某些非常类似的性质. 关键词： 轴子 光子 微分截面     

The magnetic fields and rotation generators of free space electromagnetism

The relation is developed between rotation generators of the Lorentz group and the magnetic fields of free-space electromagnetism. Using these classical relations, it is shown that in the quantum field theory there exists a longitudinal photomagneton, a quantized magnetic flux density operator which is directly proportional to the photon spin angular momentum. Commutation relations are given in the quantum field between the longitudinal photomagneton and the usual transverse magnetic components of quantized electromagnetism. The longitudinal component is phase free, but the transverse components are phase dependent. All three components can magnetize material in general, but only the transverse components contribute to Planck's law. The photon therefore has three, not two, relativistically invariant degrees of polarization, an axial, longitudinal, polarization, and the usual right and left circular transverse polarizations. Since the longitudinal polarization is axial, it is a phase- free magnetic field.