Coherent backscattering in nematic liquid crystals in an external magnetic field

We consider multiple light scattering in a nematic liquid crystal. Using the Monte Carlo method, we calculate for the first time the effect of a magnetic field on the shape of the peak of coherent backscattering taking into account the long-range action of fluctuations of the orientational order and anisotropy of the scattering length. For a small number of initial and final scattering events, we take into account the ordinary mode of light, which is weakly scattered in a nematic liquid crystal (NLC), whereas a strongly scattered extraordinary mode is taken into account for all scattering events. For simplicity, we use a single-constant approximation of the NLC elastic moduli. We show that the angular shape of the peak of coherent backscattering remains nearly unchanged, whereas the magnetic field and the scattering phase function vary by several orders of magnitude.     

Coherent backscattering of nonmonochromatic light by an ensemble of cold atoms

The coherent backscattering of light by an ensemble of cold atoms in a magneto-optical trap is studied theoretically. The effect of the width and shape of the incident light spectrum on the enhancement factor and total intensity of the backscattered light is analyzed. The calculations are performed for ⁸⁵Rb atoms with allowance for the entire hyperfine and Zeeman structure of the ground and excited states of the atoms, spatial inhomogeneity of the atomic cloud, and motion of the atoms.     

Coherent radiation under conditions of the propagation of heavy charged particles through the dielectric in an external electric field

The process of electromagnetic radiation arising during the propagation of heavy charged particles through a dielectric layer situated in an external electric field is investigated. This radiation is due to the degradation of polarization medium induced by the field. The local maximum within the centimeter frequency range of the energy spectrum is analyzed under varying external parameters of the model. Conditions that might allow for the intensity of the radiation to be comparable to the transition radiation are found.     

Neutrino transitions in an external field

In the article the transitionv _e f v is considered in a field of plane-wave type, induced by the effective values of the anomalous magnetic and electric dipole moments of massive neutrinos. The possible contribution of the given mechanism to the background of quantum mechanical oscillatory phenomena is discussed.Moscow State Correspondence Pedagogical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 31–35, January, 1993.     

Magnetic fluids in an external field

Within mean field approximation we investigate the phase diagrams of magnetic fluids in presence of a magnetic field. In a finite field the magnetic phase transition is absent, but instead a line of first order liquid-liquid transitions ending in a critical point occurs for a magnetic interaction, which is sufficiently strong. Varying the magnetic field these critical points extend from the tricritical point at H=0 to a critical endpoint. For a fluid with Ising spins we calculate the critical lines and several tricritical exponents analytically. For Heisenberg fluids we obtain the phase diagrams from a numerical solution of the mean field equations of state. Received 20 March 1998     

Renormalization of QED in an external field

The Schwinger equations of QED are rewritten in three different ways as integral equations involving functional derivatives, which are called weak field, strong field, and SCF quantum electrodynamics. The perturbative solutions of these equations are given in terms of appropriate Feynman diagrams. The Green function that is used as an electron propagator in each case is discussed in detail. The general renormalization rules for each of the three equations are provided both in a non perturbative way (Dyson relations) and for Feynman diagrams.     

Coherent population trapping in an ensemble of three-level atoms in the presence of cooperative relaxation

We derive equations that describe the dynamics of three-level atoms with a cascade system of levels interacting with two resonant coherent fields in conditions where cooperative relaxation dominates over incoherent spontaneous emission. We calculate the temporal dynamics of the values of the atomic populations. The possibility of coherent population trapping in the presence of the cooperative decay is established. Finally, we calculate the averaged population of the intermediate level as a function of detuning for different values of the coupling constant. Zh. éksp. Teor. Fiz. 112, 869–876 (September 1997)     

Two-dimensional antiferromagnet in an external staggered field

We calculate the temperature-dependent energy gap in the magnetic excitations spectrum of the two-dimensional antiferromagnet in the presence of a staggered magnetic field, using the nonlinear sigma model.     

Green's functions in an external electromagnetic field

The possibility is discussed of using eigenfunctions to find different propagators in quantum electrodynamics (QED) with an external electromagnetic field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 59–64, May, 1989.The authors are grateful to B. L. Voronov and I. V. Tyutin for useful discussion of the questions examined here.     

Dirac oscillator in an external magnetic field

We show that (2+1)-dimensional Dirac oscillators in an external magnetic field is mapped onto the same with reduced angular frequency in absence of magnetic field. This can be used to study the atomic transitions in a radiation field. Relativistic Landau levels are constructed explicitly. Several interesting features of this system are discussed.     

Surface states in an external electric field

In an electric field typical for field ion microscopy, true surface states can exist. Their shift towards higher energies can be quite significant, and moreover, additional surface levels at still higher energies can appear.     

Coherent modes in an ensemble of quantum dots generated by dynamic dipole–dipole interactions

The generation and stabilization of coherent modes induced by electric dipole–dipole interactions in a quantum dot ensemble are verified, by means of a standard interaction Hamiltonian scheme, and also by way of a full quantum mechanical path integral on the coherent state basis.     

Symmetry of a molecule in an external field

It is stated that, although an external field distorts a rigid molecule, it does not destroy internal geometric symmetry of its dynamics, which is specified by a point group. As a consequence, degeneracies of stationary states connected with this group are preserved. This statement makes it possible to describe the spectrum of a molecule in an external field based only on symmetry principles, which is exemplified by the linear Zeeman effect.     

Neutrino decay of an axion in an external electromagnetic field

Switching on an external electromagnetic field opens a neutrino decay channel of a hypothetical pseudoscalar particle, an axion, which plays an important role in modern field theory. We obtain exact expressions in the one-loop approximation for the probability of the decay into a massless neutrino in a crossed fieldF and study the asymptotic behavior by the nature of the parameter . Moscow State Industrial University, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 2, pp. 8–12, February, 1999.     

Green's function of an electron in an external electromagnetic field

New field-theoretical representations are obtained for Green's function of an electron in an external electromagnetic field, making it possible to simplify its calculation substantially.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 33–37, February, 1982.     

Heterolayer screening of an external ion field

The theory of screening by heterolayer carriers, in their ground sub-band, is used to investigate the conditions in which the classical image charge applies to the polarization by an external ion field. An estimate of the field penetrating to the far side of the heterolayer is obtained.     

Interaction with an external field in quantum electrodynamics

Russian Physics Journal -     

XY spin fluid in an external magnetic field

A method of integral equations is developed to study anisotropic fluids with planar spins in an external field. As a result, the calculations for these systems appear to be no more difficult than those for ordinary homogeneous liquids. The approach proposed is applied to the ferromagnetic XY spin fluid in a magnetic field using a soft mean spherical closure and the Born-Green-Yvon equation. This provides an accurate reproduction of the complicated phase diagram behavior obtained by cumbersome Gibbs ensemble simulation and multiple histogram reweighting techniques.