Two-dimensional magnetoexcitons in the presence of spin-orbit coupling

We study theoretically the effect of spin-orbit coupling on quantum well excitons in a strong magnetic field. We show that, in the presence of an in-plane field component, the excitonic absorption spectrum develops a double-peak structure due to hybridization of bright and dark magnetoexcitons. If the Rashba and Dresselhaus spin-orbit constants are comparable, the magnitude of splitting can be tuned in a wide interval by varying the azimuthal angle of the in-plane field. We also show that the interplay between spin-orbit and Coulomb interactions leads to an anisotropy of exciton energy dispersion in the momentum plane. The results suggest a way for direct optical measurements of spin-orbit parameters.Comment: 9 pages, 6 figure

Effects of Turbulent Mixing on the Critical Behavior

Effects of strongly anisotropic turbulent mixing on the critical behavior are studied by means of the renormalization group. Two models are considered: the equilibrium model A, which describes purely relaxational dynamics of a nonconserved scalar order parameter, and the Gribov model, which describes the nonequilibrium phase transition between the absorbing and fluctuating states in a reaction-diffusion system. The velocity is modelled by the d-dimensional generalization of the random shear flow introduced by Avellaneda and Majda within the context of passive scalar advection. Existence of new nonequilibrium types of critical regimes (universality classes) is established.Comment: Talk given in the International Bogolyubov Conference "Problems of Theoretical and Mathematical Physics" (Moscow-Dubna, 21-27 August 2009

Non-Linear Algebra and Bogolubov's Recursion

Numerous examples are given of application of Bogolubov's forest formula to iterative solutions of various non-linear equations: one and the same formula describes everything, from ordinary quadratic equation to renormalization in quantum field theory.Comment: LaTex, 21 page

Sequential superradiant scattering from atomic Bose-Einstein condensates

We theoretically discuss several aspects of sequential superradiant scattering from atomic Bose-Einstein condensates. Our treatment is based on the semiclassical description of the process in terms of the Maxwell-Schroedinger equations for the coupled matter-wave and optical fields. First, we investigate sequential scattering in the weak-pulse regime and work out the essential mechanisms responsible for bringing about the characteristic fan-shaped side-mode distribution patterns. Second, we discuss the transition between the Kapitza-Dirac and Bragg regimes of sequential scattering in the strong-pulse regime. Finally, we consider the situation where superradiance is initiated by coherently populating an atomic side mode through Bragg diffraction, as in studies of matter-wave amplification, and describe the effect on the sequential scattering process.Comment: 9 pages, 4 figures. Submitted to Proceedings of LPHYS'06 worksho

The Minimum Stellar Mass in Early Galaxies

The conditions for the fragmentation of the baryonic component during merging of dark matter halos in the early Universe are studied. We assume that the baryonic component undergoes a shock compression. The characteristic masses of protostellar molecular clouds and the minimum masses of protostars formed in these clouds decrease with increasing halo mass. This may indicate that the initial stellar mass function in more massive galaxies was shifted towards lower masses during the initial stages of their formation. This would result in an increase of the number of stars per unit halo mass, i.e., the efficiency of star formation.Comment: 18 pages, 7 figure

Observational Manifestations of the First Protogalaxies in the 21 cm Line

The absorption properties of the first low-mass protogalaxies (mini-halos) forming at high redshifts in the 21-cm line of atomic hydrogen are considered. The absorption properties of these protogalaxies are shown to depend strongly on both their mass and evolutionary status. The optical depths in the line reach $\sim$0.1-0.2 for small impact parameters of the line of sight. When a protogalaxy being compressed, the influence of gas accretion can be seen manifested in a non-monotonic frequency dependence of the optical depth. The absorption characteristics in the 21-cm line are determined by the thermal and dynamical evolution of the gas in protogalaxies. Since the theoretical line width in the observer's reference frame is 1-6 kHz and the expected separation between lines 8.4 kHz, the lines from low mass protogalaxies can be resolved using ongoing and future low frequency interferometers.Comment: 12 pages, 5 figure

Study of the ρ\rho, ω\omega, ϕ→ηγ→7γ\phi\to\eta\gamma\to 7\gamma Decays with an SND Detector on a VEPP-2M Collider

The $e^+e^-\to\eta\gamma\to 7\gamma$ process was studied in the energy range $2E=600\div 1060$ MeV with an SND detector on a VEPP-2M $e^+e^-$ collider. The decay branching ratios $B(\phi\to\eta\gamma)=(1.343\pm 0.012\pm 0.055)\cdot 10^{-2}$, $B(\omega\to\eta\gamma)=(4.60\pm 0.72\pm 0.19)\cdot 10^{-4}$, and $B(\rho\to\eta\gamma)=(2.69\pm 0.32\pm 0.16)\cdot 10^{-4}$ were measured.Comment: 5 pages, 4 figure

Magnetic Resonance of the Intrinsic Defects of the Spin-Peierls Magnet CuGeO3

ESR of the pure monocrystals of CuGeO3 is studied in the frequency range 9-75 GHz and in the temperature interval 1.2-25 K. The splitting of the ESR line into several spectral components is observed below 5 K, in the temperature range where the magnetic susceptibility is suppressed by the spin-Peierls dimerization. The analysis of the magnetic resonance signals allows one to separate the signals of the S=1/2- and S=1 defects of the spin-Peierls phase. The value of g-factor of these signals is close to that of the Cu-ion. The additional line of the magnetic resonance is characterized by an anomalous value of the g-factor and by the threshold-like increase of the microwave susceptibility when the microwave power is increasing. The ESR signals are supposingly attributed to two types of the planar magnetic defects, arising at the boundaries of the domains of the spin-Peierls state with the different values of the phase of the dimerization.Comment: LATEX-text, 12 PS-figures, typos corrected, LATEX-style change

Finite temperature nonlocal effective action for quantum fields in curved space

Massless and massive scalar fields and massless spinor fields are considered at arbitrary temperatures in four dimensional ultrastatic curved spacetime. Scalar models under consideration can be either conformal or nonconformal and include selfinteraction. The one-loop nonlocal effective action at finite temperature and free energy for these quantum fields are found up to the second order in background field strengths using the covariant perturbation theory. The resulting expressions are free of infrared divergences. Spectral representations for nonlocal terms of high temperature expansions are obtained.Comment: 32 pages, LaTe

Modeling of the Magnetic Susceptibilities of the Ambient- and High-Pressure Phases of (VO)_{2}P_{2}O_{7}

The magnetic susceptibilities chi versus temperature T of powders and single crystals of the ambient-pressure (AP) and high-pressure (HP) phases of (VO)_{2}P_{2}O_{7} are analyzed using an accurate theoretical prediction of chi(T, J1, J2) for the spin-1/2 antiferromagnetic alternating-exchange (J1, J2) Heisenberg chain. The results are consistent with recent models with two distinct types of alternating-exchange chains in the AP phase and a single type in the HP phase. The spin gap for each type of chain is derived from the respective set of two fitted alternating exchange constants and the one-magnon dispersion relation for each of the two types of chains in the AP phase is predicted. The influences of interchain coupling on the derived intrachain exchange constants, spin gaps, and dispersion relations are estimated using a mean-field approximation for the interchain coupling. The accuracies of the spin gaps obtained using fits to the low-T chi(T) data by theoretical low-T approximations are determined. The results of these studies are compared with previously reported estimates of the exchange couplings and spin gaps in the AP and HP phases and with the magnon dispersion relations in the AP phase measured previously using inelastic neutron scattering.Comment: 25 two-column REVTeX pages, 16 embedded figures, 6 tables. Figures 9 and 10 and Sec. IIIC revised due to errors in Eq. (1) of Ref. 24 which gives the theoretical one-magnon dispersion relation for coupled alternating-exchange chains. Minor revisions also made in other section