Spin-order-induced multiferroicity in LiCuFe2(VO4)3 and disorder effects in NaCuFe2(VO4)3

Mixed spin chain compounds, ACuFe2(VO4)3 (A= Li,Na), reach magnetically ordered state at TN ~ 11 K (Li) or ~ 9 K (Na) and experience further transformation of magnetic order at T* ~ 7 K (Li) or ~ 5 K (Na), evidenced in magnetic susceptibility chi and specific heat Cp measurements. While no anomaly has been detected in dielectric property of NaCuFe2(VO4)3, the step-like feature precedes a sharp peak in permittivity epsilon at TN in LiCuFe2(VO4)3. These data suggest the spin-order-induced ferroelectricity in Li compound and no such thing in Na compound. On the contrary, the Moessbauer spectroscopy study suggests similarly wide distribution of hyperfine field in between T* and TN for both the compounds. The first principles calculations also provide similar values for magnetic exchange interaction parameters in both compounds. These observations lead us to conclude on the crucial role of alkali metals mobility within the channels of the crystal structure needed to be considered in explaining the improper multiferroicity in one compound and its absence in other.Comment: 9 pages, 5 figure

A nonlinear approach to NN interactions using self-interacting meson fields

Motivated by the success of models based on chiral symmetry in NN interactions we investigate self-interacting scalar, pseudoscalar and vector meson fields and their impact for NN forces. We parametrize the corresponding nonlinear field equations and get analytic wavelike solutions. A probability amplitude for the propagation of particle states is calculated and applied in the framework of a boson-exchange NN potential. Using a proper normalization of the meson fields makes all self-scattering amplitudes finite. The same normalization is able to substitute for the phenomenological form factors used in conventional boson exchange potentials and thus yields an phenomenological understanding of this part of the NN interaction. We find an empirical scaling law which relates the meson self-interaction couplings to the pion mass and self-interaction coupling constant. Our model yields np phase shifts comparable to the Bonn B potential results and deuteron properties, in excellent agreement with experimental data.Comment: Reviewed version, 25 pages REVTeX, more info at http://i04ktha.desy.d

Why pair production cures covariance in the light-front?

We show that the light-front vaccum is not trivial, and the Fock space for positive energy quanta solutions is not complete. As an example of this non triviality we have calculated the electromagnetic current for scalar bosons in the background field method were the covariance is restored through considering the complete Fock space of solutions. We also show thus that the method of "dislocating the integration pole" is nothing more than a particular case of this, so that such an "ad hoc" prescription can be dispensed altogether if we deal with the whole Fock space. In this work we construct the electromagnetic current operator for a system composed of two free bosons. The technique employed to deduce these operators is through the definition of global propagators in the light front when a background electromagnetic field acts on one of the particles.Comment: 11 pages, 2 figure

КОЛЛИНЕАРНОЕ АКУСТООПТИЧЕСКОЕ ВЗАИМОДЕЙСТВИЕ БЕССЕЛЕВЫХ СВЕТОВЫХ ПУЧКОВ В ДВУОСНЫХ КРИСТАЛЛАХ

The collinear acousto-optic transformation of Bessel light beams into two ring beams of internal conical refraction has been considered. Using the Fourier transformation method, the expressions for power flows of ring diffracted beams of internal conical refraction are found in closed form. For a potassium biftalate crystal, the dependence of the diffraction efficiency on the ultrasound intensity and interaction durability is calculated. Based on this interaction, the creation of collinear convertible AO filters with a narrow width of a transmission band of about 0.1 is proposed. Рассмотрено коллинеарное акустооптическое преобразование бесселевых световых пучков в два кольцевых пучка внутренней конической рефракции. С использованием метода преобразования Фурье найдены выражения для потоков мощности дифрагированных кольцевых пучков внутренней конической рефракции в замкнутой форме. Для кристалла бифталата калия произведен расчет зависимости эффективности дифракции от интенсивности ультразвука и длины взаимодействия. На основе данного взаимодействия предложено создание коллинеарных перестраиваемых АО фильтров с узкой шириной полосы пропускания, достигающей 0,1 Å.

ПРЕОБРАЗОВАНИЕ ДВУМЕРНЫХ КВАЗИБЕЗДИФРАКЦИОННЫХ СВЕТОВЫХ ПУЧКОВ ПРИ АКУСТООПТИЧЕСКОМ ВЗАИМОДЕЙСТВИИ В ОДНООСНЫХ КРИСТАЛЛАХ

Participants of shape transformation of two-dimensional nearly absent-diffracted (cosine-supergaussian) light beams under Braggs diffraction by ultrasonic waves in iniaxial gyrotropic crystals are investigated. It is shown that at diffraction of such light beams travelling in the vicinity of the crystal optical axis on a slow shear ultrasonic wave under the conditions of a strong acoustooptical interaction, light beams experience a significant deformation of the intensity distribution in the beam cross section. At large widths of a supergaussian component of an incident beam, the shape of a diffracted beam remains underchanged. It is stated that the diffraction efficiency weakly depends on the width of the supergaussian component of the cosine-supergaussian beam.Исследованы особенности преобразований формы двумерных квазибездифракционных (косинус-супергауссовых) световых пучков при брэгговской дифракции на ультразвуковых волнах в одноосных гиротропных кристаллах. Показано, что при дифракции таких световых пучков, распространяющихся вблизи оптической оси кристалла на медленной сдвиговой УЗ-волне в условиях сильного акустооптического взаимодействия, дифрагированные световые пучки испытывают существенную деформацию распределения интенсивности в поперечном сечении пучка. При больших ширинах супергауссовой составляющей падающего пучка форма дифрагированного пучка остается неизменной. Установлено, что эффективность дифракции слабо зависит от ширины супергауссовой составляющей косинус-супергауссового пучка

Excitonic Strings in one dimensional organic compounds

Important questions concern the existence of excitonic strings in organic compounds and their signatures in the photophysics of these systems. A model in terms of Hard Core Bosons is proposed to study this problem in one dimension. Mainly the cases with two and three particles are studied for finite and infinite lattices, where analytical results are accessible. It is shown that if bi-excitonic states exist, three-excitonic and even, n-excitonic strings, at least in a certain range of parameters, will exist. Moreover, the behaviour of the transitions from one exciton to the biexciton is fully clarified. The results are in agreement with exact finite cluster diagonalizations of several model Hamiltonians.Comment: 36 pages, 4 eps figs. to appear in Phys. Rev.

Consistent description of NN and pi-N interactions using the solitary boson exchange potential

A unified description of NN and pi-N elastic scattering is presented in the framework of the one solitary boson exchange potential (OSBEP). This model already successfully applied to analyze NN scattering is now extended to describe pi-N scattering while also improving its accuracy in the NN domain. We demonstrate the importance of regularization of pi-N scattering amplitudes involving Delta isobars and derivative meson-nucleon couplings, as this model always yields finite amplitudes without recourse to phenomenological form factors. We find an empirical scaling relation of the meson self interaction coupling constants consistent with that previously found in the study of NN scattering. Finally, we demonstrate that the OSBEP model does not contradict the soft-pion theorems of pi-N scattering.Comment: 29 pages RevTeX, submitted to Phys. Rev. C, further information at http://i04ktha.desy.d

Interference effects in the decay \phi\to \pi^{0}\pi^{0}\gamma and the coupling constant g_{\phi\sigma\gamma}

We study the radiative decay $\phi\to\pi^{0}\pi^{0}\gamma$ within the framework of a phenomenological approach in which the contributions of $\sigma$-meson, $\rho$-meson and $f_0$-meson are considered. We analyze the interference effects between different contributions and utilizing the experimental branching ratio for this decay we estimate the coupling constant $g_{\phi\sigma\gamma}$.Comment: 12 Pages in REVTEX, 5 Figures, to be published in Phys.Rev.

Measurement of associated charm production induced by 400 GeV/c protons

An important input for the interpretation of the measurements of the SHiP ex- periment is a good knowledge of the differential charm production cross section, including cascade production. This is a proposal to measure the associated charm production cross section, employing the SPS 400 GeV/c proton beam and a replica of the first two interaction lengths of the SHiP target. The detection of the produc- tion and decay of charmed hadron in the target will be performed through nuclear emulsion films, employed in an Emulsion Cloud Chamber target structure. In order to measure charge and momentum of decay daughters, we intend to build a mag- netic spectrometer using silicon pixel, scintillating fibre and drift tube detectors. A muon tagger will be built using RPCs. An optimization run is scheduled in 2018, while the full measurement will be performed after the second LHC Long Shutdown