Microscopic description of relaxation of impurity magnetic atoms in spiral magnetics

Kinetics of the impurity magnetic atoms in spiral magnetic is researched. The spectrum of the excitations of the impurity spin is obtained in approximation of weakly coupling. The equation for impurity density matrix up to second order of the perturbation theory is obtained. For impurity spin s=1/2 the kinetic coefficients in terms of correlation functions are found

Modulation instability in two component Bose-Einstein condensate with relative component motion

The development of modulation instability in a spatially homogeneous two-component Bose-Einstein condensate (BEC), in which the interacting components move through each other at a relative speed, is investigated. It is shown that nonlinear dynamics, leading to modulation instability, is determined by both the values of the constant interaction and the relative velocity between the components. The maximum oscillation increment is found and the limits of the existence of modulation instability in the space of wave numbers are determined.Досліджується розвиток модуляційної нестійкості в просторово-однорідному двокомпонентному бозеейнштейнівському конденсаті (БЕК), в якому взаємодіючі компоненти рухаються один відносно одного зі швидкістю VR. Показано, що нелінійна динаміка, яка веде до модуляційної нестійкості, визначається як величинами постійних взаємодій, так і відносною швидкістю між компонентами. Знайдено максимальний інкремент коливань і визначено межі існування модуляційної нестійкості в просторі хвильових чисел.Исследуется развитие модуляционной неустойчивости в пространственно-однородном двухкомпонентном бозе-эйнштейновском конденсате (БЭК), в котором взаимодействующие компоненты движутся друг относительно друга со скоростью VR. Показано, что нелинейная динамика, приводящая к модуляционной неустойчивости, определяется как величинами постоянных взаимодействия, так и относительной скоростью между компонентами. Найден максимальный инкремент колебаний и определены границы существования модуляционной неустойчивости в пространстве волновых чисел

Nonlocal effect influence on the vortex filament structure in Bose-gas

Using the Gross-Pitaevskii equation (GPE), which accounts for a weak non-locality effects, we study the structure of the vortex filaments in a Bose-gas. We show that the sign of the additional terms in the generalized GPE depends on the form of the interaction potential and can be positive or negative. The generalized GPE for a single vortex is solved numerically. It is demonstrated that the non-locality can cause either an increase or a decrease of the vortex core radius.С помощью уравнения Гросса-Питаевского (ГП), учитывающего эффект слабой нелокальности, исследована структура вихревой нити в бозе-газе. Показано, что знак постоянной перед дополнительным слагаемым в обобщенном уравнении ГП зависит от вида потенциала взаимодействия и может быть как положительным, так и отрицательным. Обобщенное уравнение ГП для одиночного вихря решено численно. Показано, что учет эффекта нелокальности может приводить как к увеличению, так и к уменьшению радиуса сердцевины вихря.За допомогою рівняння Гросса-Питаєвського (ГП), яке враховує ефект малої нелокальності, досліджена структура вихру у надплинному бозе-конденсаті. Показано, що знак сталої перед додатковим доданком в узагальненому рівнянні ГП залежить від потенціалу взаємодії і може бути як додатнім, так і від'ємним. Узагальнене рівняння ГП для одинарного вихру розв'язано чисельно. Показано, що врахування ефекту нелокальності може привести як до збільшення, так і до зменшення радіусу серцевини вихру

On equilibrium states of superfluid with d-wave pairing

The equilibrium states of quantum fluid with d-pairing classification is carried out on the basis of the quasiaverages concept. It is shown, that the set of such an equilibrium states can be classified in the terms of the orbital momentum quantum number, relevant to the projection of the orbital momentum of the superconducting electron pair on an anisotropy direction. The explicit expression of three admissible unbroken symmetry generators and relevant order parameter equilibrium values are found

Volume element structure and roton-maxon-phonon excitations in superfluid helium beyond the Gross-Pitaevskii approximation

We propose a theory which deals with the structure and interactions of volume elements in liquid helium II. The approach consists of two nested models linked via parametric space. The short-wavelength part describes the interior structure of the fluid element using a non-perturbative approach based on the logarithmic wave equation; it suggests the Gaussian-like behaviour of the element's interior density and interparticle interaction potential. The long-wavelength part is the quantum many-body theory of such elements which deals with their dynamics and interactions. Our approach leads to a unified description of the phonon, maxon and roton excitations, and has noteworthy agreement with experiment: with one essential parameter to fit we reproduce at high accuracy not only the roton minimum but also the neighboring local maximum as well as the sound velocity and structure factor.Comment: 9 pages, 6 figure

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results