XMM-Newton Observations of Evolution of Cluster X-Ray Scaling Relations at z=0.4-0.7

We present a spatially-resolved analysis of the temperature and gas density profiles of galaxy clusters at z=0.4-0.7 observed with XMM-Newton. These data are used to derive the total cluster mass within the radius r_500 without assuming isothermality, and also to measure the average temperature and total X-ray luminosity excluding the cooling cores. We derive the high-redshift M-T and L-T relations and compare them with the local measurements. The high-redshift L-T relation has low scatter and evolves as L ~ (1+z)^{1.8\pm0.3} for a fixed T, in good agreement with several previous Chandra and XMM-Newton studies (Vikhlinin et al., Lumb et al., Maughan et al.). The observed evolution of the M-T relation follows M_500 = A T^{3/2} E(z)^{-alpha}, where we measure alpha=0.88\pm0.23. This is in good agreement with predictions of the self-similar theory, alpha=1.Comment: ApJ in press, updated to match the accepted versio

Single hole dynamics in dimerized spin liquids

The dynamics of a single hole in quantum antiferromagnets is influenced by magnetic fluctuations. In the present work we consider two situations. The first one corresponds to a single hole in the two leg t-J spin ladder. In this case the wave function renormalization is relatively small and the quasiparticle residue of the S=1/2 state remains close to unity. However at large t/J there are higher spin (S=3/2,5/2,..) bound states of the hole with the magnetic excitations, and therefore there is a crossover from quasiparticles with S=1/2 to quasiparticles with higher spin. The second situation corresponds to a single hole in two coupled antiferromagnetic planes very close to the point of antiferromagnetic instability. In this case the hole wave function renormalization is very strong and the quasiparticle residue vanishes at the point of instability.Comment: 12 pages, 3 figure

A library of routines for incoherent scatter radar data processing

The structure of the developed dynamic link library of routines for incoherent scatter radar data processing and incoherently scattered signals simulation and the examples of its application are described.У статті описано структуру розробленої динамічної бібліотеки процедур для обробки даних радара некогерентного розсіяння та імітації некогерентно розсіяних сигналів, а також приведено приклади її використання

Spin polaron in the J1-J2 Heisenberg model

We have studied the validity of the spin polaron picture in the frustrated J1-J2 Heisenberg model. For this purpose, we have computed the hole spectral functions for the Neel, collinear, and disordered phases of this model, by means of the self-consistent Born approximation and Lanczos exact diagonalization on finite-size clusters. We have found that the spin polaron quasiparticle excitation is always well defined for the magnetically ordered Neel and collinear phases, even in the vicinity of the magnetic quantum critical points, where the local magnetization vanishes. As a general feature, the effect of frustration is to increase the amplitude of the multimagnon states that build up the spin polaron wave function, leading to the reduction of the quasiparticle coherence. Based on Lanczos results, we discuss the validity of the spin polaron picture in the disordered phase.Comment: 9 pages, 12 figure

Bound states of magnons in the S=1/2 quantum spin ladder

We study the excitation spectrum of the two-leg antiferromagnetic S=1/2 Heisenberg ladder. Our approach is based on the description of the excitations as triplets above a strong-coupling singlet ground state. The quasiparticle spectrum is calculated by treating the excitations as a dilute Bose gas with infinite on-site repulsion. We find singlet (S=0) and triplet (S=1) two-particle bound states of the elementary triplets. We argue that bound states generally exist in any dimerized quantum spin model.Comment: 4 REVTeX pages, 4 Postscript figure

New quantum phase transitions in the two-dimensional J1-J2 model

We analyze the phase diagram of the frustrated Heisenberg antiferromagnet, the J1-J2 model, in two dimensions. Two quantum phase transitions in the model are already known: the second order transition from the Neel state to the spin liquid state at (J_2/J_1)_{c2}=0.38, and the first order transition from the spin liquid state to the collinear state at (J_2/J_1)_{c4}=0.60. We have found evidence for two new second order phase transitions: the transition from the spin columnar dimerized state to the state with plaquette type modulation at (J_2/J_1)_{c3}=0.50(2), and the transition from the simple Neel state to the Neel state with spin columnar dimerization at (J_2/J_1)_{c1}=0.34(4). We also present an independent calculation of (J_2/J_1)_{c2}=0.38 using a new approach.Comment: 3 pages, 5 figures; added referenc