We study various properties of bosons in two dimensions interacting only via onsite hardcore repulsion. In particular, we use the lattice spin-wave approximation to calculate the ground state energy, the density, the condensate density and the superfluid density in terms of the chemical potential. We also calculate the excitation spectrum, ω(k). In addition, we performed high precision numerical simulations using the stochastic series expansion algorithm. We find that the spin-wave results describe extremely well the numerical results over the whole density range 0 ≤ ρ ≤ 1. We also compare the lattice spin-wave results with continuum results obtained by summing the ladder diagrams at low density. We find that for ρ ≤ 0.1 there is good agreement, and that the difference between the two methods vanishes as ρ 2 for ρ → 0. This offers the possibility of obtaining precise continuum results by taking the continuum limit of the spin-wave results for all densities. Finaly, we studied numerically the finite temperature phase transition for the entire density range and compared with low density predictions.

Brief Reports are short papers which report on completed research which, while meeting the usual Physical Review standards of scientific quality, does not warrant a regular article (A. ddenda to papers previously published in the Physical Review by the same authors are included in Brief Reports )A. Brief Report may be no longer than 3g printed pages and must be accompanied by an abstract. The same publication schedule as for regular articles is followed, and page proofs are sent to authors We study some statistical properties of a turbulent state described by a generalized Ginzburg-Landau equation and characterized by topological defects.

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Using two methods, via fluctuations and correlations, an analytical formula is derived for the factorial multiplicity moments in a QCD jet at the Double Leading Logarithm accuracy. The resulting self-similar dependence on the solid-angle cell size is characteristic of an intermittency behaviour in angular variables. The intermittency indices depend on the diffusion angle through the running of α s . Physical features of jet fluctuations such as collimation at large angles and saturation at small angles are well described in the perturbative framework. A parameter-free prediction of angular intermittency is proposed for Z 0 decays into hadrons, assuming hadron-parton duality.