The topological susceptibility in `full' (UK)QCD

We report first calculations of the topological susceptibility measured using the field theoretic method on SU(3) gauge configurations produced by the UKQCD collaboration with two flavours of dynamical, improved, Wilson fermions. Using three ensembles with matched lattice spacing but differing sea quark mass we find that hybrid Monte Carlo simulation appears to explore the topological sectors efficiently, and a topological susceptibility consistent with increasing linearly with the quark mass.Comment: LaTeX. 4 PostScript figures. Contribution to LATTICE99(topology

Topology in CP(N-1) models: a critical comparison of different cooling techniques

Various cooling methods, including a recently introduced one which smoothes out only quantum fluctuations larger than a given threshold, are applied to the study of topology in 2d CP(N-1) models. A critical comparison of their properties is performed.Comment: Poster at LATTICE99(Topology and confinement), 3 pages, 5 eps figures, uses espcrc2.st

3-D lattice simulation of the electroweak phase transition at small Higgs mass

We study the electroweak phase transition by lattice simulations of an effective 3-dimensional theory, for a Higgs mass of about $35 GeV$. In the broken symmetry phase our results on masses and the Higgs condensate are consistent with 2-loop perturbative results. However, we find a non-perturbative lowering of the transition temperature, similar to the one previously found at $m_H = 80 GeV$. For the symmetric phase, bound state masses and the static force are determined and compared with results for pure $SU(2)$ theory.Comment: 11 pages, uuencoded ps-file, 5 postscript figures include

Scalar-isoscalar states in the large-Nc Regge approach

Scalar-isoscalar states (0++) are investigated within the large-Nc Regge approach. We elaborate on the consequences of including the lightest f0(600) scalar-isoscalar state into such an analysis, where the position of f0(600) fits very well into the pattern of the radial Regge trajectory. Furthermore, we point out that the pion and nucleon spin-0 gravitational form factors, recently measured on the lattice, provide valuable information on the low-mass spectrum of the scalar-isoscalar states on the basis of the scalar-meson dominance in the spin-0 channel. Through the fits to these data we find m_sigma= 450-600 MeV. We compare the predictions of various fits and methods. An analysis of the QCD condensates in the two-point correlators provides further constraints on the parameters of the scalar-isoscalar sector. We find that a simple two-state model suggests a meson nature of f0(600), and a glueball nature of f0(980), which naturally explains the ratios of various coupling constants. Finally, we note that the fine-tuned condition of the vanishing dimension-2 condensate in the Regge approach with infinitely many scalar-isoscalar states yields a reasonable value for the mass of the lighest glueball state.Comment: 18 pages, 13 figures. Typos corrected. Remarks and references adde

The Spatial String Tension in High Temperature Lattice Gauge Theories

We develop some techniques which allow an analytic evaluation of space-like observables in high temperature lattice gauge theories. We show that such variables are described extremely well by dimensional reduction. In particular, by using results obtained in the context of ``Induced QCD'', we evaluate the contributions to space-like observables coming from the Higgs sector of the dimensionally reduced action, we find that they are of higher order in the coupling constant compared to those coming from the space-like action and hence neglegible near the continuum limit. In the case of SU(2) gauge theory our results agree with those obtained through Montecarlo simulations both in (2+1) and (3+1) dimensions and they also indicate a possible way of removing the gap between the two values of $g^2(T)$ recently appeared in the literature.Comment: 17 pages, (Latex), DFTT 8/9

Improving the topological charge density operator on the lattice

We analyze the properties of a class of improved lattice topological charge density operators, constructed by a smearing-like procedure. By optimizing the choice of the parameters introduced in their definition, we find operators having (i) a much better statistical behavior as estimators of the topological charge density on the lattice, i.e. much less noisy; (ii) a multiplicative renormalization much closer to one; (iii) a large suppression of the perturbative tail in the corresponding lattice topological susceptibility.Comment: 4 pages, to be published in the Proceedings of Lattice 95, uuencoded postscript fil