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

Instantons and Monopoles in the Maximally Abelian Gauge

We study the Abelian projection of SU(2) instantons in the Maximally Abelian gauge. We find that in this gauge an isolated instanton produces a closed monopole loop within its core and the size of this loop increases with the core size. We show that this result is robust against the introduction of small quantum fluctuations. We investigate the effects of neighbouring (anti)instantons upon each other and show how overlapping (anti)instantons can generate larger monopole loops. We find, however, that in fields that are typical of the fully quantised vacuum only some of the large monopole loops that are important for confinement have a topological origin. We comment on what this may imply for the role of instantons in confinement and chiral symmetry breaking.Comment: 14 pages LaTeX plus 5 PostScript figures. Uses epsf.sty. Self-unpacking, uuencoded tar-compressed fil

Z2 monopoles in D=2+1 SU(2) lattice gauge theory

We calculate the Euclidean action of a pair of Z2 monopoles (instantons), as a function of their spatial separation, in D=2+1 SU(2) lattice gauge theory. We do so both above and below the deconfining transition at T=Tc. At high T, and at large separation, we find that the monopole `interaction' grows linearly with distance: the flux between the monopoles forms a flux tube (exactly like a finite portion of a Z2 domain wall) so that the monopoles are linearly confined. At short distances the interaction is well described by a Coulomb interaction with, at most, a very small screening mass, possibly equal to the Debye electric screening mass. At low T the interaction can be described by a simple screened Coulomb (i.e. Yukawa) interaction with a screening mass that can be interpreted as the mass of a `constituent gluon'. None of this is unexpected, but it helps to resolve some apparent controversies in the recent literature.Comment: 14 pages, 2 figure

Vortices and confinement in hot and cold D=2+1 gauge theories

We calculate the variation with temperature of the vortex free energy in D=2+1 SU(2) lattice gauge theories. We do so both above and below the deconfining transition at T=Tc. We find that this quantity is zero at all T for large enough volumes. For T<Tc this observation is consistent with the fact that the phase is linearly confining; while for T>Tc it is consistent with the conventional expectation of `spatial' linear confinement. In small spatial volumes this quantity is shown to be non-zero. The way it decreases to zero with increasing volume is shown to be controlled by the (spatial) string tension and it has the functional form one would expect if the vortices being studied were responsible for the confinement at low T, and for the `spatial' confinement at large T. We also discuss in detail some of the direct numerical evidence for a non-zero spatial string tension at high T, and we show that the observed linearity of the (spatial) potential extends over distances that are large compared to typical high-T length scales.Comment: 27 pages, 6 figure

Gauge Theory in d=2+1 at High Temperature: Z_N interface

We calculate on the lattice the interface tension in the SU(2) pure gauge theory in d=2+1 at high temperature. The result is compared to the perturbative prediction. The agreement confirms applicability of the perturbation theory in this case.Comment: Lattice'94 contribution, 3pp, uuencoded compressed postscrip

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

The topological susceptibility and f_pi from lattice QCD

We study the topological susceptibility, chi, in QCD with two quark flavours using lattice field configurations that have been produced with an O(a) improved quark action. We find clear evidence for the expected suppression at small quark mass, and examine the variation of chi with this mass. The resulting estimate of the pion decay constant, f_pi = 105 +/- 6 ^{+18}_{-10} MeV, is consistent with the experimental value of ~93 MeV. We compare chi to the large-N_c prediction and find consistency over a large range of quark masses. We discuss the benefits of the non-perturbative action improvement scheme and of the stategy of keeping the lattice spacing (nearly) fixed as the quark mass is varied. We compare our results with other studies and suggest why such a quark mass dependence has not always been seen.Comment: LaTeX. Supercedes our preprint hep-ph/0004180. Version to appear in Phys. Lett.

The string tension in the maximally Abelian gauge after smoothing

We apply smoothing to SU(2) lattice field configurations in 3+1 dimensions before fixing to the maximally Abelian gauge. The Abelian projected string tension is shown to be stable under this, whilst the monopole string tension declines by O(30%). Blocking of the SU(2) fields reduces this effect, but the use of extended monopole definitions does not. We discuss these results in the context of additional confining excitations in the U(1) vacuum.Comment: LATTICE98(confine

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