Asymptotic scaling corrections in QCD with Wilson fermions from the 3-loop average plaquette

We calculate the 3-loop perturbative expansion of the average plaquette in lattice QCD with N_f massive Wilson fermions and gauge group SU(N). The corrections to asymptotic scaling in the corresponding energy scheme are also evaluated. We have also improved the accuracy of the already known pure gluonic results at 2 and 3 loops.Comment: 11 pages and 1 ps figure divided in two sheets; corrected tables V, VI and eq.(19

Three-Loop Results in QCD with Wilson Fermions

We calculate the third coefficient of the lattice beta function in QCD with Wilson fermions, extending the pure gauge results of Luescher and Weisz; we show how this coefficient modifies the scaling function on the lattice. We also calculate the three-loop average plaquette in the presence of Wilson fermions. This allows us to compute the lattice scaling function both in the standard and energy schemes.Comment: 3 pages, LaTeX (fleqn.sty, espcrc2.sty), contribution to Lattice'97. Table caption corrected. The longer write-ups are in hep-lat/9801007 (beta function) and hep-lat/9801003 (plaquette

Topology in QCD with 4 flavours of dynamical fermions

We study the topological properties of full QCD with four flavours of dynamical staggered fermions. In particular the topological susceptibility is measured and the problem of the determination of its first derivative is discussed.Comment: LATTICE99(Topology and Confinement). 3 pages, contains espcrc2.sty fil

Four-loop contributions to long-distance quantities in the two-dimensional nonlinear sigma-model on a square lattice: revised numerical estimates

We give the correct analytic expression of a finite integral appearing in the four-loop computation of the renormalization-group functions for the two-dimensional nonlinear sigma-model on the square lattice with standard action, explaining the origin of a numerical discrepancy. We revise the numerical expressions of Caracciolo and Pelissetto for the perturbative corrections of the susceptibility and of the correlation length. For the values used in Monte Carlo simulations, N=3, 4, 8, the second perturbative correction coefficient of the correlation length varies by 3%, 4%, 3% respectively. Other quantities vary similarly.Comment: 2 pages, Revtex, no figure

Topological properties of full QCD at the phase transition

We investigate the topological properties of the QCD vacuum with 4 flavours of dynamical staggered fermions at finite temperature. To calculate the topological susceptibility we use the field-theoretical method. As in the quenched case, a sharp drop is observed for the topological susceptibility across the phase transition.Comment: LATTICE98(confine

Topological susceptibility in full QCD at zero and finite temperature

We present a study of the topological susceptibility $\chi$ on the lattice for full QCD with 2 and 4 flavours of staggered fermions at zero and finite temperature T. We find that $\chi$ presents a sharp drop across the deconfinement transition. We also study the dependence of $\chi$ on the quark mass at T=0: we have no conclusive evidence for the expected chiral behaviour.Comment: latex source, 8 pages, 4 figure

Analyticity in theta on the lattice and the large volume limit of the topological susceptibility

Non-analyticity of QCD with a \theta term at \theta=0 may signal a spontaneous breaking of both parity and time reversal invariance. We address this issue by investigating the large volume limit of the topological susceptibility $\chi$ in pure SU(3) gauge theory. We obtain an upper bound for the symmetry breaking order parameter and, as a byproduct, the value \chi=(173.4(+/- 0.5)(+/- 1.2)(+1.1 / -0.2) MeV)^4 at \beta=6 (a approx= 0.1 fermi). The errors are the statistical error from our data, the one derived from the value used for \Lambda_L and an estimate of the systematic error respectively.Comment: 15 pages, corrected typos, added 1 reference, minor changes in tex

The spin content of the proton in full QCD

We present preliminary results on the proton spin structure function in full QCD. The measurement has been done using 4 flavours of staggered fermions and an improved definition of the lattice topological charge density.Comment: 3 pages, 3 figures, contribution to Lattice-97. Latex file including espcrc2.sty. The colour of a line in the first figure has been changed to avoid problems on some printer

Topology in SU(2) Yang-Mills theory

New results on the topology of the SU(2) Yang-Mills theory are presented. At zero temperature we obtain the value of the topological susceptibility by using the recently introduced smeared operators as well as a properly renormalized geometric definition. Both determinations are in agreement. At non-zero temperature we study the behaviour of the topological susceptibility across the confinement transition pointing out some qualitative differences with respect to the analogous result for the SU(3) gauge theory.Comment: 3 pages, 4 figures, contribution to Lattice-97. Latex file including espcrc2.st

Analyticity in theta and infinite volume limit of the topological susceptibility in SU(3) gauge theory

The large volume behaviour of the topological susceptibility in SU(3) gauge theory is investigated on the lattice to establish an upper limit on the parity violating terms.Comment: 2 pages, 1 figure, poster presented at Lattice 2004(topology