Unstable Modes and Confinement in the Lattice Schr\"odinger Functional Approach

We analyze the problem of the Nielsen-Olesen unstable modes in the SU(2) lattice gauge theory by means of a recently introduced gauge-invariant effective action. We perform numerical simulations in the case of a constant Abelian chromomagnetic field. We find that for lattice sizes above a certain critical length the density of effective action shows a behaviour compatible with the presence of the unstable modes. We put out a possible relation between the dynamics of the unstable modes and the confinement.Comment: 15 pages, LaTeX2e file, 5 figure

Indications on the Higgs boson mass from lattice simulations

The `triviality' of $\Phi^4_4$ has been traditionally interpreted within perturbation theory where the prediction for the Higgs boson mass depends on the magnitude of the ultraviolet cutoff $\Lambda$. This approach crucially assumes that the vacuum field and its quantum fluctuations rescale in the same way. The results of the present lattice simulation, confirming previous numerical indications, show that this assumption is not true. As a consequence, large values of the Higgs mass $m_H$ can coexist with the limit $\Lambda\to \infty$. As an example, by extrapolating to the Standard Model our results obtained in the Ising limit of the one-component theory, one can obtain a value as large as $m_H=760 \pm 21$ GeV, independently of $\Lambda$.Comment: 3 pages, 2 figures, Lattice2003(higgs

Exploring the Dynamics of Three-Dimensional Lattice Gauge Theories by External Fields

We investigate the dynamics of three-dimensional lattice gauge theories by means of an external Abelian magnetic field. For the SU(2) lattice gauge theory we find evidence of the unstable modes.Comment: 3 pages, PostScript. Contribution to the LATTICE 93 Conference (Dallas, U.S.A., September 1993) preprint BARI-TH-162/9

Generalized Gaussian Effective Potential: Low Dimensional Scalar Fields

We study a generalization of the Gaussian effective potential for self-interacting scalar fields in one and two spatial dimensions. We compute the two-loop corrections and discuss the renormalization of the generalized Gaussian effective potential.Comment: tex, 10 pages + 4 Postscript figures include

On the Meissner effect in SU(2) lattice gauge theory

We investigate the dual superconductor model of color confinement in SU(2) lattice gauge theory. We find that the transverse distribution of the longitudinal chromoelectric field between static quarks displays the dual Meissner effect. We also give evidence that the problem of color confinement could be approached in the framework of the 't~Hooft's Abelian projection.Comment: 3 pages, PostScript. Contribution to the LATTICE 93 Conference (Dallas, U.S.A., September 1993) preprint BARI-TH-161/9

Investigations on the deconfining phase transition in QCD

We investigate the deconfining phase transition in SU(3) pure gauge theory and in full QCD with two flavors of staggered fermions by means of a gauge invariant thermal partition functional. In the pure gauge case our finite size scaling analysis is in agreement with the well known weak first order phase transition. In the case of 2 flavors full QCD we find that the phase transition is consistent with weak first order, contrary to the expectation of a crossover for not too large quark masses.Comment: 3 pages, 3 figures, Lattice2003(topology

QCD dynamics in a constant chromomagnetic field

We investigate the phase transition in full QCD with two flavors of staggered fermions in presence of a constant abelian chromomagnetic field. We find that the critical temperature depends on the strength of the chromomagnetic field and that the deconfined phase extends to very low temperatures for strong enough fields. As in the case of zero external field, a single transition is detected, within statistical uncertainties, where both deconfinement and chiral symmetry restoration take place. We also find that the chiral condensate increases with the strength of the chromomagnetic field.Comment: 18 pages, 8 figures, 1 tabl