1,694 research outputs found
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
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
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
Color Dynamics in External Fields
We investigate the vacuum dynamics of U(1), SU(2), and SU(3) lattice gauge
theories in presence of external (chromo)magnetic fields, both in (3+1) and
(2+1) dimensions. We find that the critical coupling for the phase transition
in compact U(1) gauge theory is independent of the strength of an external
magnetic field. On the other hand we find that, both in (3+1) and (2+1)
dimensions, the deconfinement temperature for SU(2) and SU(3) gauge systems in
a constant abelian chromomagnetic field decreases when the strength of the
applied field increases. We conclude that the dependence of the deconfinement
temperature on the strength of an external constant chromomagnetic field is a
peculiar feature of non abelian gauge theories and could be useful to get
insight into color confinement.Comment: 26 pages, 14 figure
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
The phase diagram of QCD with four degenerate quarks
We revisit the determination of the pseudo-critical line of QCD with four
degenerate quarks at non-zero temperature and baryon density by the method of
analytic continuation. We determine the pseudo-critical couplings at imaginary
chemical potentials by high-statistics Monte Carlo simulations and reveal
deviations from the simple quadratic dependence on the chemical potential
visible in earlier works on the same subject. Finally, we discuss the
implications of our findings for the shape of the pseudo-critical line at real
chemical potential, comparing different possible extrapolations.Comment: 8 pages, 8 figures, 2 table
Indications on the Higgs boson mass from lattice simulations
The `triviality' of has been traditionally interpreted within
perturbation theory where the prediction for the Higgs boson mass depends on
the magnitude of the ultraviolet cutoff . 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 can coexist with the limit . 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 GeV, independently of .Comment: 3 pages, 2 figures, Lattice2003(higgs
Probing the non-perturbative dynamics of SU(2) vacuum
The vacuum dynamics of SU(2) lattice gauge theory is studied by means of a
gauge-invariant effective action defined using the lattice Schr\"odinger
functional. Numerical simulations are performed both at zero and finite
temperature. The vacuum is probed using an external constant Abelian
chromomagnetic field. The results suggest that at zero temperature the external
field is screened in the continuum limit. On the other hand at finite
temperature it seems that confinement is restored by increasing the strength of
the applied field.Comment: 29 pages, 10 figures, LaTeX2
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
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