8,492 research outputs found

### Probing Confinement with Chromomagnetic Fields

Using the lattice Schr\"odinger functional we study vacuum dynamics of SU(3)
gauge theory at finite temperature. The vacuum is probed by means of an
external constant Abelian chromomagnetic field. We find that by increasing the
strength of the applied external field the deconfinement temperature decreases
towards zero. This implies that strong enough Abelian chromomagnetic fields
destroy confinement of color.Comment: Lattice2002(topology). 3 pages, 3 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

### 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

### 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

### No Primordial Magnetic Field from Domain Walls

It is pointed out that, contrary to some claims in the literature, the domain
walls cannot be a source of a correlated at large scales primordial magnetic
field, even if the fermionic modes bound on the wall had ferromagnetic
properties. In a particular model with massive (2+1) dimensional fermions bound
to a domain wall, previously claimed to exhibit a ferromagnetic behavior, it is
explicitly shown that the fermionic system in fact has properties of a normal
diamagnetic with the susceptibility vanishing at high temperature.Comment: 8 pages. Modified discussion of the baryon density on an axion domain
wal

### 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

### Long-wavelength excitations of Higgs condensates

Quite independently of the Goldstone phenomenon, recent lattice data suggest
the existence of gap-less modes in the spontaneously broken phase of a $\lambda
\Phi^4$ theory. This result is a direct consequence of the quantum nature of
the `Higgs condensate' that cannot be treated as a purely classical c-number
field.Comment: 6 page

### Dynamical Generation of the Primordial Magnetic Field by Ferromagnetic Domain Walls

The spontaneous generation of uniform magnetic condensate in $QED_3$ gives
rise to ferromagnetic domain walls at the electroweak phase transition. These
ferromagnetic domain walls are caracterized by vanishing effective surface
energy density avoiding, thus, the domain wall problem. Moreover we find that
the domain walls generate a magnetic field $B \simeq 10^{24} Gauss$ at the
electroweak scale which account for the seed field in the so called dynamo
mechanism for the cosmological primordial magnetic field. We find that the
annihilation processes of walls with size $R \simeq 10^5 Km$ could release an
energy of order $10^{52} erg$ indicating the invisible ferromagnetic walls as
possible compact sources of Gamma Ray Bursts.Comment: LaTeX, 8 pages, 1 figur

### 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

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