418 research outputs found

### Scaling properties of Wilson loops pierced by P-vortices

P-vortices, in an SU(N) lattice gauge theory, are excitations on the
center-projected Z(N) lattice. We study the ratio of expectation values of
SU(2) Wilson loops, on the unprojected lattice, linked to a single P-vortex, to
that of Wilson loops which are not linked to any P-vortices. When these ratios
are plotted versus loop area in physical units, for a range of lattice
couplings, it is found that the points fall approximately on a single curve,
consistent with scaling. We also find that the ratios are rather insensitive to
the point where the minimal area of the loop is pierced by the P-vortex.Comment: 4 pages, 4 figure

### Dynamical Origin of the Lorentzian Signature of Spacetime

It is suggested that not only the curvature, but also the signature of
spacetime is subject to quantum fluctuations. A generalized D-dimensional
spacetime metric of the form $g_{\mu \nu}=e^a_\mu \eta_{ab} e^b_\nu$ is
introduced, where $\eta_{ab} = diag\{e^{i\theta},1,...,1\}$. The corresponding
functional integral for quantized fields then interpolates from a Euclidean
path integral in Euclidean space, at $\theta=0$, to a Feynman path integral in
Minkowski space, at $\theta=\pi$. Treating the phase $e^{i\theta}$ as just
another quantized field, the signature of spacetime is determined dynamically
by its expectation value. The complex-valued effective potential $V(\theta)$
for the phase field, induced by massless fields at one-loop, is considered. It
is argued that $Re[V(\theta)]$ is minimized and $Im[V(\theta)]$ is stationary,
uniquely in D=4 dimensions, at $\theta=\pi$, which suggests a dynamical origin
for the Lorentzian signature of spacetime.Comment: 6 pages, LaTe

### Charge Screening, Large-N, and the Abelian Projection Model of Confinement

We point out that the abelian projection theory of quark confinement is in
conflict with certain large-N predictions. According to both large-N and
lattice strong-coupling arguments, the perimeter law behavior of adjoint Wilson
loops at large scales is due to charge-screening, and is suppressed relative to
the area term by a factor of $1/N^2$. In the abelian projection theory,
however, the perimeter law is due to the fact that $N-1$ out of $N^2-1$ adjoint
quark degrees of freedom are (abelian) neutral and unconfined; the suppression
factor relative to the area law is thus only $1/N$. We study numerically the
behavior of Wilson loops and Polyakov lines with insertions of (abelian) charge
projection operators, in maximal abelian gauge. It appears from our data that
the forces between abelian charged, and abelian neutral adjoint quarks are not
significantly different. We also show via the lattice strong-coupling expansion
that, at least at strong couplings, QCD flux tubes attract one another, whereas
vortices in type II superconductors repel.Comment: 20 pages (Latex), 8 figures, IFUP-TH 54/9

### Center Disorder in the 3D Georgi-Glashow Model

We present a number of arguments relating magnetic disorder to center
disorder, in pure Yang-Mills theory in D=3 and D=4 dimensions. In the case of
the D=3 Georgi-Glashow model, we point out that the abelian field distribution
is not adequatedly represented, at very large scales, by that of a monopole
Coulomb gas. The onset of center disorder is associated with the breakdown of
the Coulomb gas approximation; this scale is pushed off to infinity in the
QED_3 limit of the 3D Georgi-Glashow model, but should approach the
color-screening length in the pure Yang-Mills limit.Comment: 22 pages including 3 figures, Latex2

### Constituent Gluon Content of the Static Quark-Antiquark State in Coulomb Gauge

Motivated by the gluon-chain model of flux tube formation, we compute and
diagonalize the transfer matrix in lattice SU(2) gauge theory for states
containing heavy static quark-antiquark sources, with separations up to one
fermi. The elements of the transfer matrix are calculated by variational Monte
Carlo methods, in a basis of states obtained by acting on the vacuum state with
zero, one, and two-gluon operators in Coulomb gauge. The color Coulomb
potential is obtained from the zero gluon to zero gluon element of the transfer
matrix, and it is well-known that while this potential is asymptotically
linear, it has a slope which is two to three times larger than the standard
asymptotic string tension. We show that the addition of one and two gluon
states results in a potential which is still linear, but the disagreement with
the standard asymptotic string tension is reduced to 38% at the largest lattice
coupling we have studied

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