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J. Greensite

Publications and source records attributed to J. Greensite.

At least 73 records · Page 4Linked to original sources
arXiv1999

Worldsheet Fluctuations and the Heavy Quark Potential in the AdS/CFT Approach

We consider contributions to the heavy quark potential, in the AdS/CFT approach to SU(N) gauge theory, which arise from first order fluctuations of the associated worldsheet in anti-deSitter space. The gaussian fluctuations occur around a classical worldsheet configuration resembling an infinite square well, with the bottom of the well lying at the AdS horizon. The eigenvalues of the corresponding Laplacian operators can be shown numerically to be very close to those in flat space. We find that two of the transverse world sheet fields become massive, which may have implications for the existence of a L{ü}scher term in the heavy quark potential. It is also suggested that these massive degrees of freedom may relate to extrinsic curvature in an effective D=4 string theory.

hep-th↗
arXiv1999

The Structure of Projected Center Vortices in Lattice Gauge Theory

We investigate the structure of center vortices in maximal center gauge of SU(2) lattice gauge theory at zero and finite temperature. In center projection the vortices (called P-vortices) form connected two dimensional surfaces on the dual four-dimensional lattice. At zero temperature we find, in agreement with the area law behaviour of Wilson loops, that most of the P-vortex plaquettes are parts of a single huge vortex. Small P-vortices, and short-range fluctuations of the large vortex surface, do not contribute to the string tension. All of the huge vortices detected in several thousand field configurations turn out to be unorientable. We determine the Euler characteristic of these surfaces and find that they have a very irregular structure with many handles. At finite temperature P-vortices exist also in the deconfined phase. They form cylindric objects which extend in time direction. After removal of unimportant short range fluctuations they consist only of space-space plaquettes, which is in accordance with the perimeter law behaviour of timelike Wilson loops, and the area law behaviour of spatial Wilson loops in this phase.

hep-lat↗
arXiv1998

Center Projection With and Without Gauge Fixing

We consider projections of SU(2) lattice link variables onto Z(2) center and U(1) subgroups, with and without gauge-fixing. It is shown that in the absence of gauge-fixing, and up to an additive constant, the static quark potential extracted from projected variables agrees exactly with the static quark potential taken from the full link variables; this is an extension of recent arguments by Ambjorn and Greensite, and by Ogilvie. Abelian and center dominance is essentially trivial in this case, and seems of no physical relevance. The situation changes drastically upon gauge fixing. In the case of center projection, there are a series of tests one can carry out, to check if vortices identified in the projected configurations are physical objects. All these criteria are satisfied in maximal center gauge, and we show here that they all fail in the absence of gauge fixing. The non-triviality of center projection is due entirely to the maximal center gauge-fixing, which pumps information about the location of extended physical objects into local Z(2) observables.

hep-lat↗
arXiv1998

Asymptotic Scaling, Casimir Scaling, and Center Vortices

We report on two recent developments in the center vortex theory of confinement: (i) the asymptotic scaling of the vortex density, as measured in Monte Carlo simulations; and (ii) an explanation of Casimir scaling and the adjoint string tension, in terms of the center vortex mechanism.

hep-lat↗
arXiv1998

Evidence for a Center Vortex Origin of the Adjoint String Tension

Wilson loops in the adjoint representation are evaluated on cooled lattices in SU(2) lattice gauge theory. It is found that the string tension of an adjoint Wilson loop vanishes, if the loop is evaluated in a sub-ensemble of configurations in which no center vortex links the loop. This result supports our recent proposal that the adjoint string tension, in the Casimir-scaling regime, can be attributed to a center vortex mechanism.

hep-lat↗
arXiv1998

Remarks on the Heavy Quark Potential in the Supergravity Approach

We point out certain unexpected features of the planar QCD3 confining potential, as computed from a classical worldsheet action in an AdS metric via the Maldacena conjecture. We show that there is no Luscher c/R term in the static-quark potential, which is contrary to both the prediction of various effective string models, and the results of some recent lattice Monte Carlo studies. It is also noted that the glueball masses extracted from classical supergravity tend to finite, coupling-independent constants in the strong coupling limit, even as the string tension tends to infinity in the same limit; this is a counter-intuitive result.

hep-th↗
arXiv1998

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.

hep-lat↗
arXiv1998

Center dominance, Casimir scaling, and confinement in lattice gauge theory

We present numerical evidence that supports the theory of quark confinement based on center vortex condensation. We introduce a special gauge ("maximal center gauge") and center projection, suitable for identification of center vortices. Main focus is then put on the connection of vortices in center projection to "confiners" in full, unprojected gauge-field configurations. Topics briefly discussed include: the relation between vortices and monopoles, first results for SU(3), and the problem of Casimir scaling.

hep-lat↗
arXiv1998

Detection of Center Vortices in the Lattice Yang-Mills Vacuum

We discuss the implementation of the ``direct'' maximal center gauge (a gauge which maximizes the lattice average of the squared-modulus of the trace of link variables), and its use in identifying Z(2) center vortices in Yang-Mills vacuum configurations generated by lattice Monte Carlo. We find that center vortices identified in the vacuum state account for the full asymptotic string tension. Scaling of vortex densities with lattice coupling, change in vortex size with cooling, and sensitivity to Gribov copies is discussed. Preliminary evidence is presented, on small lattices, for center dominance in SU(3) lattice gauge theory.

hep-lat↗
arXiv1997

Casimir Scaling from Center Vortices: Towards an Understanding of the Adjoint String Tension

We argue that the approximate ``Casimir scaling'' of the string tensions of higher-representation Wilson loops is an effect due to the finite thickness of center vortex configurations. It is shown, in the context of a simple model of the Z(2) vortex core, how vortex condensation in Yang-Mills theory can account for both Casimir scaling in intermediate size loops, and color-screening in larger loops. An implication of our model is that the deviations from exact Casimir scaling, which tend to grow with loop size, become much more pronounced as the dimensionality of the group representation increases.

hep-lat↗
arXiv1997

Center Vortices and the Asymptotic String Tension

We present a method for locating center vortices (``fluxons'') in thermalized lattice gauge field configurations. We find evidence, in lattice Monte Carlo simulations, that the asymptotic string tension of fundamental-representation Wilson loops is due to fluctuations in the number of center vortices linking those loops.

hep-lat↗
arXiv1997

Center Dominance, Center Vortices, and Confinement

We present a variety of numerical data supporting the Center Vortex theory of confinement. A method is introduced for identifying the location of center vortices, in thermalized gauge-field configurations generated by lattice Monte Carlo. Fluctuations in the number of such vortices, linked to fundamental representation Wilson loops, appear to be responsible for the asymptotic string tension extracted from those loops.

hep-lat↗
arXiv1996

The Abelianicity of Cooled SU(2) Lattice Configurations

We introduce a gauge-invariant measure of the local "abelianicity" of any given lattice configuration in non-abelian lattice gauge theory; it is essentially a comparison of the magnitude of field strength commutators to the magnitude of the field strength itself. This measure, in conjunction with the cooling technique, is used to probe the SU(2) lattice vacuum for a possible large-scale abelian background, underlying the local short-range field fluctuations. We do, in fact, find a substantial rise in abelianicity over 10 cooling steps or so, after which the abelianicity tends to drop again.

hep-lat↗
arXiv1996

The mass shell of the universe

The classical field equations of general relativity can be expressed as a single geodesic equation, describing the free fall of a point particle in superspace. Based on this formulation, a ``worldline'' quantization of gravity, analogous to the Feynman-Schwinger treatment of particle propagation, is proposed, and a hidden mass-shell parameter is identified. We consider the effective action for the supermetric, which would be induced at one loop. In certain minisuperspace models, we find that this effective action is stationary for vanishing cosmological constant.

gr-qc↗
arXiv1996

Center Dominance and Z2 Vortices in SU(2) Lattice Gauge Theory

We find, in close analogy to abelian dominance in maximal abelian gauge, the phenomenon of center dominance in maximal center gauge for $SU(2)$ lattice gauge theory. Maximal center gauge is a gauge-fixing condition that preserves a residual $Z_2$ gauge symmetry; ``center projection'' is the projection of $SU(2)$ link variables onto $Z_2$ center elements, and ``center dominance'' is the fact that the center-projected link elements carry most of the information about the string tension of the full theory. We present numerical evidence that the thin $Z_2$ vortices of the projected configurations are associated with ``thick'' $Z_2$ vortices in the unprojected configurations. The evidence also suggests that the thick $Z_2$ vortices may play a significant role in the confinement process.

hep-lat↗
arXiv1996

Casimir Scaling vs. Abelian Dominance in QCD String Formation

We show that the hypothesis of abelian dominance in maximal abelian gauge, which is known to work for Wilson loops in the fundamental representation, fails for Wilson loops in higher group representations. Monte Carlo simulations are performed on lattice $SU(2)$ gauge theory, in $D=3$ dimensions, in the maximal abelian gauge, in the confined phase. It is well-known that Creutz ratios extracted from loops in various group representations are proportional to the quadratic Casimir of each representation, in a distance interval from the confinement scale to the point where color screening sets in. In contrast we find numerically, in the same interval, that string tensions extracted from loops built from abelian projected configurations are the same for the fundamental and $j=3/2$ representations, and vanish for the adjoint representation. In addition, we perform a lattice Monte Carlo simulation of the Georgi-Glashow model in $D=3$ dimensions. We find that the representation-dependence of string tensions is that of pure Yang-Mills in the symmetric phase, but changes abruptly to equal tensions for the $j=1/2,~3/2$ representations, and zero tension for $j=1$, at the transition to the Higgs phase. Our results indicate that an effective abelian theory at the confinement scale, invoking {\it only} degrees of freedom (monopoles and photons) associated with a particular Cartan subalgebra, is inadequate to describe the actual interquark potential in an unbroken non-abelian gauge theory.

hep-lat↗
arXiv1995

Deconfinement, Screening and Abelian Projection at Finite Temperature

The behavior of static sources transforming according to different irreducible representations of the gauge group is studied in the context of finite temperature lattice gauge theory. We combine analytical and numerical approaches to extract information about confinement and screening both at low temperatures, and around the deconfinement phase transition. The idea that abelian projection in the Maximally Abelian Gauge reproduces the most important features of confinement and screening is tested at a quantitative level in these finite-T theories. Our results show that while this abelian projection provides correct qualitative features, it fails at a detailed quantitative level.

hep-lat↗