Gribov ambiguity in gauge theories

Gribov ambiguity in gauge field theories is discussed and it is shown that such an ambiguity exists even for Abelian theories in covariant gauge at finite temperature. Both geometric and algebraic proofs are presented. In view of the importance of non-perturbative methods, some special gauges are given in which such ambiguities do not exist or are not relevant. The significance of these in the study of confinement in QCD is pointed out.     

Covariant quantization of gauge fields without Gribov ambiguity

Recently Parisi and Wu proposed a method of quantizing gauge fields whereby euclidean expectation values are obtained by relaxation to equilibrium of a stochastic process depending on an artificial fifth time parameter. In the present work the equilibrium distribution is determined directly, without reference to the artificial time, by a stationary condition which is an eigenfunction equation in the euclidean Hilbert space. The solution has a perturbative expansion which appears renormalizable by naive power counting. Because of gauge freedom, a free dimensionless gauge parameter appears in the theory although no gauge condition such as ? · A = 0 is imposed.     

Strong-coupling study of the Gribov ambiguity in lattice Landau gauge

We study the strong-coupling limit β=0 of lattice SU(2) Landau gauge Yang–Mills theory. In this limit the lattice spacing is infinite, and thus all momenta in physical units are infinitesimally small. Hence, the infrared behavior can be assessed at sufficiently large lattice momenta. Our results show that at the lattice volumes used here, the Gribov ambiguity has an enormous effect on the ghost propagator in all dimensions. This underlines the severity of the Gribov problem and calls for refined studies also at finite β. In turn, the gluon propagator only mildly depends on the Gribov ambiguity.     

On Gribov ambiguity in finite temperature Abelian gauge theory

It is shown that there is Gribov ambiguity in finite temperature Abelian gauge theory if the gauge theory is defined on the full gauge orbit space. This is demonstrated geometrically and by an explicit construction of solutions to the Gribov equation. Its effects on the evaluation of the temperature-dependent partition function are noted using the Faddeev-Popov procedure.     

Degenerate gauge conditions,generalized Gribov ambiguity and BRST symmetry

The BFV-BRST approach to gauge theories is considered. It is argued that the BRST-invariant boundary conditions ordinarily used do not maintain the necessary degeneracy in the gauge fixing. As a by-product of this discussion, the existence of a generalized Gribov-like ambiguity is suggested. This ambiguity is, however, shown to be just a particular BRST transformation.     

Lorentz gauge and Gribov ambiguity in the compact lattice U(1) theory

The Gribov ambiguity problem is studied for compact U(1) lattice theory within the Lorentz gauge. In the Coulomb phase, it is shown that apart from double Dirac sheets Gribov copies originate mainly from zero-momentum modes of the gauge fields. The removal of the zero-momentum modes is necessary for reaching the absolute maximum of the Lorentz gauge functional.     

Some remarks on the Gribov ambiguity

The set of all connections of a principal bundle over the 4-sphere with compact nonabelian Lie group under the action of the group of gauge transformations is studied. It is shown that no continuous choice of exactly one connection on each orbit can be made. Thus the Gribov ambiguity for the Coloumb gauge will occur in all other gauges. No gauge fixing is possible.     

On the Gribov ambiguity in the Faddeev-Popov procedure

The standard Faddeev-Popov procedure for quantization of a gauge theory is modified so as to be valid even when the Gribov problem is present. The hamiltonian is employed and a definite expression for the path integral is obtained for a wide class of gauges.     

Every gauge orbit passes inside the Gribov horizon

TheL ² topology is introduced on the space of gauge connectionsA and a natural topology is introduced on the group of local gauge transformationsGT. It is shown that the mappingGT×AA defined byAA ^g=g^*Ag+g^*dg is continuous and that each gauge orbit is closed. The Hilbert norm of the gauge connection achieves its absolute minimum on each gauge orbit, at which point the orbit intersects the region bounded by the Gribov horizon.CNR, GNFMResearch supported in part by the National Science Foundation under grant no. PHY 87-15995     

A modification of Faddeev-Popov approach free from Gribov ambiguity

We propose a modified version of the Faddeev-Popov (FP) quantization approach for non-Abelian gauge field theory to avoid Gribov ambiguity. We show that by means of introducing a new method of inserting the correct identity into the Yang-Mills generating functional and considering the identity generated by an integral through a subgroup of the gauge group, the problem of Gribov ambiguity can be removed naturally. Meanwhile by handling the absolute value of the FP determinant with the method introduced by Williams and collaborators, we lift the Jacobian determinant together with the absolute value and obtain a local Lagrangian. The new Lagrangian will have a nilpotent symmetry which can be viewed as an analog of the Becchi-Rouet-Stora-Tyutin symmetry.     

Some aspects of a unified approach to gauge,dual and Gribov theories

We consider quantum chromodynamics (QCD) with N_c colours and N_f flavours. Large N expansions for this theory are discussed and their advantages are pointed out, especially in relation to the possibility of unifying gauge, dual and Gribov theories of strong interactions. We first recall how the 1/N_c expansion of 't Hooft can be related to a dual loop expansion with a fixed coupling constant. We point out the necessity for quarkless (purely gluonic) bound states to appear and their importance in maintaining confinement at higher orders in 1/N_c. We show how non-orientable dual loops are reinterpreted in QCD and how a paradox appears when N_f is such that asymptotic freedom is lost. Some recent results of Cornwall and Tiktopoulos are analyzed in leading order in 1/N_c. We then introduce a 1/N expansion at ? ≡ N_f/N_c fixed and show how it is related to the hadronic topological expansion (TE). This allows an unambiguous definition of reggeon field theory concepts such as the bare pomeron and diffractive dissociation in QDC. We are able to relate the parameter ? to the clustering of hadronic final states into resonances. Decreasing ? corresponds to increasing cluster over gap size. Renormalization of the dual coupling constant as a function of ? is discussed and an apparent paradox is resolved. We are also able to shed some new light on the problem of f extinction in the TE.Finally, we compare our approach to other schemes trying to relate different aspects of hadron physics.     

Absence of the anomalous magnetic moment in a supersymmetric abelian gauge theory

We give a general argument for the vanishing of the anomalous magnetic moment in a supersymmetric Abelian gauge theory recently constructed by Wess and Zumino, provided in such a model the appropriate Ward identities are consistent with renormalized perturbation theory. Our conclusion is in fact confirmed by explicit one-loop calculation, thus providing a new example of cancellation of Feynman graphs in supersymmetric theories.     

Gribov horizon in the presence of dynamical mass generation in Euclidean Yang–Mills theories in the Landau gauge

We find the Goldstino action descending from the N=1 Goldstone–Maxwell superfield action associated with the spontaneous partial supersymmetry breaking, N=2 to N=1, in superspace. The new Goldstino action has higher (second-order) spacetime derivatives, while it can be most compactly described as a solution to the simple recursive relation. Our action seems to be related to the standard (having only the first-order derivatives) Akulov–Volkov action for Goldstino via a field redefinition.     

二次曲线非球面片状样板设计方法的改进

本文以椭圆面为例,对常用的在长轴、短轴上分别加上金属垫片厚度δ形成新的椭圆曲线的设计方法进行了改进,改为保证在顶点及另取的二个控制点处,样板曲线到与零件曲线间的距离等于δ,提高了设计精度,金属垫片长度可由积分求出或用系列弧长仪量出。这种方法也适用于抛物面和双曲面。