S. P. Sorella

Refinement of the Gribov-Zwanziger approach in the Landau gauge: Infrared propagators in harmony with the lattice results

Recent lattice data have reported an infrared suppressed, positivity violating gluon propagator which is nonvanishing at zero momentum and a ghost propagator which is no longer enhanced. This paper discusses how to obtain analytical results which are in qualitative agreement with these lattice data within the Gribov-Zwanziger framework. This framework allows one to take into account effects related to the existence of gauge copies, by restricting the domain of integration in the path integral to the Gribov region. We elaborate to great extent on a previous short paper by presenting additional results, also confirmed by the numerical simulations. A detailed discussion on the soft breaking of the Becchi-Rouet-Stora-Tyutin symmetry arising in the Gribov-Zwanziger approach is provided.

Algebraic renormalization : perturbative renormalization, symmetries and anomalies

This text provides a pedagogical and self-contained introduction to the algebraic method of renormalization in perturbative quantum field theory. This method is based on general theorems of renormalization, in particular on the Quantum Action Principle. It allows one to treat the problems of the renormalizability and the anomalies of models with local or global symmetries in terms of algebraic properties of classical field polynomials. Several examples (for instance topological models) are considered in some detail. One of the main advantages of this method, beyond its simplicity, is its great power, because no particular subtraction or regularization scheme preserving the symmetries of the problem is a priori required.

Dynamical origin of the refinement of the Gribov-Zwanziger theory

In recent years, the Gribov-Zwanziger action was refined by taking into account certain dimension 2 condensates. In this fashion, one succeeded in bringing the gluon and the ghost propagator obtained from the Gribov-Zwanziger model in qualitative and quantitative agreement with the lattice data. In this paper, we shall elaborate further on this aspect. First, we shall show that more dimension 2 condensates can be taken into account than considered so far and, in addition, we shall give firm evidence that these condensates are in fact present by discussing the effective potential. It follows thus that the Gribov-Zwanziger action dynamically transforms itself into the refined version, thereby showing that the continuum nonperturbative Landau gauge fixing, as implemented by the Gribov-Zwanziger approach, is consistent with lattice simulations.

Remarks on a class of renormalizable interpolating gauges

A class of covariant gauges allowing one to interpolate between the Landau, the maximal abelian, the linear covariant and the Curci-Ferrari gauges is discussed. Multiplicative renormalizability is proven to all orders by means of algebraic renormalization. All one-loop anomalous dimensions of the fields and gauge parameters are explicitly evaluated in the scheme.

Soft breaking of BRST invariance for introducing non-perturbative infrared effects in a local and renormalizable way

Abstract The possibility of introducing non-perturbative infrared effects leading to a modification of the long distance behavior of gauge theories through a soft breaking of the BRST invariance is investigated. The method reproduces the Gribov–Zwanziger action describing the restriction of the domain of integration in the Feynman path integral to the Gribov region and a model for the dynamical quark mass generation is presented. The soft symmetry breaking relies on the introduction of BRST doublets and massive physical parameters, which allow one to distinguish the infrared region from the ultraviolet one, within the same theory.

Glueball Masses from an Infrared Moment Problem

We set up an infrared-based moment problem to obtain estimates of the masses of the scalar, pseudoscalar, and tensor glueballs in Euclidean Yang-Mills theories using the refined Gribov-Zwanziger (RGZ) version of the Landau gauge, which takes into account nonperturbative physics related to gauge copies. Employing lattice input for the mass scales of the RGZ gluon propagator, the lowest order moment problem approximation gives the values m(0++) ≈ 1.96 GeV, m(2++) ≈ 2.04 GeV, and m(0-+) ≈ 2.19 GeV in the SU(3) case, all within a 20% range of the corresponding lattice values. We also recover the mass hierarchy m(0++) < m(2++) < m(0-+).

Gribov no-pole condition, Zwanziger horizon function, Kugo-Ojima confinement criterion, boundary conditions, BRST breaking and all that

We aim to offer a kind of unifying view on two popular topics in the studies of nonperturbative aspects of Yang-Mills theories in the Landau gauge: the so-called Gribov-Zwanziger approach and the Kugo-Ojima confinement criterion. Borrowing results from statistical thermodynamics, we show that imposing the Kugo-Ojima confinement criterion as a boundary condition leads to a modified yet renormalizable partition function. We verify that the resulting partition function is equivalent with the one obtained by Gribov and Zwanziger, which restricts the domain of integration in the path integral within the first Gribov horizon. The construction of an action implementing a boundary condition allows one to discuss the symmetries of the system in the presence of the boundary. In particular, the conventional Becchi-Rouet-Stora-Tyutin symmetry is softly broken.

Renormalization and finiteness of topological BF theories

We show that the BF theory in any space-time dimension, when quantized in a certain linear covariant gauge, possesses a vector supersymmetry. The generator of the latter together with those of the BRS transformations and of the translations form the basis of a superalgebra of the Wess-Zumino type. We give a general classification of all possible anomalies and invariant counterterms. Their absence, which amounts to ultraviolet finiteness, follows from purely algebraic arguments in the lower-dimensional cases.

Gribov horizon and BRST symmetry: A few remarks

The issue of the Becchi-Rouet-Stora-Tyutin (BRST) symmetry in the presence of the Gribov horizon is addressed in Euclidean Yang-Mills theories in the Landau gauge. The positivity of the Faddeev-Popov operator within the Gribov region enables us to convert the soft breaking of the BRST invariance exhibited by the Gribov-Zwanziger action into a nonlocal exact symmetry, displaying explicit dependence from the nonperturbative Gribov parameter. Despite its nonlocality, this symmetry turns out to be useful in order to establish nonperturbative Ward identities, allowing us to evaluate the vacuum expectation value of quantities which are BRST exact. These results are generalized to the refined Gribov-Zwanziger action introduced in Dudal et al. [Phys. Rev. D 77, 071501 (2008)], which yields a gluon propagator which is nonvanishing at the origin in momentum space, and a ghost propagator which is not enhanced in the infrared.

A study of the Gribov copies in linear covariant gauges in euclidean Yang-Mills theories

The Gribov copies and their consequences on the infrared behavior of the gluon propagator are investigated in euclidean Yang-Mills theories quantized in linear covariant gauges. Considering small values of the gauge parameter, it turns out that the transverse component of the gluon propagator is suppressed, while its longitudinal part is left unchanged. A Green function, tr(k), which displays infrared enhancement and which reduces to the ghost propagator in the Landau gauge is identified. The inclusion of the dimension two gluon condensate Aμ2 is also considered. In this case, the transverse component of the gluon propagator and the Green function tr(k) remain suppressed and enhanced, respectively. Moreover, the longitudinal part of the gluon propagator becomes suppressed. A comparison with the results obtained from the studies of the Schwinger-Dyson equations and from lattice simulations is provided.