Homology and abelian lattice gauge theories

A simple Abelian model with both Higgs and gauge field degrees of freedom is investigated on a simplicial lattice of arbitrary dimension. We use group character expansion for both fields to get a diagrammatic expansion of the partition function. The diagrams consist of gauge group representation valued 1- and 2-chains. The diagrams are proved to satisfy the constraint that the boundary of the 2-chain representing the gauge field is equal to the 1-chain representing the Higgs field. Otherwise they identically vanish. Simple consequences of this are current conservation and the vanishing of non-null-homologous Wilson loops. Finally we use this picture for giving a lowest order estimate for the critical length of a string. This is the length at which the flux-tube string connecting two opposite charges is likely to break into two pieces due to pair creation.     

Phase transition in one-dimensional lattice gauge theories

Considering one-dimensional nonminimally coupled lattice gauge theories, a class of nonlocal one-dimensional systems is presented which exhibits a phase transition. It is shown that the transition has a latent heat, and therefore is a first-order phase transition.     

Mean field methods for strings and monopoles in abelian lattice gauge theories

Selfconsistent approximations, which join the Bethe-Peierls method and duality transformation, are applied to disorder parameters related to strings (domain boundaries) and monopoles in Z(N) and U(1) lattice gauge theories. The two-phase and the three-phase diagrams are reproduced in three and four dimensions. Nice results are obtained for the internal energy and the monopole charge density. A formulation for gauge theories of the selfconsistent Monte Carlo method is introduced in order to improve these approximations.     

On the nature of the phase transition in a class of lattice gauge theories

We investigate the connection between the phase transition recently found by Anthony in a variant of SU(2) lattice gauge theory and various mechanisms known to produce phase transitions in lattice gauge theories.     

Ultraviolet renormalons in abelian gauge theories

We analyze the large-order behaviour in perturbation theory of classes of diagrams with an arbitrary number of chains (i.e. photon lines, dressed by vacuum polarization insertions). We derive explicit formulae for the leading and subleading divergence as n, the order in perturbation theory, tends to infinity, and a complete result for the vacuum polarization at the next-to-leading order in an expansion in l / N f, where N f is the number of fermion species. In general, diagrams with more chains yield stronger divergence. We define an analogue of the familiar diagrammatic R-operation, which extracts ultraviolet renormalon counterterms as insertions of higher-dimension operators. We then use renormalization group equations to sum the leading (in n/ N f ) k corrections to all orders in l INf and find the asymptotic behaviour in n up to a constant that must be calculated explicitly order by order in 1/N_f.     

On the universality class of the deconfinement transition in lattice gauge theories at finite temperature

We study the (2 + 1)-dimensional Z(2) lattice gauge theory at a finite temperature by Monte Carlo simulation with system size up to three million variables. Our data indicate that the critical exponent β of the Polyakov line correlation function is greater than $\text{1}\text{8}$, in contradiction to a recent conjecture based on renormalization group arguments.     

On the structure of gauge invariant classical observables in lattice gauge theories

For a lattice gauge theory a necessary and sufficient condition on the gauge group is stated, which assures that the linear span of products of Wilson loop observables is dense in the space of continuous, gauge invariant functions on the configuration space. Some groups which fulfill this condition are exhibited, among themU(N) andSU(N),N=1, 2, 3, ... Finally we prove that generically it is fulfilled for all connected, compact Lie groups.     

Functional integration and gauge ambiguities in generalized abelian gauge theories

We consider the covariant quantization of generalized abelian gauge theories on a closed and compact n$n$-dimensional manifold whose space of gauge invariant fields is the abelian group of Cheeger–Simons differential characters. The space of gauge fields is shown to be a non-trivial bundle over the orbits of the subgroup of smooth Cheeger–Simons differential characters. Furthermore each orbit itself has the structure of a bundle over a multi-dimensional torus. As a consequence there is a topological obstruction to the existence of a global gauge fixing condition. A functional integral measure is proposed on the space of gauge fields which takes this problem into account and provides a regularization of the gauge degrees of freedom. For the generalized p$p$-form Maxwell theory closed expressions for all physical observables are obtained. The Green’s functions are shown to be affected by the non-trivial bundle structure. Finally the vacuum expectation values of circle-valued homomorphisms, including the Wilson operator for singular p$p$-cycles of the manifold, are computed and selection rules are derived.     

The deconfinement transition in SU(2) lattice gauge theories

Using Monte Carlo techniques we study the SU(2) Yang-Mills system at finite temperatures for two different forms of lattice action, proposed by Villain and Monton respectively. In both cases the energy density ε exhibits a similar behaviour to the case of the Wilson action, being an order of magnitude smaller at lower temperatures and approaching the Stefan-Boltzmann limit for a free gluon gas at higher temperatures. The transition between these two temperature regimes appears rather abrupt and the specific heat of gluon matter exhibits a sharp peak at the transition point. The transition temperature, expressed in MeV, is found to be consistent in both the cases with that obtained by using the Wilson action, although in the natural units of the corresponding Λ-parameters it differs substantially, being 10.7, 27.3 and 42.8 for Manton, Villain and Wilson actions, respectively.     

On the characterization of the higgs phase in lattice gauge theories

We consider Higgs models on a lattice in 3 or 4 dimensions. Higgs scalars are assumed to transform trivially under a finite subgroup Γ of the compact gauge groupG. We adopt 't Hooft's definition of the Higgs phase, it is characterized by a nonvanishing free energy per unit length (area) of a vortex in 3 (4) dimensions. By using a Peierls argument we show that the models are in the Higgs phase in this sense for suitable coupling constants.     

Chiral gauge theories on the lattice

We propose a method for constructing lattice gauge theories in which fermions transform as a complex representation of the gauge group.     

On-shell improved lattice gauge theories

By means of a spectrum conserving transformation, we show that one of the 3 coefficients in Symanzik's improved action can be chosen freely, if only spectral quantities (masses of stable particles, heavy quark potential etc.) are to be improved. In perturbation theory, the other 2 coefficients are however completely determined and their values are obtained to lowest order.Heisenberg foundation fellow     

Superpropagators for broken supersymmetric abelian gauge theories

By considering an arbitrary globally supersymmetric abelian gauge theory, the most general shifts on the matter and gauge superfields are performed, the superpropagators are derived and employed for discussing the structure of the terms generated into the effective action.     

Optical Abelian lattice gauge theories

We discuss a general framework for the realization of a family of Abelian lattice gauge theories, i.e., link models or gauge magnets, in optical lattices. We analyze the properties of these models that make them suitable for quantum simulations. Within this class, we study in detail the phases of a U(1)$U\left(1\right)$-invariant lattice gauge theory in 2+1$2+1$ dimensions, originally proposed by P. Orland. By using exact diagonalization, we extract the low-energy states for small lattices, up to 4×4$4\times 4$. We confirm that the model has two phases, with the confined entangled one characterized by strings wrapping around the whole lattice. We explain how to study larger lattices by using either tensor network techniques or digital quantum simulations with Rydberg atoms loaded in optical lattices, where we discuss in detail a protocol for the preparation of the ground-state. We propose two key experimental tests that can be used as smoking gun of the proper implementation of a gauge theory in optical lattices. These tests consist in verifying the absence of spontaneous (gauge) symmetry breaking of the ground-state and the presence of charge confinement. We also comment on the relation between standard compact U(1)$U\left(1\right)$ lattice gauge theory and the model considered in this paper.     

Recent advances in lattice gauge theories

Recent progress in the field of lattice gauge theories is briefly reviewed for a nonspecialist audience. While the emphasis is on the latest and more definitive results that have emerged prior to this symposium, an effort has been made to provide them with minimal technicalities.