On the Migdal-Makeenko Equation for Simple and Nonsimple Contours

The Migdal-Makeenko equation differs explicitely in the abelian and nonabelian case for simple smooth contours already. This is due to endpoint singularities of gauge noninvariant functionals which appear in the nonabelian equation providing anomalous finite contributions in the course of renormalization. Corresponding results are discussed for nonsimple contours.     

Braces and the Yang–Baxter Equation

Several aspects of relations between braces and non-degenerate involutive set-theoretic solutions of the Yang–Baxter equation are discussed and many consequences are derived. In particular, for each positive integer n a finite square-free multipermutation solution of the Yang–Baxter equation with multipermutation level n and an abelian involutive Yang–Baxter group is constructed. This answers a problem of Gateva-Ivanova and Cameron. It is proved that finite non-degenerate involutive set-theoretic solutions of the Yang–Baxter equation whose associated involutive Yang–Baxter group is abelian are multipermutation solutions. Earlier the authors proved this with the additional square-free hypothesis on the solutions. It is also proved that finite square-free non-degenerate involutive set-theoretic solutions associated to a left brace are multipermutation solutions.     

A no-go theorem for the nonabelian topological mass mechanism in four dimensions

We prove that there is no power-counting renormalizable nonabelian generalization of the abelian topological mass mechanism in four dimensions. The argument is based on the technique of consistent deformations of the master equation developed by G. Barnich and one of the authors. Recent attempts involving extra fields are also commented upon.     

Steady state and relaxation spectrum of the Oslo rice-pile model

We show that the one-dimensional Oslo rice-pile model is a special case of the abelian distributed processors model. The exact steady state of the model is determined. We show that the time evolution operator for the system satisfies the equation where n=L(L+1)/2 for a pile with L sites. This implies that has only one eigenvalue 1 corresponding to the steady state, and all other eigenvalues are exactly zero. Also, all connected time-dependent correlation functions in the steady state of the pile are exactly zero for time difference greater than n. Generalization to other abelian critical height models where the critical thresholds are randomly reset after each toppling is briefly discussed.     

Vortices as Degenerate Metrics

We note that the Bogomolny equation for abelian vortices is precisely the condition for invariance of the Hermitian–Einstein equation under a degenerate conformal transformation. This leads to a natural interpretation of vortices as degenerate Hermitian metrics that satisfy a certain curvature equation. Using this viewpoint, we rephrase standard results about vortices and make new observations. We note the existence of a conceptually simple, non-linear rule for superposing vortex solutions, and we describe the natural behaviour of the L ²-metric on the moduli space upon restriction to a class of submanifolds.     

Four‐dimensional couplings among BF and matter theories from BRST cohomology

The local and manifestly covariant Lagrangian interactions in four spacetime dimensions that can be added to a “free” model that describes a generic matter theory and an abelian BF theory are constructed by means of deforming the solution to the master equation on behalf of specific cohomological techniques.     

Some non-abelian phase spaces in low dimensions

A non-abelian phase space, or a phase space of a Lie algebra, is a generalization of the usual (abelian) phase space of a vector space. It corresponds to a para-Kähler structure in geometry. Its structure can be interpreted in terms of left-symmetric algebras. In particular, a solution of an algebraic equation in a left-symmetric algebra which is an analogue of classical Yang–Baxter equation in a Lie algebra can induce a phase space. In this paper, we find that such phase spaces have a symplectically isomorphic property. We also give all such phase spaces in dimension 4 and some examples in dimension 6. These examples can be a guide for a further development.     

Rigid invariance as derived from BRS invariance: the abelian Higgs model

Consequences of a symmetry, e.g. relations amongst Green functions, are renormalization scheme independently expressed in terms of a rigid Ward identity. The corresponding local version yields information on the respective current. In the case of spontaneous breakdown one has to define the theory via the BRS invariance and thus to construct rigid and current Ward identity nontrivially in accordance with it. We performed this construction to all orders of perturbation theory in the abelian Higgs model as a prelude to the standard model. A technical tool of interest in itself is the use of a doublet of external scalar “background” fields. The Callan-Symanzik equation has an interesting form and follows easily once the rigid invariance is established.     

The average action for scalar fields near phase transitions

We compute the average action for scalar fields in two, three and four dimensions, including the effects of wave function renormalization. A study of the one loop evolution equations for the scale dependence of the average action gives a unified picture of the qualitatively different behaviour in various dimensions for discrete as well as abelian and nonabelian continuous symmetry. The different phases and the phase transitions can be infered from the evolution equation.     

Källen's theorem and the unphysical nature of abelian external fields in Yang-Mills theory

Yang-Mills theory is considered in an abelian external field with a covariant background gauge-fixing condition. The failure mechanism of Källen's inequality for the charge renormalization constant is studied, and indicates that a uniform external electric field should decay predominantly into negative norm gluon ghost states. Explicit calculation verifies this conjecture. This result is interpreted as evidence of the unphysical nature of abelian field configurations in Yang-Mills quantum theory.     

Conformal Orbifold Theories and Braided Crossed G-Categories

The Berezin-Toeplitz deformation quantization of an abelian variety is explicitly computed by the use of Theta-functions. An SL(2n,)-equivariant complex structure dependent equivalence E between the constant Moyal-Weyl product and this family of deformations is given. This equivalence is seen to be convergent on the dense subspace spanned by the pure phase functions. The Toeplitz operators associated to the equivalence E applied to a pure phase function produces a covariant constant section of the endomorphism bundle of the vector bundle of Theta-functions (for each level) over the moduli space of abelian varieties.Applying this to any holonomy function on the symplectic torus one obtains as the moduli space of U(1)-connections on a surface, we provide an explicit geometric construction of the abelian TQFT-operator associated to a simple closed curve on the surface. Using these TQFT-operators we prove an analog of asymptotic faithfulness (see [A1]) in this abelian case. Namely that the intersection of the kernels for the quantum representations is the Toreilli subgroup in this abelian case.Furthermore, we relate this construction to the deformation quantization of the moduli spaces of flat connections constructed in [AMR1] and [AMR2]. In particular we prove that this topologically defined *-product in this abelian case is the Moyal-Weyl product. Finally we combine all of this to give a geometric construction of the abelian TQFT operator associated to any link in the cylinder over the surface and we show the glueing axiom for these operators.This research was conducted in part for the Clay Mathematics Institute at University of California, Berkeley.This work was supported by MaPhySto – A Network in Mathematical Physics and Stochastics, funded by The Danish National Research Foundation     

Roots for quantum ergodic theory invon Neumann's work

In ergodic theory von Neumann emphasized the spectral analysis of the unitary implementor and the possibility to express point translations as automorphisms over abelian algebras. Replacing the abelian algebras by noncommutative algebras good ergodic behaviour asks for type II and III algebras. The possibility for existing K-systems and Anosov systems in this framework is discussed. Von Neumnns example of a type III algebra is examined from this viewpoint.     

General structure of nonlinear evolution equations in 1+2 dimensions integrable by the two-dimensional Gelfand-Dickey-Zakharov-Shabat spectral problem and their transformation properties

The general form of nonlinear evolution equations connected with the matrix two-dimensional Gelfand-Dickey-Zakharov-Shabat spectral problem is found. The infinite-dimensional abelian group of general Bäcklund transformations and infinite-dimensional abelian symmetry group for these equations are constructed.     

Bounds on the decay of correlations for λ(∇φ)4 models

We consider models, with an abelian continuous group of symmetry, of the type: $$H = \sum\limits_x {\left[ {\frac{1}{2}(\nabla _x \phi )^2 + \frac{\lambda }{4}(\nabla _x \phi )^4 } \right].}$$ We generalize Brascamp-Lieb inequalities to get (λ-independent) bounds on the low momentum behaviour of general correlation functions when these are truncated into two clusters. We then use this result to derive an asymptotic expansion (up the second order in λ) of the dielectric constant of this system.     

Equivariant Holonomy for Bundles and Abelian Gerbes

This paper generalizes Bismut’s equivariant Chern character to the setting of abelian gerbes. In particular, associated to an abelian gerbe with connection, an equivariantly closed differential form is constructed on the space of maps of a torus into the manifold. These constructions are made explicit using a new local version of the higher Hochschild complex, resulting in differential forms given by iterated integrals. Connections to two dimensional topological field theories are indicated. Similarly, this local higher Hochschild complex is used to calculate the 2-holonomy of an abelian gerbe along any closed oriented surface, as well as the derivative of 2-holonomy, which in the case of a torus fits into a sequence of higher holonomies and their differentials.     

Quantization of chiral gauge theories in two-dimensions

It is shown that both abelian and non abelian chiral gauge theories in two dimensions can be made gauge invariant at the quantum level by adding a scalar field. In the bosonized form of the theory, the scalar field appears in a gauged Wess-Zumino action. The current algebra of the extended abelian theory is shown to be free of anomalous terms.     

Green functions of vortex operators

We study the euclidean Green functions of the 't Hooft vortex operator, primarily for abelian gauge theories. The operator is written in terms of elementary fields, with emphasis on a form in which it appears as the exponential of a surface integral. We explore the requirement that the Green functions depend only on the boundary of this surface. The Dirac veto problem appears in a new guise. We present a two-dimensional “solvable model” of a Dirac string, which suggests a new solution of the veto problem. The renormalization of the Green functions of the abelian Wilson loop and abelian vortex operator is studied with the aid of the operator product expansion. In each case, an overall multiplication of the operator makes all Green functions finite; a surprising cancellation of divergences occurs with the vortex operator. We present a brief discussion of the relation between the nature of the vacuum and the cluster properties of the Green functions of the Wilson and vortex operators, for a general gauge theory. The surface-like cluster property of the vortex operator in an abelian Higgs theory is explored in more detail.     

On the invertible objects in tensor categories

The invertible objects in a tensor category form a subcategory the Grothendieck ring of which is the group ring of an abelian group. This abelian fusion ring acts on the objects of the initial category and one can in principle determine all 6j-symbols that contain the lable of an invertible object. Received 1st October 2001 / Received in final form 12 April 2002 Published online 2 October 2002 RID="a" ID="a"e-mail: ganchev@inrne.bas.bg     

Stability properties and the KMS condition

First we derive stability properties of KMS states and subsequently we derive the KMS condition from stability properties. New results include a convergent perturbation expansion for perturbed KMS states in terms of appropriate truncated functions and stability properties of ground states. Finally we extend the results of Haag, Kastler, Trych-Pohlmeyer by proving that stable states ofL ¹-asymptotically abelian systems which satisfy a weak three point cluster property are automatically KMS states. This last theorem gives an almost complete characterization of KMS states, ofL ¹-asymptotic abelian systems, by stability and cluster properties (a slight discrepancy can occur for infinite temperature states).Supported during this research by the Norwegian Research Council for Science and Humanities