The Non-Perturbative Approach to the Infrared Problem in QCD at Finite Temperature

A non-perturbative approach is developed for investigation of the infrared problem in QCD at T ≠ 0 in the ghost-free axial gauge. The problem is solved by using a 3-dimensional theory within the exact Slavnov-Taylor identities and Schwinger-Dyson equations. The system of two non-linear integral equations for the structural functions of the gluon polarization tensor is obtained whose solution determines the infrared behavior of the temperature Green functions in the 4-dimensional QCD. The simplest solution of these equations which is the same as the first term of the perturbation expansion shows the presence of singularities in the gluon propagator at momenta p ∼ g²T, that cannot be eliminated by any choice of the gauge. The infrared instability of QCD at T ≠ 0 caused by these singularities is discussed.     

Renormalization Proof for Spontaneously Broken Yang–Mills Theory with Flow Equations

In this paper we present a renormalizability proof for spontaneously broken SU(2) gauge theory. It is based on Flow Equations, i.e. on the Wilson renormalization group adapted to perturbation theory. The power counting part of the proof, which is conceptually and technically simple, follows the same lines as that for any other renormalizable theory. The main difficulty stems from the fact that the regularization violates gauge invariance. We prove that there exists a class of renormalization conditions such that the renormalized Green functions satisfy the Slavnov-Taylor identities of SU(2) Yang-Mills theory on which the gauge invariance of the renormalized theory is based.     

Generalized Slavnov-Taylor,BRST and covariance identities from the geometry of the gauge surface

It is shown that various Green function identities in quantized gauge theories may be viewed as arising from the local conformal groupSO(N+1, 1) of motions of theN-dimensional gauge fixing surface. Translations and rotations correspond respectively to the usual Slavnov-Taylorinvariance and anew ‘dual’ analogue. Dilations give rise to thecovariance identities, and in axial type gauges we obtain a closed form for the covariance relationships. It is shown that the generalized Slavnov-Taylor identities, and the BRST identities, are equivalent, as are their duals.     

Wilson renormalization group formulation of real time thermal field theories

We apply Renormalization Group techniques to the Real Time formulation of thermal field theory. Due to the separation between the T = 0 and the T ≠ 0 parts of the propagator in this formalism, one can derive exact evolution equations for the Green functions describing the effect of integrating out thermal fluctuations of increasing wavelengths, the initial conditions being the renormalized Green functions of the T = 0 theory. As a first application, we study the phase transition for the real scalar theory, computing the order of the transition, the critical temperature, and critical exponents, in different approximations to the evolution equations for the scalar potential.     

On the 1-Loop Renormalization of the Electroweak Standard Model and its Application to Leptonic Processes

A renormalization scheme for the electroweak standard model is presented in which the electric charge and the masses of the gauge bosons, Higgs particle and fermions are used as physical parameters. The photon is treated such that quantum electrodynamics is contained as a simple substructure. Field renormalization respecting the gauge symmetry gives finite propagators and vertex functions. The Ward identities between the Green functions of the unphysical sector allow a renormalization that maintains the simple pole structure of the propagators in the t'Hooft-Feynman gauge. We give a complete list of self energies and all renormalization constants also in the unphysical Higgs and ghost sector. Explicit results are given for the renormalized self energies, vertex functions and boxes that enter the evaluation of 1-loop radiative corrections to fermionic processes. We calculate the 1-loop radiative corrections to purely leptonic reactions like μ decay, vμ_μe scattering and μ pair production in e⁺e⁻annihilation. A test of the standard model is performed by comparing these low energy data with the results of the PP collider experiments for the W and Z boson masses.     

BRS symmetry for Yang-Mills theory with exact renormalization group

In the exact renormalization-group (RG) flow in the infrared cutoff Λ one needs boundary conditions. In a previous paper on SU(2) Yang-Mills theory we proposed to use the nine physical relevant couplings of the effective action as boundary conditions at the physical point Λ= 0 (these couplings are defined at some non-vanishing subtraction point μ≠ 0). In this paper we show perturbatively that it is possible to appropriately fix these couplings in such a way that the full set of Slavnov-Taylor (ST) identities are satisfied. Three couplings are given by the vector and ghost wave-function normalization and the three-vector coupling at the subtraction point; three of the remaining six are vanishing (e.g. the vector mass) and the others are expressed by irrelevant vertices evaluated at the subtraction point. We follow the method used by Becchi to prove ST identities in the RG framework. There the boundary conditions are given at a non-physical point Λ = Λ′ ≠ 0, so that one avoids the need of a non-vanishing subtraction point.     

On the cancellation of hard anomalies in gauge field models: a regularization independent proof

In this paper we prove Bardeen's conjecture that the anomaly of the Adler-Bardeen-Bell-Jackiw-Schwinger type in gauge models are definitely absent if they are cancelled at the first order of the perturbation expansion. Our analysis develops within the regularization independent B.P.H.Z. renormalization scheme. We discuss the possible appearance of anomalies in an enlarged class of gauge models admitting soft violations of the Slavnov-Taylor identities which prescribe the gauge transformation properties of the Green functions. By a repeated use of the Callan-Symanzik equation we conclude that the lowest non vanishing contributions to the anomalies must necessarily correspond to the first order in the perturbation expansion, hence if they are cancelled at this order the theory will be definitely anomaly free.     

Renormalizability proof for QED based on flow equations

We prove the perturbative renormalizability of Euclidean QED₄ using flow equations, i.e. with the aid of the Wilson renormalization group adapted to perturbation theory. As compared to ₄ ⁴ the additional difficulty to overcome is that the regularization violates gauge invariance. We prove that there exists a class of renormalization conditions such that the renormalized Green functions satisfy the QED Ward identities and such that they are infrared finite at nonexceptional momenta. We give bounds on the singular behaviour at exceptional momenta (due to the massless photon) and comment on the adaptation to the case when the fermions are also massless.Supported by the Swiss National Science Foundation and by the Ambrose Monell Foundation.     

An extension of the nonsymmetric unified field theory

The field equations, in the new formulation of Einstein's unified field theory, are extended from the present vacuum form to the general case in which sources are present. In this generalization the contracted torsion tensor corresponds to the electromagnetic four-potential. By this correspondence, Einsteins-gauge transformation becomes identical to the ordinary electromagnetic gauge symmetry. The generalized Bianchi identities are found and used to discuss deviations from the Einstein-Lorentz equations of motion.     

Conformal gauges and renormalized equations of motion in massless quantum electrodynamics

A formulation of massless QED is studied with a non-singular Lagrangian and conformal invariant equations of motion. It makes use of non-decomposable representations of the conformal groupG and involves two dimensionless scalar fields (in addition to the conventional charged field and electromagnetic potential) but gauge invariant Green functions are shown to coincide with those of standard (massless) QED. Assuming that the (non-elementary) representation ofG for the 5-potential which leaves the equations of motion invariant and leads to the free photon propagator of Johnson-Baker-Adler (JBA) conformal QED remains unaltered by renormalization, we prove that consistency requirements for conformal invariant 2-, 3-, and 4-point Green functions satisfying (renormalized) equations of motion and standard Ward identities lead to either a trivial solution (withe=0) or to a subcanonical dimensiond=1/2 for the charged field.To the memory of Kurt Symanzik     

Gauge Symmetry and Transverse Symmetry Transformations in Gauge Theories

The transverse symmetry transformations associated with the normal symmetry transformations are proposed to build the transverse constraints on the basic vertices in gauge theories. I show that, while the BRST symmetry in non-Abelian gauge theory QCD (Quantum Chromodynamics) leads to the Slavnov-Taylor identity for the quark-gluon vertex which constrains the longitudinal part of thevertex, the transverse symmetry transformation associated with the BRST symmetry enables to derive the transverse Slavnov-Taylor identity for the quark-gluon vertex, which constrains the transverse part of the quark-gluon vertex from the gauge symmetry of QCD.     

INFRARED BEHAVIOR OF THE RUNNING COUPLING CONSTANT IN QCD

The infrared behavior of the running coupling constant in QCD has been studied using the Schwinger-Dyson equation of the gluon propagator based on the Slavnov-Taylor identities in axial gauge. It is shown that the infrared running coupling constant behavior g^-2(Q²)=g²(μ²/Q²) in the infrared limit Q²/μ²→0.     

Collective excitations of massive Dirac particles in a hot and dense medium

The one-loop dispersion relation which defines the collective excitations of massive Dirac particles in a hot and dense quark-gluon medium is obtained in the high-temperature limit for the case m≪gT and is solved explicitly for all |q| when μ=0. Four well-separated spectrum branches (quasi-particle and quasi-hole excitations) are found, and their behaviors for small and large |q| are investigated. All calculations are performed using the temperature Green function technique and fixing the Feynman gauge. The gauge dependence of the spectra found is briefly discussed. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 1, 3–8 (10 January 1998) Published in English in the original Russian journal. Edited by the Steve Torstveit.     

Dynamics of quark-gluon plasma from field correlators

It is argued that strong dynamics in the quark-gluon plasma and bound states of quarks and gluons is mostly due to nonperturbative effects described by field correlators. The emphasis in the paper is made on two explicit calculations of these effects from first principles—one analytic using gluelump Green’s functions and another using independent lattice data on correlators. The resulting hadron spectra are investigated in the range T _c ≤ T < 2T _c . The spectra of charmonia, bottomonia, light s mesons, glueballs, and quark-gluon states calculated numerically are in general agreement with lattice MEM data. The possible role of these bound states in the thermodynamics of quark—gluon plasma is discussed. The text was submitted by the authors in English.     

BRS anomaly in the fully quantized non-abelian gauge theory

The form of a possible anomalous term in Slavnov-Taylor identities of Yang-Mills theory is determined by making use of a cohomological exact sequence and the same method is applied to the theory with an anti-symmetric tensor gauge field. In both cases the unique anomalous term has the same form as the conventional non-abelian anomaly. The effect of the anomaly on the nilpotency of the BRS transformation is discussed also.     

Lorentz-non-invariant counter-terms in QCD in a general axial gauge

It is shown in the context of a pure Yang-Mills theory that the solution of the Slavnov-Taylor identities in a general axial gauge admits counter-terms which may or may not be Lorentz invariant. It follows from the background field method that these counter-terms must be gauge invariant. The Lorentz-non-invariant counter-terms appear already at the one-loop level and depend both on the gauge parameter α and the non-covariant vector n_ω.     

Slavnov-Taylor identities in Weinberg's renormalization scheme

Weinberg's renormalization scheme, although more cumbersome from the computational point of view, has a more immediate physical interpretation than 't Hooft's minimal renormalization scheme. It is expected to lead to smaller higher-order coefficients in a perturbative approach to QCD. However, it a priori violates the Slavnov-Taylor identities. A complete study of this problem is performed, both theoretically and for the practitioner's sake. The ambiguities in the choice of the tensorial basis of some of the QCD vertices, as well as the dependence in the gauge parameter are used for substantiating, eventually, the Slavnov-Taylor identities in this renormalization scheme.     

Gauge covariant linear response analysis of QCD plasma oscillations

We show, using linear response theory, how plasma oscillations and screening in quark-gluon plasma can be computed in perturbation theory in a gauge covariant manner. Using this method we calculate the damping constant of color electric plasma oscillations in a Colomb gauge and show that the result agrees with an earlier calculation in the A₀ = 0 gauge.     

Nordström's Theory Revisited

Maxwell–Nordström equations are rederived in the covariant form with respect to rotations in pseudo-orthogonal (4+1)-dimensional space, by the customary procedure of contraction of the excitation tensor and of the dual of the field tensor. For the invariance of these equations under time reversal T, the real fifth coordinate has to be odd with respect to the T-operation. Consequently, a new interpretation of the fifth coordinate is discussed, in which exp(it) is replaced by a function constructed from doubly-periodic Jacobian elliptic functions.