Related papers: 1/Q^2 terms and Landau singularity
We revisit the extraction of $\alpha_s(M_\tau^2)$ from the QCDperturbative corrections to the hadronic $\tau$ branching ratio, using an improved fixed-order perturbation theory based on the explicit summation of all renormalization-group…
We summarize the most important arguments why a perturbative description of finite-temperature QCD is unlikely to be possible and review various well-established approaches to deal with this problem. Then, using a recently proposed method,…
The `renormalon' or `dispersive' method for estimating non-perturbative corrections to QCD observables is reviewed. The corrections are power-suppressed, i.e. of the form $A/Q^p$ where $Q$ is the hard process momentum scale. The renormalon…
In this contribution to the proceedings, we analyze the transition from perturbative and non- perturbative QCD embedded in the coupling constant. In the study of quark-hadron duality, we suggest that the realization of the latter is related…
In this work the determination of low-energy bound states in Quantum Chromodynamics is recast so that it is linked to a weak-coupling problem. This allows one to approach the solution with the same techniques which solve Quantum…
Perturbative expansion in the nonperturbative confining QCD background is formulated. The properly renormalized $\alpha_S(R)$ is shown to be finite at large distances, with the string tension playing the role of an infrared regulator. The…
The Landau problem is discussed in two similar but still different non-commutative frameworks. The ``standard'' one, where the coupling to the gauge field is achieved using Poisson brackets, yields all Landau levels. The ``exotic''…
We try to review the main current ideas and points of view on the running coupling constant in QCD. We begin by recalling briefly the classic analysis based on the Renormalization Group with some emphasis on the exact solutions of the RG…
We apply the optimization procedure based on the Principle of Minimal Sensitivity to the third-order calculation of $R_{\tau}$. Since the effective couplant remains finite, freezing to a value $\alpha_s/\pi = 0.26$ at low energies, we can…
In quantum theory, physical amplitudes are usually presented in the form of Feynman perturbation series in powers of coupling constant $\al .$ However, it is known that these amplitudes are not regular functions at $\alpha=0 .$ For QCD, we…
String tension is introduced in perturbative QCD without hindering ultra violet renormalizability . The running gauge coupling constant remains unaltered and the string tension in the high energy limit vanishes asymptotically. Using 1/N…
The QCD running coupling $\alpha_s(Q^2)$ sets the strength of the interactions of quarks and gluons as a function of the momentum transfer $Q$. The $Q^2$ dependence of the coupling is required to describe hadronic interactions at both large…
A technique called analytic perturbation theory, which respects the required analytic properties, consistent with causality, is applied to the definition of the running coupling in the timelike region, to the description of inclusive…
We incorporate the concept of dimensional reduction at high energies within the perturbative formulation of quantum field theory. In this new framework, space and momentum integrations are modified by a weighting function incorporating an…
In this paper, we argue that the Landau singularity of the coupling constant in QED reflects the instability of vacuum state, in other words the perturbative ground state in QED.We do not have a rigorous mathematical proof. We rather…
For high energy processes ($M\gg \Lambda_{QCD}$) there are infrared safe hadronic shape variables that have a calculable perturbative expansion in $\alpha_s(M^2)$. However, nonperturbative power suppressed corrections to these variables are…
Demanding the analyticity of hadronic observables (calculated in terms of power series of the running coupling) as a {\it whole}, we show that they are free of the Landau singularity. Employing resummation and dispersion-relation…
Classical Landau theory considers structural phase transitions and crystallization as a condensation of several critical density waves whose wave vectors are symmetrically equivalent. Analyzing the simplest nonequilibrium Landau potentials…
A structural explanation of the coupling constants in the standard model, i.e the fine structure constant and the Weinberg angle, and of the gauge fixing contributions is given in terms of symmetries and representation theory. The coupling…
We consider perturbative expansions in theories with an infrared cutoff $\lambda$. The infrared sensitive pieces are defined as terms nonanalytic in the infinitesimal $\lambda^2$ and powers of this cutoff characterize the strength of these…