Related papers: Computing the perturbative gluon condensate
The running coupling constant can be estimated by computing gluon two- and three-point Green functions from the lattice. Computing in lattice implies working in a fixed gauge sector (Landau). An source of systematic uncertainty is then the…
I propose that the properties of QCD perturbation theory should be investigated when the boundary state (`perturbative vacuum') at $t= \pm\infty$ includes gluons. Any boundary state that has an overlap with the true QCD ground state…
Power corrections in QCD (both conventional and unconventional ones arising from the ultraviolet region) are discussed within the infrared finite coupling-dispersive approach. It is shown how power corrections in Minkowskian quantities can…
A simple parametrization of the QCD running coupling at low scales is introduced and used to illustrate various schemes for the estimation of non-perturbative power corrections. The `infrared matching' scheme proposed earlier gives…
Nonperturbative studies of the strong running coupling constant in the infrared region are discussed. Starting from the analyses of the Dyson -- Schwinger equations in the gauge sector of QCD, the conclusion is made on an incomplete fixing…
Although the methods of calculation of power corrections in QCD sum rules are well known, algebraic complexity rapidly grows with the increase of vacuum condensates' dimensions. Currently, state-of-the-art calculations include dimension 7…
The calculation of perturbative corrections to the spectral moments observable in hadronic $\tau$ decays is reconsidered. The exact order-$\alpha_s^3$ results and the resummation procedure of Le~Diberder and Pich are compared with a partial…
A physical characterization of Landau singularities is emphasized, which should trace the lower boundary N_f^* of the conformal window in QCD and supersymmetric QCD. A natural way to disentangle ``perturbative'' from ``non-perturbative''…
A new analysis of baryon sum rules is done with modern values of parameters and known perturbative corrections. The restriction for gluon and quark condensates and the new value of nucleon coupling constant are found.
The problem of precise evaluation of the perturbative QCD predictions at moderate energies is considered. Substantial renormalization scheme dependence of the perturbative predictions obtained with the conventional renormalization group…
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…
The gluon condensate, $\langle \frac{\alpha_s}{\pi} G^2 \rangle$, i.e. the leading order power correction in the operator product expansion of current correlators in QCD at short distances, is determined from $e^+ e^-$ annihilation data in…
There is considerable freedom in setting boundary conditions to perturbation theory at $t=\pm\infty$. The standard PQED and PQCD expansions are based on the (empty) perturbative vacuum. Since the true QCD ground state is expected to have a…
An analytic ghost-free model for the QCD running coupling $\alpha(Q^2)$ is proposed. It is constructed from a more general approach we developed particularly for investigating physical observables of the type $F(Q^2)$ in regions that are…
The perturbative part of the effective QCD Lagrangian was constructed by the renormalization group approach in the 4-loop approximation. It was extrapolated in the non-perturbative region under the assumption of the existence of gluon…
It is shown, that the possibility of a freezing of QCD running coupling constant at zero in the approach with "forced analyticity" can not be in accord with Schwinger-Dyson equation for gluon propagator. We propose to add to the analytic…
The following topics in perturbative QCD are reviewed: recent theoretical progress in higher-order calculations; soft-gluon resummation for hard-scattering processes at large $E_T$ and high $x$; low-$x$ behaviour of structure functions and…
The problem of improving the reliability of perturbative QCD predictions at moderate energies is considered. These predictions suffer from substantial renormalization scheme dependence, which is illustrated using as an example the QCD…
Sum rules for the nonperturbative piece of correlators (specifically, the vector current correlator) are discussed. The sum rule subtracting the perturbative part is of the superconvergent type. Thus it is dominated by the bound states and…
The problem of precise evaluation of perturbative QCD predictions at moderate energies is addressed. In order to improve stability of the predictions with respect to change of the renormalization scheme it is proposed to replace the…