Related papers: About an Alternative Vacuum State for Perturbative…
A particular initial state for the construction of the perturbative expansion of QCD is investigated. It is formed as a coherent superposition of zero momentum gluon pairs and shows Lorentz as well as global SU(3) symmetries. It follows…
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…
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…
QCD perturbation theory using quark and gluon propagators that have an extra term at zero four-momentum is equivalent to standard PQCD in the presence of massless quark and gluon pairs in the perturbative vacuum. We verify at low orders in…
The quark <\bar\psi \psi> and gluon <F_{\mu\nu}F^{\mu\nu}> vacuum expectation values are non-vanishing at low orders in \alpha_s when the perturbative ground state includes quark and gluon pairs. This offers possibilities of studying the…
Motivated by the gluon condensate in QCD we study the perturbative expansion of a gauge theory in the presence of gauge bosons of vanishing momentum, in the specific case of an abelian theory. The background is characterised by a…
These lecture notes focus on the bound state sector of QCD. Motivated by data which suggests that the strong coupling \alpha_s(Q) freezes at low Q, and by similarities between the spectra of hadrons and atoms, I discuss if and how QCD bound…
We consider a local, renormalizable, BRST-invariant action for QCD in Coulomb gauge that contains auxiliary bose and fermi ghost fields. It possess a non-perturbative vacuum that spontaneously breaks BRST-invariance. The vacuum condition…
The normalization of the gluon condensate and of renormalon-related power corrections in QCD is computed under the assumption that their ``perturbative'' part dominates over any eventual extra contribution from the non-trivial vacuum. The…
The renormalization scheme for the Wick expansion of a modified version of the perturbative QCD introduced in previous works is discussed. Massless QCD is considered, by implementing the usual multiplicative scaling of the gluon and quark…
A perturbative expansion for QED and QCD bound states is formulated in $A^0=0$ gauge. The constituents of each Fock state are bound by their instantaneous interaction. In QCD an O($\alpha_s^0$) confining potential arises from a homogeneous…
This talk reports on work aimed at improving our understanding of charged states in gauge theories.Emphasis is placed on different ways of implementingthe gauge invariance of physical states. QED perturbative calculations are used to stress…
None of the asymptotic states commonly used in perturbative QCD are gauge invariant. A similar statement could be made about QED, but in QED one can construct gauge invariant "dressed" states (with Dirac electrons) that are unitarily…
In this paper we investigate the Yokoyama gaugeon formalism for perturbative quantum gravity in a general curved spacetime. Within the gaugeon formalism, we extend the configuration space by introducing vector gaugeon fields describing a…
The problem of the gluonic quasiparticle excitations in QCD is considered under the aspect of the condensation of gluon pairs in the ''squeezed'' vacuum. The present approach is a field theoretical generalization of the Bogoliubov model…
We propose an alternative perturbative expansion for QCD. All scheme and scale dependence is reduced to one free parameter. Fixing this parameter with a fastest apparent convergence criterion gives sensible results in the whole energy…
Phenomenological evidence and analytic approximations to the QCD ground state suggest a complex gluon condensate structure. Exclusion of elementary fermion excitations by the generation of infinite mass corrections is a consequence. In…
QCD perturbation theory ignores the compact nature of $SU(3)$ gauge group that gives rise to the periodic $\theta$-vacuum of the theory. We propose to modify the gluon propagator to reconcile perturbation theory with the anomalous Ward…
The nonperturbative vacuum structure which emerges from the zero modes enhancement (ZME) model of the true QCD vacuum, appears to be well suited to describe quark confinement, dynamical chiral symmetry breaking (DCSB), current-effective…
The structure of the beta function of massless QCD is considered in analytic perturbation theory (APT). The two-loop analytic effective coupling is written in terms of the Lambert W function. The method of APT is applied to the gluon…