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QCD theory allows the existence of states which cannot be built by the naive quark model; both theoretical arguments and experimental data confirm the hypothesis that gluons may have freedom degrees at the constituent level, and should be…
In $SU(N)$ gauge theories without dynamical quarks, we discuss how configurations with fractional topological charge, $\sim 1/N$, can arise in the vacuum and dominate in the confining phase. They are not solutions of the classical equations…
Using superfield Dyson-Schwinger equations, we compute the infrared dynamics of the semi-amputated full vertex, corresponding to the effective running gauge coupling, in N-flavour {\mathcal N}=1 supersymmetric QED(3). It is shown that the…
We have formulated new quantum model of the QCD vacuum using the effective potential approach for composite operators. It is based on the existence and importance of such kind of the nonperturbative, topologically nontrivial excitations of…
A serious difficulty in conventional lattice field theory calculations is the coupling between the chiral and continuum limits. With both staggered and Wilson fermions, the chiral limit cannot be realized without first taking the limit of…
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…
I examine a set of Feynman rules, and the resulting effective action, that were proposed in order to incorporate the constraint of Gauss's law in the perturbation expansion of gauge field theories. A set of solutions for the Lagrangian and…
The gap equation is a cornerstone in understanding dynamical chiral symmetry breaking and may also provide clues to confinement. A symmetry-preserving truncation of its kernel enables proofs of important results and the development of an…
Using the Dyson-Schwinger approach we investigate Landau gauge QCD with a relatively large number of chiral quark flavours. A self-consistent treatment on the propagator level enables us to study unquenching effects via the quark loop…
The fermion sign problem poses a formidable challenge to the use of Monte Carlo methods for lattice gauge theories with dynamical fermionic matter fields. A meron cluster algorithm recently formulated for gauge fields represented as…
Phenomenological consequences of the infrared singular, instantaneous part of the gluon propagator in Coulomb gauge are investigated. The corresponding quark Dyson-Schwinger equation is solved, neglecting retardation and transverse gluons…
The Dirac structure of confinement is shown to be of timelike-vector nature in the heavy quark limit of QCD. This stands in contradiction with the phenomenological success of the Dirac scalar confining potential. A resolution is achieved…
Quantum Link Models with dynamical matter coupled to spin-$\frac{1}{2} \ \rm U(1)$ gauge fields in $d=2+1 $ and $3+1$ can potentially give rise to the Coulomb phase expected in quantum electrodynamics (QED) and other confining phases. Using…
We exhibit the method for obtaining non perturbative quark and gluonic vacuum condensates from a model truncation of QCD. The truncation allows for a phenomenological description of the quark-quark interaction in a framework which maintains…
The QCD-like gauge theory with adjoint fermions is considered in the field correlator formalism and the total spectrum of mesons and glueballs is obtained in agreement with available lattice data. A new state of a white fermion appears, as…
Transition form factors $F_{P\gamma^*\gamma^{(*)}}$ of pseudoscalar mesons are studied within the framework of the domain model of confinement, chiral symmetry breaking and hadronization. In this model, the QCD vacuum is described by the…
We provide a study of quantum chromodynamics with the technique of Dyson-Schwinger equations in differential form. In this way, we are able to approach the non-perturbative limit and recover, with some approximations, the 't Hooft limit of…
We investigate a proposal to address several outstanding shortcomings of the perturbative Standard Model (SM) of particle physics. The appeal of this proposal is that these features are a manifestation of the non-perturbative sector of the…
We investigate the glueball spectrum for $N_f=4$ fermions corresponding to low pion masses of $m_\pi \sim 250$MeV. We do so by making use of configurations produced with maximally twisted fermions within the framework of the Extended…
The large-distance dynamics in quarkonium systems is investigated, in the large N limit, through the saturation of Wilson loop averages by minimal surfaces. Using a representation for the quark propagator in the presence of the external…