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A new rigorous light-cone path integral approach to the Landau-Pomeranchuk-Migdal effect in QED and QCD is discussed. The rate of photon (gluon) radiation by an electron (quark) in a medium is expressed through the Green's function of a…
We summarise results for the propagators of Landau gauge QCD from the Green's functions approach and lattice calculations. The nonperturbative solutions for the ghost, gluon and quark propagators from a coupled set of Dyson-Schwinger…
Models incorporating moderately heavy dark matter (DM) typically need charged (scalar) fields to establish admissible relic densities. Since the DM freezes out at an early epoch, thermal corrections to the cross sections can be important.…
We study an extended Gross-Neveu model with $N_f$ quark flavors and with an additional SU(2) (global color) degree of freedom of the quarks. The four fermion interaction in the color channel is mediated by a random color matrix with fixed…
We consider the class of gauges that interpolates between Landau- and Coulomb-gauge QCD, and show the non-renormalisation of the two independent ghost-gluon vertices. This implies the existence of two RG-invariant running couplings, one of…
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 multiple scattering formalism is used to extract irreducible N-body parts of Green's functions and Casimir energies describing the interaction of N objects that are not necessarily mutually disjoint. The irreducible N-body scattering…
We summarize recent results obtained in the Dyson-Schwinger formalism to study the chiral and deconfinement phase transitions of quenched and unquenched QCD at finite temperature and chemical potential. In the quenched case we compare SU(2)…
Green's functions in Physics have proven to be a valuable tool for understanding fundamental concepts in different branches, such as electrodynamics, solid-state and many -body problems. In quantum mechanics advanced courses, Green's…
Gauge theories are characterised by long range interactions. Neglecting these interactions at large times, and identifying the Lagrangian matter fields with the asymptotic physical fields, leads to the infra-red problem. In this paper we…
I give a brief account of Gribov's scenario of supercritical charges in QCD. Gribov's equation for the Green function of light quarks and its derivation from the corresponding Dyson-Schwinger equation are described. The resulting Green…
Recently the quark-gluon vertex has been investigated in Landau gauge using a combined Dyson-Schwinger and nPI effective action approach. We present here a numerical analysis of a simpler system where the quarks have been replaced by…
Solutions for the three-gluon and quark-gluon vertices from Dyson-Schwinger equations and the three-particle irreducible formalism are discussed. Dynamical quarks (``unquenching'') change the three-gluon vertex via the quark-triangle…
In the thesis, first, the cancellation of infrared divergences in QED is reviewed. Next, two examples in QCD, the quark-quark scattering and the quark-gluon scattering are examined at one loop, from which the importance of Ward-Takahashi…
We calculate the scalar, axial, and pseudoscalar charges of the quark in the Schwinger-Dyson formalism of Landau gauge QCD. It is found that the dressed quark scalar density of the valence quark is significantly enhanced against the bare…
The general method for treating non-Gaussian wave functionals in the Hamiltonian formulation of a quantum field theory, which was previously proposed and developed for Yang--Mills theory in Coulomb gauge, is generalized to full QCD. For…
A modified version of PQCD considered in previous works is investigated here in the case of retaining only the quark condensate. The Green functions generating functional is expressed in a form in which Dirac's delta functions are now…
Theoretical understanding of experimental results from relativistic heavy-ion collisions requires a microscopic approach to the behavior of QCD n-point functions at finite temperatures, as given by the hierarchy of Dyson-Schwinger…
The center phase transition of QCD and of fundamentally charged scalar QCD at non-vanishing temperature is investigated within a Dyson-Schwinger approach. The temperature dependence of the scalar/quark propagator is studied with generalized…
The infra-red behaviour of gauge theories coupled to matter remains an open problem in quantum field theory. For a given gauge group, such theories are expected to flow to an interacting conformal fixed point over a range of fermion or…