Abstract:
The standard approximations of the Dyson--Schwinger equation lead to complex singularities of the fermion propagator. In three-dimensional QED one can show that this phenomenon might be related to confinement: a confining potential leads to mass-like singularities at complex momenta, and thus to the absence of a mass singularity on the real timelike axis. The correct treatment of the vacuum polarization is essential for the confining nature of QED3.

Abstract:
We investigate the influence of the full vacuum polarization and vertex function on the fermion propagator, using the coupled Dyson--Schwinger equations for the photon and fermion propagator. We show that, within a range of vertex functions, the general behavior of the fermion propagator does not depend on the exact details of the vertex, both in the massless and in the massive phase. Independent of the precise vertex function, there is a critical number of fermion flavors for dynamical mass generation in $(2+1)$-dimensional QED. A consistent treatment of the vacuum polarization is essential for these results.

Abstract:
We use the Bethe-Salpeter equation in rainbow-ladder truncation to calculate the ground state mesons from the chiral limit to bottomonium, with an effective interaction that was previously fitted to the chiral condensate and pion decay constant. Our results are in reasonable agreement with the data, as are the vector and pseudoscalar decay constants. The meson mass differences tend to become constant in the heavy-quark limit. We also present calculations for the pion and rho electromagnetic form factors, and for the single-quark form factors of the \eta_c and J/\psi.

Abstract:
In (2+1)-dimensional QED with a Chern-Simons term, we study dynamical breaking of chiral symmetry, using the Dyson--Schwinger equation for the fermions. There is a region in parameter space were dynamical chiral symmetry breaking occurs, just as in pure QED3 (without Chern--Simons term); outside this region, this chiral symmetry breaking solution does not exists. Our results, both numerically and analytically, show that the chiral phase transition is a discontinuous first-order transition.

Abstract:
We study meson and diquark bound states using the rainbow-ladder truncation of QCD's Dyson-Schwinger equations. The infrared strength of the rainbow-ladder kernel is described by two parameters. The ultraviolet behavior is fixed by the one-loop renormalization group behavior of QCD, which ensures the correct asymptotic behavior of the Bethe-Salpeter amplitudes and brings important qualitative benefits. The diquark with the lowest mass is the scalar, followed by the axialvector and pseudoscalar diquark. This ordering can be anticipated from the meson sector.

Abstract:
The ladder-rainbow truncation of the set of Dyson-Schwinger equations is used to study a variety of electroweak and strong processes involving light mesons. The parameters in the effective interaction are constrained by the chiral condensate and f_\pi; the current quark masses are fitted to m_\pi and m_K. The obtained electromagnetic form factors are in good agreement with the data. Also the weak K_{l3} decay and the radiative and strong decays of the vector mesons agree reasonably well with the data. Finally, we indicate how processes such as \pi-\pi scattering can be described within this framework as well.

Abstract:
The ladder-rainbow truncation of the set of Dyson-Schwinger equations is used to study the pion and kaon electromagnetic form factors and the $\gamma^\star \pi^0 \gamma$ transition form factor in impulse approximation. With model parameters previously fixed by the pseudoscalar meson masses and decay constants, the obtained form factors are in good agreement with the data.

Abstract:
The ladder-rainbow truncation of the set of Dyson-Schwinger equations is used to study light mesons. The parameters in the effective interaction are constrained by the chiral condensate and f_\pi; the current quark masses are fitted to m_\pi and m_K. The dressed quark propagators are in qualitative agreement with recent lattice-QCD results at low q^2 while having the correct perturbative behavior at large q^2. The resulting vector meson masses are within 5% of the experimental values. The obtained electromagnetic form factors and strong and electroweak coupling constants are also in good agreement with the data. At finite temperature, this truncation leads to a mean-field chiral phase transition. The spatial pion mass is almost constant below this transition, but rises with T close to and above T_c. The mass of its chiral partner, an idealized sigma meson, decreases with T until T_c, where it becomes degenerate with the pion.

Abstract:
The masses and decay constants of the light mesons are studied within a ladder-rainbow truncation of the set of Dyson-Schwinger equations using a model 2-point gluon function. The one phenomenological parameter and two current quark masses are fitted to reproduce $f_\pi$, $m_\pi$ and $m_K$. Our results for $f_K$, and for the vector mesons $\rho$, $\phi$, and $K^\star$ are in good agreement with the experimental values.

Abstract:
We calculate the critical exponents of the chiral phase transition at nonzero temperature using the thermal and chiral susceptibilities. We show that within a class of confining Dyson-Schwinger equation (DSE) models the transition is mean field, and that an accurate determination of the critical exponents requires extremely small values of the current-quark mass, several order of magnitude smaller than realistic up- and down-quark masses. In general, rainbow truncation models of QCD exhibit mean field exponents as a result of the gap equation's fermion substructure.