A phenomenological Dyson-Schwinger equation approach to QCD, formalised in terms of a QCD based model field theory, is used to calculate the electromagnetic charge radius of the pion. The contributions from the quark core and pion loop, as defined in this approach, are identified and compared. It is shown explicitly that the divergence of the charge radius in the chiral limit is due to the pion...

We study the non-forward matrix elements of twist–2 QCD light–ray operators and their representations in terms of skewed and double distributions, considering the pion as well as the nucleon. We point out the importance of explicitly including all twist–2 structures in the double distribution representation, which naturally leads to a " two–component " structure of the skewed distribution, with...

We derive a set of new consistency conditions for the pion-pion scattering amplitude. These conditions hold for any s, t, u in the cube, 0 5 s, t, u 2 P2, with the four external mass variables off -mass -shell and restricted such that 4:. = 0, qt = s, 432 = t, and c$ = u. Using these consistency conditions, we determine the coefficients of the power series expansion of the pion-pion amplitude u...

The partial restoration of chiral symmetry in nuclear medium is investigated in a model independent way by exploiting operator relations in QCD. An exact sum rule is derived for the quark condensate valid for all density. This sum rule is simplified at low density to a new relation 〈q̄q〉∗/〈q̄q〉 = (F t π/Fπ)Z ∗1/2 π with the in-medium quark condensate 〈q̄q〉 ∗, in-medium pion decay constant F t π an...

Role of ∆ exchange for p¯ p annihilation into two-pion and three-pion channels Abstract p¯ p annihilation into two pions and three pions is studied in a baryon-exchange model. Annihilation diagrams involving nucleon as well as ∆-resonance exchanges are included consistently in the two-and three-pion channels. Effects from the initial-state interaction are fully taken into account. A comparison ...