An exact representation of the causal QED fermion Greens function, in an arbritrary external electromagnetic field, derived by Fried, Gabellini and McKellar, and which naturally allows for non-perturbative approximations, is here used to calculate no
n-perturbative approximations to the Greens function in the simple case of a constant external field. Schwingers famous exact result is obtained as the limit as the order of the approximation approaches infinity.
We note that off the quark mass shell the operators $(p_i+p_f)_mugamma_5$ and $isigma_{mu u}(p_i -p_f)^ ugamma_5$, both of which reduce to $-vec{sigma}cdotvec{E}$ in the non-relativistic limit, are no longer identical. In this paper we explore the ef
fects of this difference in the contribution of these quark electric moments to hadronic electric moments.
The $O(v^2)$ relativistic correction for inelastic $J/psi$ photoproduction, in which heavy quark pairs are in the dominant Fock state of the quarkonium, is studied in the framework of NRQCD factorization. An assessment of its significance, particular
ly in comparison to the color octet contributions, is made. It is found that the impact on the energy distribution is negative in certain regions of phase space. The predictions are compared with photoproduction data from DESY-HERA.
We study $J/Psi$ production at photon-photon colliders, which can be realised with Compton scaterring of laser photons at $e^+e^-$ colliders. We find that the production rate through the color-octet channel is comparable to that through the color-sin
glet channel. Experimentally the two mechanisms can be studied separately because the processes have different signals.
We use improved lattice actions for glue, light quarks and heavy quarks for which we use lattice NRQCD to compute hadron masses. Our results are in good agreement with experiment, except for charmed hadrons. It seems that charmed quar ks are not well approximated as heavy quarks nor as light quarks.
Phenomenological Lagrangians that exhibit (broken) chiral symmetry as well as isospin violation suggest short-range charge symmetry breaking (CSB) nucleon-nucleon potentials with a $mbox{boldmath $sigma$}_1 !cdot!mbox{boldmath $sigma$}_2$ structure.
This structure could be realized by the mixing of axial-vector ($1^+$) mesons in a single-meson exchange picture. The Coleman-Glashow scheme for $Delta I_{z}=1$ charge symmetry breaking applied to meson and baryon $SU(2)$ mass splittings suggests a universal scale. This scale can be extended to $Delta I=1$ nonstrange CSB transitions $langle a_1^circ|H_{em}|f_1rangle$ of size $-0.005$ GeV$^2$. The resulting nucleon-nucleon axial-vector meson exchange CSB potential then predicts $Delta I=1$ effects which are small.
