Generalized parton distributions for weakly bound systems from light-front quantum mechanics

We present generalized parton distributions for weakly bound systems on the light cone in order to build intuition about the light-front formalism. Physics at the crossover is reviewed in terms of the light-cone Fock space representation. Furthermore, we link light-cone Fock components to the equal (light-cone) time projection of the covariant Bethe-Salpeter amplitude. Continuity of the distributions arises naturally in this weak binding model.Comment: 6 pages, 2 figures. Talk given at conference, "Exclusive Processes at High Momentum Transfer," held at Jefferson Laboratory, May 15-18, 200

Chiral Lattice Fermions, Minimal Doubling, and the Axial Anomaly

Exact chiral symmetry at finite lattice spacing would preclude the axial anomaly. In order to describe a continuum quantum field theory of Dirac fermions, lattice actions with purported exact chiral symmetry must break the flavor-singlet axial symmetry. We demonstrate that this is indeed the case by using a minimally doubled fermion action. For simplicity we consider the Abelian axial anomaly in two dimensions. At finite lattice spacing and with gauge interactions, the axial anomaly arises from non-conservation of the flavor-singlet current. Similar non-conservation also leads to the axial anomaly in the case of the naive lattice action. For minimally doubled actions, however, fine tuning of the action and axial current is necessary to arrive at the anomaly. Conservation of the flavor non-singlet vector current additionally requires the current to be fine tuned. Finally we determine that the chiral projection of a minimally doubled fermion action can be used to arrive at a lattice theory with an undoubled Dirac fermion possessing the correct anomaly in the continuum limit.Comment: 15 pages, 1 figure, symmetries corrected, Symanzik analysis for currents added, marginal operators expose

Hadronic Parity Violation at Next-to-Leading Order

The flavor-conserving non-leptonic weak interaction can be studied experimentally through the observation of parity violation in nuclear and few-body systems. At hadronic scales, matrix elements of parity-violating four-quark operators ultimately give rise to the parity violating couplings between hadrons, and such matrix elements can be calculated non-perturbatively using lattice QCD. In this work, we investigate the running of isovector parity-violating operators from the weak scale down to hadronic scales using the renormalization group. We work at next-to-leading order in the QCD coupling, and include both neutral-current and charged-current interactions. At this order, results are renormalization scheme dependent, and we utilize 't Hooft-Veltman dimensional regularization. The evolution of Wilson coefficients at leading and next-to-leading order is compared. Next-to-leading order effects are shown to be non-negligible at hadronic scales.Comment: 16 pages, 2 figures, v2: statements pertaining to isovector parity violation corrected, refs added, results unchange