ar X iv : h ep - p h / 98 04 39 7 v 1 2 4 A pr 1 99 8 Quark and Gluon Orbital Angular Momentum and Spin in Hard Processes ∗

ar X iv : h ep - p h / 98 04 39 7 v 2 2 5 A pr 1 99 8 Quark and Gluon Orbital Angular Momentum and Spin in Hard Processes ∗

We suggest a method of constructing gauge invariant quark and gluon distributions that describe an abstract QCD observable and apply this method to analyze angular momentum of a hadron. In addition to the known quark and gluon polarized structure functions, we obtain gauge invariant distributions for quark and gluon orbital angular momenta, and consider some basic properties of these distributi...

ar X iv : h ep - p h / 98 10 43 3 v 1 2 1 O ct 1 99 8 SPIN AND ORBITAL ANGULAR MOMENTUM IN THE CHIRAL QUARK MODEL

Quark spin and orbital angular momentum in the nucleon are calculated in symmetry-breaking chiral quark model. The results are compared with data and other models. Synopsis: Recent measurements show (1) strong flavor asymmetry of the antiquark sea 1 : ¯ d > ¯ u, (2) nonzero strange quark content 2 : < ¯ ss > = 0, (3) sum of quark spins is small 3 : < s z > q+¯ q = 0.1 − 0.2, and (4) antiquark s...

X iv : h ep - t h / 98 10 04 5 v 1 7 O ct 1 99 8 TPI - MINN - 98 / 04 Quasi - Exactly Solvable Models with Spin - Orbital Interaction

First examples of quasi-exactly solvable models describing spin-orbital interaction are constructed. In contrast with other examples of matrix quasi-exactly solvable models discussed in the literature up to now, our models admit infinite (but still incomplete) sets of exact (algebraic) solutions. The hamiltonians of these models are hermitian operators of the form H = −∆ +V1(r)+ (s · l)V2(r)+ (...

ar X iv : h ep - p h / 98 04 40 7 v 1 2 6 A pr 1 99 8 B c → l ν̄γ DECAY IN LIGHT CONE QCD

ar X iv : h ep - p h / 96 12 25 2 v 2 2 1 Ju l 1 99 7 Large N c Limit of Spin - Flavor Breaking in Excited Baryon Levels

Spin-flavor symmetry breaking in the levels of excited Baryons are studied to leading order in the 1/N c expansion. This breaking occurs at zeroth order. For non-strange Baryons with a single quark excited, it is shown that to first order of perturbation theory the breaking is given by one 1-body operator (spin-orbit), and three 2-body operators, all involving the orbital angular momentum of th...