98 10 43 3 v 2 2 5 N ov 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 sea is unpolarized 4 : ∆¯ u, ∆ ¯ d ≃ 0. All these features can be well and naturally understood in the chiral quark model (χQM) (for an incomplete list of references see [5,6]). The Chiral quark model: The effective Lagrangian in the model is 6