Unpolarized and polarized quark distributions in the large-Nclimit

Abstract

The isosinglet unpolarized and isovector polarized twist-2 quark distributions of the nucleon at low normalization point are calculated in the large-N c limit. The nucleon is described as a soliton of the effective chiral theory. We derive the expressions for the distribution functions in the large-N c limit starting from their definition as numbers of partons carrying momentum fraction x in the infinite momentum frame. We develop a numerical method for computation of the quark and antiquark distributions as sums over the quark single-particle levels in the pion field of the soliton. The contributions of the discrete bound-state level as well as the Dirac continuum are taken into account. The quark-and antiquark distributions obtained explicitly satisfy all general requirements. Results are in reasonable agreement with parametrizations of the data at low normalization point.

Predictions for azimuthal asymmetries in pion and kaon production in SIDIS off a longitudinally polarized deuterium target at HERMES

“…Due to the field-theoretical nature of the χQSM, the quark and antiquark distribution functions computed in the model satisfy all general QCD requirements (positivity, sum rules, inequalities) [17]. The model results for the known distribution functions -f q 1 (x), fq 1 (x) and g q 1 (x) -agree within (10 -30)% with phenomenological parameterizations [18]. This encourages confidence in the model predictions for h a 1 (x).…”

“…In a sense the assumption eq. (18) formulates the naive expectation that the 'way off chiral limit to real world' proceeds analogously for spin-dependent quantities, H ⊥ 1 , and for quantities containing no spin information, D 1 .…”

Instantons at work

“…On the contrary, being a relativistic field-theoretic model CQSM predicts parton distributions that satisfy all general requirements known in full QCD, like positivity and sum rules constraints. Numerous parton distributions have been computed in the CQSM, mainly by the Bochum group [119,120,121], see also [122,123,124] and references therein. There have been a number of mysteries from naive quark models' point of view: the large number of antiquarks already at a low virtuality, the 'spin crisis' [125], the large flavour asymmetry of antiquarks, etc.…”

“…in the nucleon at low virtuality [119]. Parton distributions are a snapshot of the nucleon in the infinite momentum frame.…”

Hadron structure functions in a chiral quark model

“…This has been motivated by the observation that the regularized vacuum contributions to static nucleon properties are small once the self-consistent soliton solution is determined. Later approaches including vacuum contributions imposed a single subtraction regularization scheme at the level of (constituent) quark distributions [8,9]. The regularization attributed to a given structure function was conjectured to equal that of the corresponding sum rule associated with static nucleon properties.…”