Chiral quark model analysis of nucleon quark sea isospin asymmetry and spin polarization

Abstract

Abstract. We analyze recent measurements of the nucleon quark sea isospin asymmetry in terms of the chiral quark model. The new measurements indicate that the SU(3) model with modest symmetry breaking and no η ′ Goldstone boson gives a satisfactory description of data. We also discuss the matching parameter for the axial-vector current. Finally, we analyze the nucleon quark spin polarization measurements directly in the chiral quark model without using any SU(3) symmetry assumption on the hyperon axial-vector form factors. The new data indicate that the chiral quark model gives a remarkably good and consistent description of all low energy baryon measurements.

Flavor asymmetry of light quarks in the nucleon sea

“…An alternative approach [66,126,127,128,129,130,131] also employing virtual pions to produce thed,ū asymmetry is usually referred to as chiral models [101]. After the publication of the NMC result on the violation of the Gottfried sum rule, Eichten, Hinchliffe and Quigg (EHQ) [66], following an earlier suggestion of Bjorken [132], published an interesting approach to explain the NMC result.…”

CHIRAL QUARK MODEL (χQM) AND THE NUCLEON SPIN

“…where ∆Σ is the spin polarization contribution of the quarks, ∆L q is the orbital angular momentum of the quarks, ∆G is the gluon polarization and ∆L g is the orbital angular momentum of the gluons. Recently, some efforts have been made in the chiral quark model [17] and chiral quark soliton model [18] to understand the above sum rule. However, a detailed understanding of the partitioning of nucleon spin expressed through the sum rule does not seem to have been achieved, in particular, at present we do not have any clue about the likely magnitude of ∆L g either from the experiments or theoretical models.…”

“…To understand the partitioning of the nucleon spin in the χQM gcm , first we have to examine the various contributions to the nucleon spin which arise in the context of χQM. In the Cheng-Li version of χQM [22], at the leading order, the effective degrees of freedom are constituent quarks and the weakly interacting GBs which fluctuate into the "quark sea", however the gluon contribution through the gluon anomaly has also been discussed [17,32]. In the Adler-Bardeen scheme [37], the flavor singlet component of the spin of the proton is expressed as…”

Alternative method to obtain the quark polarization of the nucleon

“…[8]. Another approach has been taken by Ohlsson and Snellman [9], who employ the broken SU(3) symmetric chiral quark model [10] to analyze the nucleon quark spin polarization measurements directly, without using any SU(3) symmetry assumption. This was accomplished by fixing the symmetry-breaking parameters of the model with measurements by the NuSea Collaboration [11], [12] of the quark sea isospin asymmetries.…”

“…For instance, the value obtained for a 8 from a leading-order 1/N c expansion is much smaller that the value based on the SU(3) analysis. The use of a smaller value of a 8 causes a 0 to become larger [20], [9]. Symmetry breaking effects have been calculated under various assumptions leading to variations in the quantity 3F -D differing by a factor of two [21]- [25].…”