The proton spin sum rule chiral bag prediction, an update

Abstract

We reevaluate a quark model prediction using the new QCD evolution function calculated to the 3 loop order and conclude that this model compares favorably with the new experimental results.Comment: 10 pages, 2 figures available by request, give fax numbe

A possible resolution of the proton spin problem

“…Until now we have used the symbol Σ to denote the quark spin evaluated within a model. This has variously been identified in the literature with either Σ inv [35] or with the value measured at some relatively low scale, µ 2 < 1 GeV 2 . The difficulty arises because the flavor singlet spin operator has a divergence in QCD involving an operator of dimension 4, so that its matrix element is not renormalization group invariant.…”

Octet Spin Fractions and the Proton Spin Problem

“…In particular, we extract the quark spin content of the octet baryons from recent lattice QCD calculations. These are compared with the predictions of a relativistic quark model [32][33][34] which includes gluon exchange currents [15,35,36] and the meson cloud required by chiral symmetry [18,37]. The variation of the suppression of the fraction of the spin carried by quarks across the octet is striking and within the relatively large uncertainties in the lattice results (which should improve significantly in the near future) this is reproduced by the model.The lattice QCD calculations of the moments of the spindependent PDFs used here were based upon simulations involving 2 + 1 flavors of dynamical quarks, using the Symanzik improved gluon action and non-perturbatively O(a) improved Wilson fermions [38,39].…”

SU(3)-flavor breaking in octet baryon masses and axial couplings

“…They are also related to the quark spin content of the baryons [47]. In fact, assuming SU (3)-flavour symmetry, all octet baryon decays can be parametrized by just three quantities: the Cabbibo angle, θ C , and the F and D couplings [48,49].…”