Solving the nucleon spin puzzle based on the chiral quark soliton model

An incomparable feature of the chiral quark soliton model as compared with many other effective models like the MIT bag model is that it can give reasonable predictions not only for quark distributions but also for antiquark distributions. This will be exemplified by the argument on the positivity constraint for $\bar{u} (x) + \bar{d} (x)$ as well as the Soffer inequality for quark and antiquark distributions. We also explain how the model can resolve the so-called nucleon spin puzzle without assuming large gluon polarization at the low energy scale.