Low-x behavior of spin structure functions: unitarity and   nonperturbative hadron structure
  We consider low-x behavior of the spin structure functions g_1(x) and h_1(x) in the unitarized chiral quark model that combines the ideas on constituent quark structure of hadrons with a geometrical scattering picture and unitarity. A nondiffractive singular low-x dependence of g^p_1(x) and g_1^n(x) is obtained and a diffractive type smooth behavior of h_1(x) is predicted at small x. 
Sergey Troshin and Nikolai Tyurin