Unitarity and nonperturbative effects in the spin structure functions at small $x$
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 $x$.