  In the spectator models of the nucleon with scalar and axial-vector diquarks,
we show that the effect of Pauli coupling in photon-quark vertex to the parton
distribution functions (PDFs) of nucleon and azimuthal asymmetry in the
unpolarized semi-inclusive deep inelastic scattering (SIDIS). This anomalous
coupling gives obvious contribution to unpolarized and polarized PDFs, and also
leads to a $\cos 2\phi_h$ azimuthal asymmetry proportional to the squared Pauli
form factor, due to the helicity flip of the struck quark. After determining
the model parameters by fitting PDFs to the global fits, this new distribution
for $\cos 2\phi_h$ asymmetry is given numerically. In the framework of
transverse momentum dependence (TMD), we find that it is positive and of a few
percent in the kinematical regime of HERMES and COMPASS collaborations, in the
same order of magnitude with Cahn effect.
