  Inclusive DIS with unpolarized beam exhibits a subtle dependence on the
transverse target spin, arising from the interference of one-photon and
two-photon exchange amplitudes in the cross section. We argue that this
observable probes mainly the quark helicity-flip amplitudes induced by the
non-perturbative vacuum structure of QCD (spontaneous chiral symmetry
breaking). This conjecture is based on (a) the absence of significant Sudakov
suppression of the helicity-flip process if soft gluon emission in the quark
subprocess is limited by the chiral symmetry-breaking scale mu_chiral^2 >>
Lambda_QCD^2; (b) the expectation that the quark helicity-conserving twist-3
contribution is small. The normal target spin asymmetry is estimated to be of
the order 10^{-4} in the kinematics of the planned Jefferson Lab Hall A
experiment.
