The ratio of sigma_L/sigma_T in DIS at low x

Assuming helicity independence for q-qbar scattering in the color-dipole picture, or, equivalently proportionality of sea quark and gluon distributions, we find R(W^2,Q^2) = 0.5 (approximately) at large Q^2, where R(W^2,Q^2) denotes the ratio of the longitudinal and transverse photoabsorption cross sections. The forthcoming direct measurements of R(W^2,Q^2) allow one to test the underlying hypotheses.