Challenges of Nuclear Shadowing in DIS

Nuclear shadowing in DIS at moderately small $x$ is suppressed by the nuclear formfactor and depends on the effective mass of a hadronic fluctuation of the virtual photon. We propose a solution to the problems (i) of how to combine a definite transverse size of the fluctuation with a definite effective mass, and (ii) of how to include the nuclear formfactor in the higher multiple scattering terms. Comparison of the numerical results with known approximations shows a substantial difference.