Isospin dependence of power corrections in deep inelastic scattering

We present results of a perturbative QCD analysis of deep inelastic measurements of both the deuteron and proton structure functions. We evaluate the theoretical uncertainty associated with nuclear effects in the deuteron, and we extract simultaneously the isospin dependence of (i) the higher twists terms, (ii) the ratio of the longitudinal to transverse cross sections, $R={\ensuremath{\sigma}}_{L}/{\ensuremath{\sigma}}_{T},$ and (iii) the ratio of the neutron to proton structure functions, ${F}_{2}^{n}{/F}_{2}^{p}.$ The extraction of the latter, in particular, has been at the center of an intense debate. Its accurate determination is crucial both theoretically and for the interpretation of the more precise neutrino experiments including the newly planned high intensity 50 GeV proton synchrotron.