Nonpartonic components in the nucleon structure functions at small Q2 in a broad range of x

We construct a simple two-phase model of the nucleon structure functions valid for both small and large Q2 and in the broad range of Bjorken x. The model incorporates hadron dominance at small x and Q2 and parton model at large Q2. The VDM contribution is modified for small fluctuation times of the hadronic state of the photon. With two free parameters we describe SLAC, CERN NMC, Fermilab E665 and CERN BCDMS data for both proton and deuteron structure functions. Our model explains some phenomenological higher-twist effects extracted from earlier analyses. A good description of the NMC F2p(x)-F2n(x) data is obtained in contrast to other models in the literature. We predict faster vanishing of the partonic component at low Q2 than previously expected and strong Q2 dependence of the Gottfried sum rule below Q2 ∼ 4 GeV2. (orig.)