Parton Distribution within Virtual Photon and Diffractive Photoproduction in DIS

A simple relativistic model is suggested that elucidates qualitatively the quark-antiquark distribution within virtual photon. The diffractive hadroproduction in DIS initiated by highly virtual photon $\gamma ^{*}(Q^2)$ is discussed in more detail. The main result is that the contribution of large transverse scale $q\bar q$-fluctuations of the photon is just sufficient to produce the cross section of its hadron-like strong interaction (in particular, its diffraction into hadrons) of the same $Q^2$-dependence as the total cross section of $\gamma ^{*}p$-interaction. It is why observed in DIS fraction of photon diffractive hadroproduction in $\gamma^{*}p$\enspace interaction is quite large and does not vary with $Q^2$.