Phenomenology of forward hadrons in deep inelastic scattering: Fracture functions and its $Q^2$ evolution

We analyze recent data on the production of forward neutrons in deep inelastic scattering at DESY HERA in the framework of a perturbative QCD description for semi-inclusive processes, which includes fracture functions. Using a model estimate for the nonperturbative piece of the fragmentation process, in fairly good agreement with the available data, we analyze the $Q^2$ dependence of the resulting fracture functions, which is driven by nonhomogeneous evolution equations. We also propose a measurement of the pion production cross section in the target fragmentation region as a new test of perturbative QCD, which in this case predicts also a different $Q^2$ evolution with respect to the one given by the usual Altarelli-Parisi equations.