THE ROLE OF THE PION CLOUD IN THE INTERPRETATION OF THE VALENCE LIGHT-CONE WAVE-FUNCTION OF THE NUCLEON

The pion cloud renormalises the light-cone wave-function of the nucleo n which is measured in hard, exclusive photon-nucleon reactions. We di scuss the leading twist contributions to high-energy exclusive reactio ns taking into account both the pion cloud and perturbative QCD physic s. The nucleon's electromagnetic form-factor at high Q(2) is proportio nal to the bare nucleon probability Z and the cross-sections for hard (real at large angle or deeply virtual) Compton scattering are proport ional to Z(2). Our present knowledge of the pion-nucleon system is con sistent with Z = 0.7 +/- 0.2. If we apply just perturbative QCD to ext ract a light-cone wavefunction directly from these hard exclusive cros s-sections, then the light-cone wavefunction that we extract measures the three valence quarks partially screened by the pion cloud of the n ucleon. We discuss how this pion cloud renormalisation effect might be understood at the quark level in terms of the (in-)stability of the p erturbative Dirac vacuum in low energy QCD.