Threshold photon electroproduction off the proton allows one to measure new electromagnetic observables which generalize the usual polarizabilities. There are -a priori -ten "generalized polarizabilities", functions of the virtual photon mass. The purpose of this paper is to lay down the appropriate formalism to extract these quantities from the photon electroproduction cross sections.We also give a first estimate of the generalized polarizabilities in the non relativistic quark model.

We extend earlier investigations of charge symmetry violation in the valence quark distributions of the nucleon, and make similar estimates for the pion. The sensitivity of pion-induced Drell-Yan measurements to such effects is then examined. It is shown that combinations of π + and π − data on deuterium and hydrogen are sensitive to these violations, and that the pion and nucleon charge symmetry violating terms separate as a function of x π and x N respectively. We estimate the background terms which must be evaluated to extract charge symmetry violation.

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