The π→eνγdecay: a measurement of the four-quark component of the pion wave function

The axial part of the π→eνγ decay is analyzed in two different ways with the help of the wave function of the pion beyond the light cone and by using an asymptotic expansion of the initial matrix element over the local operators in the framework of the standard QCD sum rules technique. Within the latter approach the axial form factor turns out to be determined by the four-quark component of the whole pion wave function. The results of the calculation for the vector form are also given and the relation between vector and axial form factors is discussed. (orig.)