Abstract
We develop some new techniques extending the standard QCD sum-rules approach to hadron properties in alternating external fields. The string operator expansion in singularities near the light cone is used as a suitable alternative to the Wilson expansion in local operators. The response of soft vacuum quarks to external electromagnetic fields is characterized by photon wave functions which are studied in detail using the (approximate) conformal invariance of the theory. Sum rules are constructed, relating the amplitudes for the decay σ + → pγ to properties of the QCD vacuum in alternating magnetic fields. The resulting branching ratio and the azimuthal asymmetry turn out to be in agreement with the experimental data.
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