Nonperturbative quark-antiquark interactions in mesonic form factors
Edward Shuryak, Ismaïl Zahed
Abstract
The existing theory of hard exclusive QCD processes is based on two assumptions: (i) factorization into a hard block convoluted with the light front distribution amplitudes; (ii) use of perturbative gluon exchanges within the hard block. However, unlike deep inelastic scattering and jet physics, the characteristic momentum transfer $Q$ involved in the factorized block is not large enough for this theory to be phenomenologically successful. In this work, we revisit the latter assumption (ii), by explicitly calculating the instanton-induced contributions to the hard block, and show that they contribute substantially to the vector, scalar, and gravitational form factors of the pseudoscalar, scalar, and vector mesons, over a wide range of momentum transfer.