Nonperturbative quark-antiquark interactions in mesonic form factors

TL;DR

This paper investigates nonperturbative instanton effects in mesonic form factors, challenging the standard perturbative approach and showing significant contributions across various meson types and momentum transfers.

Contribution

It explicitly calculates instanton-induced contributions to the hard scattering kernel, revealing their substantial impact on mesonic form factors.

Findings

Instanton effects significantly influence mesonic form factors.

Nonperturbative contributions are important over a wide momentum range.

Challenging the reliance on perturbative gluon exchanges in QCD processes.

Abstract

The existing theory of hard exclusive QCD processes is based on two assumptions: (i) $factorization$ into a $hard\,block$ times light front distribution amplitudes (DA's); (ii) use of perturbative gluon exchanges within the hard block. However, unlike DIS 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.