Pauli form factor of quark and nontrivial topological structure of the QCD

We calculate the electromagnetic Pauli form factor of quark induced by the nontrivial topological fluctuations of QCD vacuum called instantons. It is shown that such a contribution is significant. We discuss the possible implications of our result in the photon-hadron reactions and in the dynamics of quark-photon interactions in the dense/hot quark matter.

Figure 1

The diagrams with anomalous quark-gluon chromomagnetic vertex induced by instantons which contribute to EMFF of the quark. The vertex is denoted by a solid blob. $p$ and $p^{\prime }$ are the momenta of the external legs, $t$ is the momentum of the exchanged gluon.

Figure 2

The $F_2$ form factor as a function of $Q^2$ for the different dynamical quark mass $M_q$ in the comparison with the fit given by Eq. (17).

Figure 3

Behavior of ${\mu }_a^u$ versus quark mass: exact expression (black solid line), linear fit (blue dashed-dotted), expansion Eq. (24) (red dotted).