content_image/353477.jpg content_image/353478.jpg content_image/353479.jpg content_image/353480.jpg
The Mellin moments in the momentum fraction x are of major importance in the GPD approach. According to the polynomiality property of GPDs the x Mellin moments of gluon GPDs defined in (2), (3) are polynomials of ξ . The coefficients of these polynomials are related to the form factors of the local twist two gluon operators: 

<img src='content_image/353477.jpg'>

Here, as usual, D µ is the covariant derivative, S denotes symmetrization in all uncontracted Lorentz indices and subtraction of the appropriate traces. More technically, the polynomially property for unpolarized gluon GPDs means that for odd N : 

For the case of polarized gluon GPDs for even N 

## III. THE DUAL PARAMETRIZATION FOR GLUON GPDS 

<img src='content_image/353478.jpg'>

<img src='content_image/353479.jpg'>

Historically the first non-trivial phenomenological para-metrization of GPDs was the famous Radyushkin double distribution Ansatz (RDDA) suggested within the double dis- tribution representation of GPDs [9]. In particular, a version of RDDA was adopted for the case of gluon GPD H g in the nucleon (2) [10, 11]: 

<img src='content_image/353480.jpg'>

