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: 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 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]: III. THE DUAL PARAMETRIZATION FOR GLUON GPDS O µµ$_{1}$...µ$_{n}$ν g = S F $^{µα}$i ← → D $^{µ$_{1}$}$...i ← → D $^{µ$_{n}$}$F ν α ; ˜ O µµ$_{1}$...µ$_{n}$ν g = S ( − i ) F $^{µα}$i ← → D $^{µ$_{1}$}$...i ← → D µ$_{n}$ ˜ F ν α . (8) ∫ 1 0 dxx N − $^{1}$H $^{g}$( x, ξ, t ) = N + mod ( N, 2) ∑ k =0 even ξ $^{k}$h g $_{N,k}$( t ) ; ∫ 1 0 dxx N − $^{1}$E $^{g}$( x, ξ, t ) = N + mod ( N, 2) ∑ k =0 even ξ $^{k}$e g $_{N,k}$( t ) with e g N,N $_{+1}$( t ) = − h g N,N $_{+1}$( t ) . (9) ∫ 1 0 dxx N − 1 ˜ H $^{g}$( x, ξ, t ) = N ∑ k =0 even ξ k ˜ h g $_{N,k}$( t ) ; ∫ 1 0 dxx N − 1 ˜ E $^{g}$( x, ξ, t ) = N ∑ k =0 even ξ $^{k}$˜ e g $_{N,k}$( t ) . (10) H $^{g}$( x, ξ, t = 0) = H g $_{DD}$( x, ξ ) + 2 θ ( ξ − | x | ) ξD g ( x ξ ) , (11) 5