This results in the following expression for the D form factor: The value of C N − $^{Q$_{0}$}$(0) is necessarily negative in order to reduce the skewness effect for small ξ (see (85)). It is interesting to note that for β > a (0) − 1 the value of the D N − Q$_{0}$ form factor computed from (89) turns to be negative for t = 0 $^{5}$. It is explained in [3, 23, 43] that the negative value of the D form factor is intimately related to the spontaneous breaking of chiral symmetry in QCD. Some arguments in favor of the negative sign of the D form factor are also presented in [44] in the framework of the simple model of very large nucleus. In this case the first coefficient of the Gegenbauer expansion of the D form factor can be related to the surface tension of the hadron medium and its negative sign follows from the requirement of the mechanical stability of the system. Thus, at this point our model turns to be consistent with the achieved theoretical understanding of the underlying physical picture. Finally it is interesting to note that asymptotic behavior of the D form factor D N − $^{Q$_{0}$}$( t ) for − t → ∞ is power like: This simple exercise shows the power of the analyticity assumptions allowing to unambi- guity fix the subtraction constant in the dispersion relation (81) in terms of the absorptive part of the amplitude. The value of the D form factor turns to be determined by the small ξ asymptotic behavior of the DVCS cross section. It is extremely important to check whether this scenario is consistent with the available experimental data. In this paper we consider the application of the dual para-metrization approach to the case of gluon GPDs in a nucleon. We construct the partial wave expansion for both unpolar- ized and polarized gluon GPDs in the nucleon and present the explicit form of the integral transform allowing to rigorously sum up these formal series. We present the expressions for the elementary leading order amplitude entering the description of hard exclusive meson VII. CONCLUSIONS D N − $^{Q$_{0}$}$( t ) = C N − $^{Q$_{0}$}$(0) 1 α ( α − 1) Γ(1 + β )Γ ( − a ( t ) + 2) Γ (1 + β a ( t )) . (89) D N − $^{Q$_{0}$}$( t ) ∼ ( − t $_{)}$− β $^{+1}$. (90) 27 5 One may check that the contribution of Q 0 (84) into the D - form factor is also a small negative number.