where c q > 0 is the numerical constant. The value of the intercept in the relevant kinematical domain is α ( Q 2 = 4GeV $^{2}$) = 1 . 1 ÷ 1 . 2, The slope parameter α ′ can be fixed e.g. with the help of the form factor sum rule [39]: α ′ = 1 . $_{1 GeV}$− $^{2}$. The alluring possibility is to take advantage of the opportunities provided by the Abel transform tomography method and instead of modelling GPD quintessence function employ a model for the imaginary part of the elementary amplitude Im A ( ξ, t ). The real part of the elementary amplitude Re A ( ξ, t ) can be then computed with the help of GPD quintessence restored from Im A ( ξ, t ) using the tomography method. The important advantage of this approach is that the amplitude computed in this way possess proper analytic properties in ξ and automatically satisfies the fixed t dispersion relation with one subtraction in the variable ω = 1 ξ [33, 37]: since the expression for Re A ( ξ, t ) in the dual parametrization through the GPD quintessence function is equivalent to the the dispersion relation (81). Let us introduce the following notations: Im A Q$_{0}$ and Im A N − Q$_{0}$ for the contributions to the imaginary part originating from Q$_{0}$ ( x, t ) and N ( x, t ) − Q$_{0}$ ( x, t ) respectively. Analogously for the D form factor we introduce the notations D Q$_{0}$ and D N − $^{Q$_{0}$}$. The leading singular behavior of Im A $^{Q$_{0}$}$( ξ, t ) computed from the Q$_{0}$ ( x, t ) corresponding to t -dependent PDF q ( x, t ) with the asymptotic behavior (80) is where we define the function The contribution of Q$_{0}$ to the D form factor can be computed using The skewness effect in the model which includes only the contribution of Q$_{0}$ is given by the conformal ratio (75). In order to make skewness effect satisfy H1 measurements [41] we 25 A ( ξ, t ) = 4 D ( t ) + 1 π ∫ 1 0 $_{dξ}$′ ( 1 ξ − ξ ′ − iϵ − 1 ξ + ξ ′ − iϵ ) Im A ( $_{ξ}$′ − iϵ, t ) , (81) Im A $^{Q$_{0}$}$( ξ, t ) ∼ c q 2 a ( t )+1 ξ a ( t ) Γ( 1 $_{2}$)Γ( a ( t ) + 3 $_{2}$) Γ( a ( t ) + 2) ≡ C $^{Q$_{0}$}$( t ) 1 ξ a ( t ) , (82) C $^{Q$_{0}$}$( t ) ≡ c q 2 a ( t $^{)+1}$Γ( 1 $_{2}$)Γ( a ( t ) + 3 $_{2}$) Γ( a ( t ) + 2) C $^{Q$_{0}$}$(0) ≃ 3 π 2 c q for α ≈ 1 . (83) D $^{Q$_{0}$}$( t ) = ∫ 1 0 dx x Q$_{0}$ ( x, t ) ( 1 √$_{1 +}$ x 2 − 1 ) . (84)