The subtraction constant is given by the value of the amplitude at the non-physical point ω = 0 ( ξ = ∞ ). It is known to be fixed by the D -term and equals 2 D $^{g}$( t ). In [12, 13, 32] it was suggested to fix the subtraction constant in the dispersion relation (53) in terms of the imaginary part of the corresponding elementary amplitude assuming special analytical properties in j of the function For entire odd j ≥ 1 (54) defines in the family of sum rules for the specific combinations of coefficients h g ( E ) 2 ν + j, 2 ν at powers of ξ of the Mellin moments of GPD H g ( E ) (see eq. (22) for the definition). For j = − 1 the integral is divergent since it is usually assumed that 1 $_{x}$( H g ( E $^{)}$( x, x, t ) − H g ( E $^{)}$( x, 0 , t )) ∼ 1 /x α with α ∼ 1. In order to provide the desired ex- pression for the D - form factor (54) is to be properly analytically continued to j = − 1. To make it explicitly, let us assume that 1 $_{x}$( H g ( E $^{)}$( x, x, t ) − H g ( E $^{)}$( x, 0 , t )) belong to the class of functions with power like behavior for x ∼ 0, which can be presented as the finite sums of singular terms [40]: We suppose that for all r = 1 , ...R α$_{r}$ < 2 and f$_{r}$ ( x ) are arbitrary functions of x infinitely differentiable in the vicinity of x = 0. It is also supposed that f$_{r}$ ( x ) have zeroes of a sufficiently high order for x = 1. Then the relation for the gluon D form factor reads as in [12]: The lower integration limit “(0)” in (56) symbolize that we use the so-called analytic (or canonical) regularization [40]: In the framework of the dual parametrization assuming that N g ( E $^{)}$( x, t ) and G ( E ) 0 ( x, t ) also belong to class (55) (see discussion in [22]) one may rewrite the sum rule (56) for the 18 Φ( j ) ≡ ∞ ∑ ν =0 h g ( E ) 2 ν + j, 2 $_{ν}$( t ) = ∫ 1 0 dx x $_{j}$1 x [ H g ( E $^{)}$( x, x, t ) − H g ( E $^{)}$( x, 0 , t ) ] . (54) F : F ( x ) = R ∑ r =1 1 x $_{α$_{r}$}$f$_{r}$ ( x ) . (55) 2 D $^{g}$( t ) = ∞ ∑ ν =0 h g ( E ) 2 ν − 1 , 2 $_{ν}$( t ) = ∫ 1 (0) dx 1 x · 1 x [ H g ( E $^{)}$( x, x, t ) − H g ( E $^{)}$( x, 0 , t ) ] . (56) ∫ 1 (0) dx f ( x ) x 1+ α = ∫ 1 0 dx 1 x 1+ α [ f ( x ) − f (0) − $^{$_{xf}$′$_{(0)]}$}$− f (0) 1 α − $_{f}$′$_{(0)}$ 1 α − 1 (for α < 2) . (57)