Singlet structure function [Formula omitted] in double-logarithmic approximation

The conventional ways to calculate the perturbative component of the DIS singlet structure function [Formula omitted] involve approaches based on BFKL which account for the single-logarithmic contributions accompanying the Born factor 1 / x. In contrast, we account for the double-logarithmic (DL) contributions unrelated to 1 / x and because of that they were disregarded as negligibly small. We calculate the singlet [Formula omitted] in the double-logarithmic approximation (DLA) and account at the same time for the running [Formula omitted] effects. We start with a total resummation of both quark and gluon DL contributions and obtain the explicit expression for [Formula omitted] in DLA. Then, applying the saddle-point method, we calculate the small-x asymptotics of [Formula omitted], which proves to be of the Regge form with the leading singularity [Formula omitted]. Its large value compensates for the lack of the factor 1 / x in the DLA contributions. Therefore, this Reggeon can be identified as a new Pomeron, which can be quite important for the description of all QCD processes involving the vacuum (Pomeron) exchanges at very high energies. We prove that the expression for the small-x asymptotics of [Formula omitted] scales: it depends on a single variable [Formula omitted] only instead of x and [Formula omitted] separately. Finally, we show that the small-x asymptotics reliably represent [Formula omitted] at [Formula omitted].