https://doi.org/10.1140/epjc/s10052-018-5675-6
Regular Article - Theoretical Physics
Singlet structure function 
in double-logarithmic approximation
1
Ioffe Physico-Technical Institute, 194021, St.Petersburg, Russia
2
St.Petersburg Institute of Nuclear Physics, 188300, Gatchina, Russia
* e-mail: boris.ermolaev@cern.ch
Received:
25
September
2017
Accepted:
22
February
2018
Published online:
12
March
2018
The conventional ways to calculate the perturbative component of the DIS singlet structure function 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 in the double-logarithmic approximation (DLA) and account at the same time for the running 
effects. We start with a total resummation of both quark and gluon DL contributions and obtain the explicit expression for in DLA. Then, applying the saddle-point method, we calculate the small-x asymptotics of , which proves to be of the Regge form with the leading singularity 
. 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 scales: it depends on a single variable 
only instead of x and 
separately. Finally, we show that the small-x asymptotics reliably represent at 
.
© The Author(s), 2018
