Singlet structure function F1 in double-logarithmic approximation

by Prof. Boris Ermolaev (Ioffe Phys. Tech. Inst.)

Monday 3 Dec 2018, 16:30 → 17:30 Europe/Rome

2N22 (Dipertimento di Fisica, M.S. Angelo)

The conventional ways to calculate the perturbative component of the DIS singlet structure function F1 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) contriutions unrelated to 1 / x and because of that they were disregarded as negligibly small. We calculate the singlet F1 in the double-logarithmic approximation (DLA) and account at the same time for the running 𝛼𝑠 effects. We start with a total resummation of both quark and gluon DL contributions and obtain the explicit expression for 𝐹1 in DLA. Then, applying the saddle-point method, we calculate the small-x asymptotics of 𝐹1 , which proves to be of the Regge form with the leading singularity 𝜔0=1.066 . 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 𝐹1 scales: it depends on a single variable 𝑄2/𝑥2 only instead of x and 𝑄2 separately. Finally, we show that the small-x asymptotics reliably represent 𝐹1 at 𝑥≤10−6 .