Pomeron loop and running coupling effects in high energy QCD evolution

TL;DR

This paper investigates how the running of the coupling constant affects high-energy QCD evolution with Pomeron loops, showing that it significantly suppresses fluctuations and supports the use of mean-field models like BK for relevant energies.

Contribution

It demonstrates that running coupling effects greatly reduce particle number fluctuations in high-energy QCD evolution with Pomeron loops, validating mean-field approximations for practical energies.

Findings

Particle fluctuations are suppressed by at least an order of magnitude with running coupling.

Running coupling slows down the evolution, affecting the formation of the saturation front.

Mean-field models remain reliable for energies relevant to deep inelastic scattering and forward particle production.

Abstract

Within the framework of a (1+1)-dimensional model which mimics evolution and scattering in QCD at high energy, we study the influence of the running of the coupling on the high-energy dynamics with Pomeron loops. We find that the particle number fluctuations are strongly suppressed by the running of the coupling, by at least one order of magnitude as compared to the case of a fixed coupling, for all the rapidities that we have investigated, up to Y=200. This reflects the slowing down of the evolution by running coupling effects, in particular, the large rapidity evolution which is required for the formation of the saturation front via diffusion. We conclude that, for all energies of interest, processes like deep inelastic scattering or forward particle production can be reliably studied within the framework of a mean-field approximation (like the Balitsky-Kovchegov equation) which includes running coupling effects.