Pomeron loop and running coupling effects in high energy QCD evolution

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.

Asymptotics of QCD traveling waves with fluctuations and running coupling effects

“…It remains to study if such a large Y f orm is specific to that model, or occurs also in QCD. The results of [60] and of the present study seem however to be compatible concerning the asymptotic behavior of the cumulants of the saturation scale. Note also that the model used in [60] is a one-dimensional model with similar assumptions concerning the fluctuation term as the one studied here.…”

“…While completing this work, results of the numerical simulation [60] concerning the extension with running coupling of a 1+1 dimensional reaction-diffusion model [51] for high energy QCD have appeared. The main result of [60] is that fluctuations effects are very strongly suppressed in the running coupling case, up to a quite high rapidity.…”

“…The main result of [60] is that fluctuations effects are very strongly suppressed in the running coupling case, up to a quite high rapidity. Indeed, Y f orm is found to be large in that toy model, of the order of a few hundreds, and thus beyond the reach of experiments.…”

“…I also thank Edmond Iancu for insightful discussions, in particular about the results of [60] before publication. I also acknowledge Al Mueller and Gregory Soyez for useful remarks.…”

Color glass condensate and its relation to HERA physics

“…However, in practice, this is not a serious drawback, since these correlations are anyway suppressed by the running of the coupling [36]. This will be further discussed in the next section.…”