Has HERA reached a new QCD regime?

TL;DR

This paper reviews HERA data indicating a potential new QCD regime characterized by high gluon densities, with findings consistent with high density QCD predictions and a model explaining deviations from traditional DGLAP evolution.

Contribution

It provides evidence supporting the existence of a new QCD regime at HERA and offers a model that naturally describes deviations from standard DGLAP evolution.

Findings

HERA data show a large gluon structure function

No contradictions with high density QCD predictions

A model explains deviations from DGLAP

Abstract

These notes are a summary of our efforts to answer the question in the title. Our answer is in the affirmative as: (i) HERA data indicate a large value of the gluon structure function; (ii) no contradictions with the asymptotic predictions of high density QCD have been observed; and (iii) the numerical estimates of our model give a natural description of the size of deviation from the routine DGLAP explanation. We discuss the alternative approaches and possible new experiments.