SIMULATION OF QCD INITIAL-STATE RADIATION AT SMALL X

We present the results of Monte Carlo simulations of initial-state gluon radiation in deep inelastic processes in the semi-hard region x --> 0. Specifically, we compare and contrast the results of a recently proposed approach based on the all-loops leading-logarithmic treatment with those of a conventional branching algorithm based on the one-loop Altarelli-Parisi equations. For this study, the evolution of purely gluonic initial states in the region x > 10(-5), Q2 < 10(5) GeV2 was investigated. The two approaches give similar results in this region for highly inclusive observables such as the gluon structure function, but differ on less inclusive properties of the emitted radiation. In particular, the multiplicity of emitted gluons is increased and large rapidity gaps are suppressed in the all-loops treatment. This is due to the larger available phase space and to the new form factor corresponding to non-Sudakov virtual corrections.