Soft gluons and superleading logarithms in QCD

TL;DR

This paper explores the complex behavior of soft gluons in QCD, revealing that factorization breaks down at certain scales and leads to unexpected double logarithmic effects in dijet production, with implications for high-energy collision predictions.

Contribution

It introduces the prediction of superleading logarithms in dijet production due to factorization failure at high scales in QCD.

Findings

Factorization of collinear emissions fails above the veto scale.

Double logarithms appear at fourth order in perturbation theory.

The effect is subleading in the number of colors.

Abstract

After a brief introduction to the physics of soft gluons in QCD we present a surprising prediction. Dijet production in hadron-hadron collisions provides the paradigm, i.e. h_1 +h_2 \to jj+X. In particular, we look at the case where there is a restriction placed on the emission of any further jets in the region in between the primary (highest p_T) dijets. Logarithms in the ratio of the jet scale to the veto scale can be summed to all orders in the strong coupling. Surprisingly, factorization of collinear emissions fails at scales above the veto scale and triggers the appearance of double logarithms in the hard sub-process. The effect appears first at fourth order relative to the leading order prediction and is subleading in the number of colours.