Failure of the collinear expansion in calculation of the induced gluon emission

TL;DR

This paper shows that the collinear expansion method fails for calculating induced gluon emission in high-energy quark interactions with nuclei, revealing errors in previous higher-twist approaches that used this approximation.

Contribution

The paper critically analyzes and demonstrates the failure of the collinear expansion in gluon emission calculations, challenging prior higher-twist methods based on this approximation.

Findings

Collinear expansion fails in gluon emission from fast quarks in eA DIS.

The N=1 rescattering contribution vanishes under collinear approximation.

Previous higher-twist approaches based on collinear expansion are incorrect.

Abstract

We demonstrate that the collinear expansion fails in the case of gluon emission from a fast quark produced in $eA$ DIS. In this approximation the N=1 rescattering contribution to the gluon spectrum vanishes. We show that the higher-twist approach by Guo, Wang and Zhang [4,5] based on the collinear expansion is wrong. The nonzero gluon spectrum obtained in [4,5] is a consequence of unjustified neglecting some important terms in the collinear expansion.