Infrared singularities of scattering amplitudes in perturbative QCD
Abstract
An exact formula is derived for the infrared singularities of dimensionally regularized scattering amplitudes in massless QCD with an arbitrary number of legs, valid at any number of loops. It is based on the conjecture that the anomalousdimension matrix of njet operators in softcollinear effective theory contains only a single nontrivial color structure, whose coefficient is the cusp anomalous dimension of Wilson loops with lightlike segments. Its colordiagonal part is characterized by two anomalous dimensions, which are extracted to threeloop order from known perturbative results for the quark and gluon form factors. This allows us to predict the threeloop coefficients of all 1/epsilon^k poles for an arbitrary nparton scattering amplitudes, generalizing existing twoloop results.
 Authors:
 Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
 Johannes GutenbergUniversitaet Mainz, Mainz (Germany)
 Publication Date:
 Research Org.:
 Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
 Sponsoring Org.:
 USDOE Office of Science (SC), High Energy Physics (HEP) (SC25)
 OSTI Identifier:
 1155694
 Report Number(s):
 MZTH0901
Journal ID: ISSN 00319007; PRLTAO; ArticleNumber: 199905
 DOE Contract Number:
 AC0207CH11359
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physical Review Letters; Journal Volume: 111; Journal Issue: 19
 Country of Publication:
 United States
 Language:
 English
 Subject:
 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Citation Formats
Becher, Thomas, and Neubert, Matthias. Infrared singularities of scattering amplitudes in perturbative QCD. United States: N. p., 2013.
Web. doi:10.1103/PhysRevLett.111.199905.
Becher, Thomas, & Neubert, Matthias. Infrared singularities of scattering amplitudes in perturbative QCD. United States. doi:10.1103/PhysRevLett.111.199905.
Becher, Thomas, and Neubert, Matthias. Fri .
"Infrared singularities of scattering amplitudes in perturbative QCD". United States.
doi:10.1103/PhysRevLett.111.199905. https://www.osti.gov/servlets/purl/1155694.
@article{osti_1155694,
title = {Infrared singularities of scattering amplitudes in perturbative QCD},
author = {Becher, Thomas and Neubert, Matthias},
abstractNote = {An exact formula is derived for the infrared singularities of dimensionally regularized scattering amplitudes in massless QCD with an arbitrary number of legs, valid at any number of loops. It is based on the conjecture that the anomalousdimension matrix of njet operators in softcollinear effective theory contains only a single nontrivial color structure, whose coefficient is the cusp anomalous dimension of Wilson loops with lightlike segments. Its colordiagonal part is characterized by two anomalous dimensions, which are extracted to threeloop order from known perturbative results for the quark and gluon form factors. This allows us to predict the threeloop coefficients of all 1/epsilon^k poles for an arbitrary nparton scattering amplitudes, generalizing existing twoloop results.},
doi = {10.1103/PhysRevLett.111.199905},
journal = {Physical Review Letters},
number = 19,
volume = 111,
place = {United States},
year = {Fri Nov 01 00:00:00 EDT 2013},
month = {Fri Nov 01 00:00:00 EDT 2013}
}

An exact formula is derived for the infrared singularities of dimensionally regularized scattering amplitudes in massless QCD with an arbitrary number of loops and legs. It is based on the conjecture that the anomalousdimension matrix of njet operators in softcollinear effective theory is fully determined by three functions of {alpha}{sub s}, which can be extracted from known perturbative results for the quark and gluon form factors. This allows us to predict the threeloop coefficients of all 1/{epsilon}{sup k} poles for arbitrary nparton scattering amplitudes, generalizing existing twoloop results.

Infrared singularities of QCD amplitudes with massive partons
A formula for the twoloop infrared singularities of dimensionally regularized QCD scattering amplitudes with an arbitrary number of massive and massless legs is derived. The singularities are obtained from the solution of a renormalizationgroup equation, and factorization constraints on the relevant anomalousdimension matrix are analyzed. The simplicity of the structure of the matrix relevant for massless partons does not carry over to the case with massive legs, where starting at twoloop order new color and momentum structures arise, which are not of the colordipole form. The resulting twoloop threeparton correlations can be expressed in terms of two functions, for whichmore » 
Quark distribution amplitudes for the nucleon from perturbative QCD and QCD sum rules
We discuss quark distribution amplitudes for the nucleon obtained from perturbative QCD in connection with QCD sum rules on the light cone. Because of nonperturbative contributions these amplitudes have a complex nonsmooth structure and are dominated by strong correlations at the edges of the phase space. The antisymmetric part of the mixed symmetry amplitudes is found to be enhanced. 
{chi}{sub {ital c}2}{r_arrow}{rho}{rho} and the {rho} polarization in massless perturbative QCD: How to test the distribution amplitudes
We compute the helicity density matrix of {rho} vector mesons produced in the twobody decays of polarized {chi}{sub {ital c}2}{close_quote}s in the framework of massless perturbative QCD. The {chi}{sub {ital c}2}{close_quote}s are either exclusively or inclusively produced in {ital p{bar p}} or {ital pp} interactions, via quarkantiquark annihilation or gluon fusion. Our results show unambiguous significant differences depending on the choice of the {rho} distribution amplitudes and allow us to discriminate between different proposed models. {copyright} {ital 1996 The American Physical Society.}