KLT-type relations for QCD and bicolor amplitudes from color-factor symmetry

TL;DR

This paper derives KLT-type relations for tree-level QCD amplitudes with gluons and quark pairs using color-factor symmetry, and introduces the bicolor scalar theory as a new 'zeroth copy' of QCD.

Contribution

It generalizes KLT relations to QCD with quarks and introduces the bicolor scalar theory as a novel framework for amplitude relations.

Findings

Derived explicit KLT-type relations for QCD amplitudes with up to two quark pairs.

Introduced the bicolor scalar theory as a new 'zeroth copy' of QCD.

Established KLT-type relations for biadjoint and bicolor theories using color-factor symmetry.

Abstract

Color-factor symmetry is used to derive a KLT-type relation for tree-level QCD amplitudes containing gluons and an arbitrary number of massive or massless quark-antiquark pairs, generalizing the expression for Yang-Mills amplitudes originally postulated by Bern, De Freitas, and Wong. An explicit expression is given for all amplitudes with two or fewer quark-antiquark pairs in terms of the (modified) momentum kernel. We also introduce the bicolor scalar theory, the "zeroth copy" of QCD, containing massless biadjoint scalars and massive bifundamental scalars, generalizing the biadjoint scalar theory of Cachazo, He, and Yuan. We derive KLT-type relations for tree-level amplitudes of biadjoint and bicolor theories using the color-factor symmetry possessed by these theories.