Building Blocks for Subleading Helicity Operators

TL;DR

This paper introduces a comprehensive set of scalar helicity building blocks for constructing subleading power operators in SCET, enhancing the understanding of amplitude behavior near singular phase space regions.

Contribution

It provides the first complete set of scalar helicity building blocks for all orders in SCET power expansion, along with an angular momentum selection rule.

Findings

Complete scalar helicity building blocks for SCET operators

Application of helicity methods to subleading power operators

Angular momentum selection rule for operator assembly

Abstract

On-shell helicity methods provide powerful tools for determining scattering amplitudes, which have a one-to-one correspondence with leading power helicity operators in the Soft-Collinear Effective Theory (SCET) away from singular regions of phase space. We show that helicity based operators are also useful for enumerating power suppressed SCET operators, which encode subleading amplitude information about singular limits. In particular, we present a complete set of scalar helicity building blocks that are valid for constructing operators at any order in the SCET power expansion. We also describe an interesting angular momentum selection rule that restricts how these building blocks can be assembled.