The Structure of Multiloop Amplitudes in Gauge and Gravity Theories

TL;DR

This paper reviews the duality between color and kinematics in gauge theories, revealing a simple double-copy relation that connects gauge and gravity scattering amplitudes, supported by evidence across all loop orders.

Contribution

It summarizes recent discoveries of the color-kinematics duality and the double-copy construction, including proofs and Lagrangian identifications, advancing understanding of gauge-gravity relations.

Findings

Duality holds to all loop orders

Double-copy relation simplifies gravity amplitude calculations

Identification of gauge theories leading to gravity Lagrangians

Abstract

We review the recently discovered duality between color and kinematics in gauge theories. This duality leads to a remarkably simple double-copy relation between diagrammatic numerators of gravity scattering amplitudes and gauge-theory ones. We summarize nontrivial evidence that the duality and double-copy property holds to all loop orders. We also comment on other developments, including a proof that the gauge-theory duality leads to the gravity double-copy property, and the identification of gauge-theory Lagrangians whose double copies yield gravity Lagrangians.