One-loop renormalization and the S-matrix

TL;DR

This paper explores the structure of one-loop amplitudes in four-dimensional massless theories, revealing how bubble coefficients relate to UV behavior and beta functions through on-shell amplitude analysis and recursion relations.

Contribution

It uncovers a hidden structure in bubble coefficients that explains their cancellations and links them to the beta function in Yang-Mills theory using on-shell methods.

Findings

Bubble coefficients encode UV divergences and beta functions.

Hidden collinear pole structures cause systematic cancellations.

Recursion relations confirm the generality of the results.

Abstract

In four-dimensional theories with massless particles, the one-loop amplitudes can be expressed in terms of a basis of scalar integrals and rational terms. Since the scalar bubble integrals are the only UV divergent integrals, the sum of the bubble coefficients captures the 1-loop UV behavior. In particular, in a renormalizable theory the sum of the bubble coefficients equals the tree-level amplitude times a proportionality constant that is related to the one-loop beta function coefficient beta_0. In this paper, we study how this proportionality is achieved from the viewpoint of on-shell amplitudes. For n-point MHV amplitude in (super) Yang-Mills theory, we demonstrate the existence of a hidden structure in each individual bubble coefficient which directly leads to systematic cancellations within the sum of them. The origin of this structure can be attributed to the collinear poles within a two-particle cut. Due to the cancellation, the one-loop beta function coefficient can be identified as a sum over the residues of unique collinear poles in particular two-particle cuts. Using CSW recursion relations, we verify the generality of this statement by reproducing the correct proportionality factor from such cuts for n-point split-helicity N^kMHV amplitudes.