The SU(2|3) dynamic two-loop form factors

TL;DR

This paper calculates two-loop form factors for specific operators in the SU(2|3) sector of N=4 SYM, revealing new insights into transcendentality, operator mixing, and potential links to QCD amplitudes.

Contribution

It provides the first detailed two-loop form factor calculations for non-protected operators in the SU(2|3) sector, including analysis of transcendentality and operator mixing.

Findings

Maximally transcendental part matches that of half-BPS operators.

Discovered connections between subleading transcendentality terms and spin chain densities.

Resolved operator mixing and computed anomalous dimensions at two loops.

Abstract

We compute two-loop form factors of operators in the $SU(2|3)$ closed subsector of $N=4$ supersymmetric Yang-Mills. In particular, we focus on the non-protected, dimension-three operators $\mathrm{Tr} (X[Y,Z])$ and $\mathrm{Tr} ( \psi \psi)$ for which we compute the four possible two-loop form factors, and corresponding remainder functions, with external states $\langle \bar{X} \bar{Y} \bar{Z}|$ and $\langle \bar{\psi} \bar{\psi}|$. Interestingly, the maximally transcendental part of the two-loop remainder of $\langle\bar{X} \bar{Y} \bar{Z}| \mathrm{Tr} (X[Y,Z]) |0\rangle$ turns out to be identical to that of the corresponding known quantity for the half-BPS operator $\mathrm{Tr} (X^3)$. We also find a surprising connection between the terms subleading in transcendentality and certain a priori unrelated remainder densities introduced in the study of the spin chain Hamiltonian in the SU(2) sector. Next, we use our calculation to resolve the mixing, recovering anomalous dimensions and eigenstates of the dilatation operator in the SU(2|3) sector at two loops. We also speculate on potential connections between our calculations in $N=4$ super Yang-Mills and Higgs + multi-gluon amplitudes in QCD in an effective Lagrangian approach.