An Operator Product Expansion for Form Factors III. Finite Coupling and Multi-Particle Contributions

TL;DR

This paper develops a bootstrap approach to compute finite-coupling form factors in planar N=4 super-Yang-Mills theory, introducing new building blocks called form factor transitions and matching predictions with perturbative data.

Contribution

It introduces a novel bootstrap method for form factor transitions at finite coupling, extending the operator product expansion framework for form factors.

Findings

Computed form factor transitions using bootstrap techniques.

Predicted the leading and subleading collinear expansion terms at finite coupling.

Achieved perfect agreement with existing perturbative data.

Abstract

Form factors in planar $\mathcal{N}=4$ super-Yang-Mills theory have a dual description in terms of periodic Wilson loops. This duality maps the multi-collinear expansion of the former to an operator product expansion of the latter. The coefficients of this expansion are decomposed in terms of several elementary building blocks and can be determined at finite 't Hooft coupling using bootstrap and integrability techniques. Some of these blocks are known from an analogous expansion of scattering amplitudes. In addition to these, the expansion for form factors includes a new type of building block, called {\it form factor transitions}, that encode information about the local operator. In the present paper, we consider the form factor of the chiral part of the stress-tensor supermultiplet. We bootstrap the corresponding form factor transitions of two-particle flux-tube states and use them to predict the leading term in the collinear expansion at finite coupling. The transitions we find can be expressed in terms of a quantity that previously appeared in a seemingly unrelated context, namely the octagon kernel. Lastly, we use a factorized ansatz to determine the multi-particle form factor transitions at finite coupling, which we use to predict the first subleading term in the collinear expansion. A perfect match is found between our predictions and the available perturbative data.