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# The 39th International Symposium on Lattice Field Theory (Lattice 2022)

Aug 8 – 13, 2022
Hörsaalzentrum Poppelsdorf
Europe/Berlin timezone

## Resonance form factors from finite-volume correlation functions with the external field method

Aug 9, 2022, 4:50 PM
20m
CP1-HSZ/1st-1.002 - HS6 (CP1-HSZ)

50

### Speaker

Jonathan Lozano de la Parra (uni-bonn)

### Description

The study of resonance form factors in lattice QCD is a challenging endeavor. Namely, the infinite-volume limit, $L \rightarrow \infty$, is not well defined in the matrix element (here, $L$ is the spacial extension of a rectangular lattice). This irregular behavior persists even after multiplying each external leg with the pertinent Lellouch-Lüscher factor and stems from the so-called triangle diagram.

In this talk, I shall discuss a novel method to tackle this problem in which the difficulty, related to the presence of the triangle diagram, never emerges. The approach is based on the study of two-particle scattering in a static, spatially periodic external field by using a generalization of the Lüscher method in the presence of such a field. In addition, I shall demonstrate that the resonance form factor in the Breit frame is given by the derivative of a resonance pole position in the complex plane with respect to the coupling constant of the external field. This result is a generalization of the well-known Feynman-Hellmann theorem for the form factor of a stable particle.

### Primary authors

Jonathan Lozano de la Parra (uni-bonn) Fernando Romero-Lopez (MIT) Ulf-G. Meißner (Helmholtz-Institut für Strahlen- und Kernphysik) Akaki Rusetsky (Helmholtz-Institut für Strahlen- und Kernphysik) Gerrit Schierholz (DESY)