Physical Review D
This work explores scattering amplitudes that couple two-particle systems via a single external current insertion, 2 + J → 2. Such amplitudes can provide structural information about the excited QCD spectrum. We derive an exact analytic representation for these reactions. From these amplitudes, we show how to rigorously define resonance and bound-state form factors. Furthermore, we explore the consequences of the narrow-width limit of the amplitudes as well as the role of the Ward-Takahashi identity for conserved vector currents. These results hold for any number of two-body channels with no intrinsic spin, and a current with arbitrary Lorentz structure and quantum numbers. This work and the existing finite-volume formalism provide a complete framework for determining this class of amplitudes from lattice QCD.
Original Publication Citation
Briceño, R. A., Jackura, A. W., Ortega-Gama, F. G., & Sherman, K. H. (2021). On-shell representations of two-body transition amplitudes: Single external current. Physical Review D, 103(11), 1-32, Article 114512. https://doi.org/10.1103/PhysRevD.103.114512
0000-0003-1109-1473 (Briceño), 0000-0002-3249-5410 (Jackura)
Briceño, Raúl A.; Jackura, Andrew W.; Ortega-Gama, Felipe G.; and Sherman, Keegan H., "On-Shell Representations of Two-Body Transition Amplitudes: Single External Current" (2021). Physics Faculty Publications. 536.