Physical Review D
In this work we develop a Lorentz-covariant version of the previously derived formalism for relating finite-volume matrix elements to 2 + J → 2 transition amplitudes. We also give various details relevant for the implementation of this formalism in a realistic numerical lattice QCD calculation. Particular focus is given to the role of single-particle form factors in disentangling finite-volume effects from the triangle diagram that arise when J couples to one of the two hadrons. This also leads to a new finite-volume function, denoted G, the numerical evaluation of which is described in detail. As an example we discuss the determination of the ππ+ J → ππ amplitude in the ρ channel, for which the single-pion form factor, Fπ(Q2), as well as the scattering phase, δππ, are required to remove all power-law (mite-volume effects. The formalism presented here holds for local currents with arbitrary Lorentz structure, and we give specific examples of insertions with up to two Lorentz indices.
Original Publication Citation
Baroni, A., Briceno, R. A., Hansen, M. T., & Ortega-Gama, F. G. (2019). Form factors of two-hadron states from a covariant finite-volume formalism. Physical Review D, 100(3), 034511. doi:10.1103/PhysRevD.100.034511
Baroni, Alessandro; Briceño, Raúl; Hansen, Maxwell T.; and Ortega-Gama, Felipe G., "Form Factors of Two-Hadron States From a Covariant Finite-Volume Formalism" (2019). Physics Faculty Publications. 393.