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The ab initio understanding of hadronic three-body systems above threshold, such as exotic resonances or the baryon spectrum, requires the mapping of the finite-volume eigenvalue spectrum, produced in lattice QCD calculations, to the infinite volume. We present the first application of such a formalism to a physical system in form of three interacting positively charged pions. The results for the ground state energies agree with the available lattice QCD results by the NPLQCD collaboration at unphysical pion masses. Extrapolations to physical pion masses are performed using input from effective field theory. The excited energy spectrum is predicted. This demonstrates the feasibility to determine three-body amplitudes above threshold from lattice QCD, including resonance properties of axial mesons, exotics, and excited baryons. [ABSTRACT FROM AUTHOR]

The ρ(770) meson is the most extensively studied resonance in lattice QCD simulations in two (Nƒ=2) and three (Nƒ=2+1) flavor formulations. We analyze Nƒ=2 lattice scattering data using unitarized chiral perturbation theory, allowing not only for the extrapolation in mass but also in flavor, Nƒ=2→Nƒ=2+1. The flavor extrapolation requires information from a global fit to ππ and πK phase shifts from experiment. While the chiral extrapolation of Nƒ=2 lattice data leads to masses of the ρ(770) meson far below the experimental one, we find that the missing KK¯ channel is able to explain this [ABSTRACT FROM AUTHOR]

Hadronic resonances emerge from strong interactions encoding the dynamics of quarks and gluons. The structure of these resonances can be probed by virtual photons parametrized in transition form factors. In this study, twelve N^{*} and Δ transition form factors at the pole are extracted from data with the center-of-mass energy from πN threshold to 1.8 GeV, and the photon virtuality 0≤Q^{2}/GeV^{2}≤8. For the first time, these results are determined from a simultaneous analysis of more than one state, i.e., ∼10^{5}  πN, ηN, and KΛ electroproduction data. In addition, about 5×10^{4} data in the hadronic sector as well as photoproduction serve as boundary conditions. For the Δ(1232) and N(1440) states our results are in qualitative agreement with previous studies, while the transition form factors at the poles of some higher excited states are estimated for the first time. Realistic uncertainties are determined by further exploring the parameter space.

Resonant hadronic systems often exhibit a complicated decay pattern in which three-body dynamics play a relevant or even dominant role. In this work we focus on the a_{1}(1260) resonance. For the first time, the pole position and branching ratios of a three-body resonance are calculated from lattice QCD using one-, two-, and three-meson interpolators and a three-body finite-volume formalism extended to spin and coupled channels. This marks a new milestone for ab initio studies of ordinary resonances along with hybrid and exotic hadrons involving three-body dynamics.

The analysis of the gammap-->etapi(0)p reaction has been performed using data from the GRAAL experiment. The total and differential cross sections and the beam asymmetry have been obtained from threshold up to 1.5 GeV of beam energy. The two resonances S11(1535) and Delta(1700) are expected to be excited in the intermediate states of this reaction. The results are used to test predictions based on the assumption that both resonances are dynamically generated from the meson-baryon interaction provided by chiral Lagrangians. The term involving the Delta(1700) excitation, followed by the decay into etaDelta(1232), is found to be dominant.