# Finite-Volume Spectrum of ${\pi }^{+}{\pi }^{+}$ and ${\pi }^{+}{\pi }^{+}{\pi }^{+}$ Systems

Mai, M. (Institute for Nuclear Studies and Department of Physics, The George Washington University, Washington, DC 20052, USA) ; Döring, M. (Institute for Nuclear Studies and Department of Physics, The George Washington University, Washington, DC 20052, USA) (Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA)

13 February 2019

Abstract: 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.

Published in: Physical Review Letters 122 (2019)