Light Scalar Tetraquarks and Sigma Baryon Spectroscopy from Lattice QCD

The finite-volume QCD spectrum in the I = 1/2 , S = -1, parity-even, zero-momentum sector

containing the k meson and the I = 1, S = 0, parity-even, G-parity-odd, zero-momentum sector containing the a₀(980) meson is studied with the inclusion of tetraquark operators

using lattice QCD. Several hundred tetraquark operators of different flavor, color, and spatial structures are included in this study. We find that the inclusion of tetraquark operators is crucial for determining the spectrum in each sector, and that there is a state in each sector with sizeable tetraquark component that is missed without the use of tetraquark operators. The spectrum of excited sigma baryons in the I = 1, S = -1, parity-even and parity-odd sectors is also studied using large bases of single- and two-hadron operators, for the first time in lattice QCD. We find qualitative agreement with experiment, and near-agreement with a previous study that neglects two-hadron operators. All calculations are performed using 412 gauge field configurations with clover-improved Wilson fermions on a 32³ x 256 anisotropic lattice with m_{π ≈}230 MeV, and quark propagation is treated using the Stochastic LapH method.