Lattice QCD study of the scalar mesons a0(1450) and σ(600)

We study the a0 and σ mesons with the overlap fermion in the chiral regime with the pion mass as low as 182 MeV in the quenched approximation. After the η′π ghost states are separated, we find the a0 mass with the qq̄ interpolation field to be almost independent of the quark mass in the region below the strange quark mass. The chirally extrapolated results are consistent with a0(1450) being the ud̄ meson and K0*(1430) being the us̄ meson with calculated masses at 1.42±0.13GeV and 1.41±0.12GeV, respectively. We also calculate the scalar mesonium with a tetraquark interpolation field. In addition to the two-pion scattering states, we find a state at ∼550MeV. Through the study of volume dependence, we confirm that this state is a one-particle state, in contrast to the two-pion scattering states. This suggests that the observed state is a tetraquark mesonium which is quite possibly the σ(600) meson.