Speaker
Description
The $\Lambda(1405)$ baryon is not well described by the naive three-quark picture and has long been interpreted as a $\bar{K}N$ quasi-bound state. To study it from first principles, we compute the underlying meson-baryon interactions in lattice QCD with the HAL QCD method, in which hadron interactions are extracted as potentials. We work in the flavor SU(3) limit, where each irreducible representation becomes almost a single channel, so that the interaction can be understood in its simplest form. At a pseudo-scalar meson mass $m_M \approx 670$ MeV, we calculate the potentials in the singlet and two octet channels, in which the chiral unitary model predicts the poles corresponding to the $\Lambda(1405)$. The leading-order potentials in the derivative expansion exhibit singular behavior, which prevents a reliable extraction of observables. We therefore replace the standard local approximation by a separable potential. The separable potentials show attraction strong enough to produce bound states. In this talk, we present the resulting binding energies with their statistical and systematic uncertainties, and discuss them in the light of the mass hierarchy suggested by the chiral unitary model.