title: Lattice QCD evidence that the Λ(1405) resonance is an antikaon-nucleon molecule.
abstract: For almost 50 years the structure of the Λ(1405) resonance has been a mystery. Even though it contains a heavy strange quark and has odd parity, its mass is lower than any other excited spin-1/2 baryon. Dalitz and co-workers speculated that it might be a molecular state of an antikaon bound to a nucleon. However, a standard quark-model structure is also admissible. Although the intervening years have seen considerable effort, there has been no convincing resolution. Here we present a new lattice QCD simulation showing that the strange magnetic form factor of the Λ(1405) vanishes, signaling the formation of an antikaon-nucleon molecule. Together with a Hamiltonian effective-field-theory model analysis of the lattice QCD energy levels, this strongly suggests that the structure is dominated by a bound antikaon-nucleon component. This result clarifies that not all states occurring in nature can be described within a simple quark model framework and points to the existence of exotic molecular meson-nucleon bound states.
authors.affiliation: Special Research Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Jonathan M M
authors.initials: JM
authors.lastname: Hall
authors.affiliation: Special Research Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Waseem
authors.initials: W
authors.lastname: Kamleh
authors.affiliation: Special Research Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Derek B
authors.initials: DB
authors.lastname: Leinweber
authors.affiliation: Special Research Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.|National Computational Infrastructure (NCI), Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Menadue
authors.affiliation: Special Research Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Owen
authors.affiliation: Special Research Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.|ARC Centre of Excellence for Particle Physics at the Terascale (CoEPP), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Thomas
authors.affiliation: Special Research Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.|ARC Centre of Excellence for Particle Physics at the Terascale (CoEPP), Department of Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Ross D
authors.initials: RD
authors.lastname: Young