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.The spectrum of hadronic excitations observed at accelerator facilities around the world manifests the fundamental interactions of elementary quarks and gluons, governed by the quantum field theory of quantum chromodynamics (QCD). Understanding the complex emergent phenomena of this field theory has captivated the attention of theoretical physicists for more than four decades.Of particular interest is the unusual nature of the lowestlying excitation of the Lambda baryon [1-8] the "Lambda 1405," Λ(1405). The Lambda baryon is a neutral particle, like the neutron, composed of the familiar up (u) and down (d) quarks together with a strange quark (s).For almost 50 years the structure of the Λ(1405) resonance has been a mystery. Even though it contains a relatively massive strange quark and has odd parity, both of which should increase its mass, it is, in fact, lighter than any other excited spin-1/2 baryon. Identifying the explanation for this observation has challenged theorists since its discovery in the 1960s through kaon-proton [1] and pion-proton production [2] experiments.While the quantum numbers of the Λ(1405) can be described by three quarks, (uds), its totally unexpected position in the spectrum has rendered its structure quite mysterious [9]. Before the quark model had been established, Dalitz and co-workers [10,11] speculated that it might be a molecular state of an antikaon, K, bound to a nucleon, N . Whereas the πΣ energy threshold is well below the Λ(1405) resonance position the KN energy threshold is only slightly above. A molecular KN bound state with a small amount of binding energy presents an interesting candidate for the structure of the Λ(1405). Although the intervening years have seen enormous effort devoted to this resonance [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], there has been no convincing resolution.Herein, we present the very first lattice QCD calculation of the electromagnetic form factors of the Λ(1405). This calculation reveals the vanishing of the...

The odd-parity ground state of the Λ baryon lies surprisingly low in mass. At 1405 MeV, it lies lower than the odd-parity ground-state nucleon, even though it has a valence strange quark. Using the PACS-CS (2+1)-flavor full-QCD ensembles, we employ a variational analysis using source and sink smearing to isolate this elusive state. For the first time we reproduce the correct level ordering with respect to nearby scattering thresholds. With a partially quenched strange quark to produce the appropriate kaon mass, we find a low-lying, odd-parity mass trend consistent with the experimental value.

A determination of the excited energy eigenstates of the nucleon, s = 1 2 , I = 1 2 , N ± , is presented in full QCD using 2 + 1 flavor PACS-CS gauge configurations. The correlation-matrix method is used and is built using standard nucleon interpolators employing smearings at the fermion sources and sinks. We develop and demonstrate a new technique that allows the eigenvectors obtained to be utilized to track the propagation of the intrinsic nature of energy-states from one quark mass to the next. This approach is particularly useful for larger dimension correlation matrices where more near-degenerate energy-states can appear in the spectrum.

We present a study of the pseudoscalar and vector meson form factors, calculated using the Fat-Link Irrelevant Clover (FLIC) action in the framework of Quenched Lattice QCD. Of particular interest is the determination of a negative quadrupole moment, indicating that the ρ meson is not spherically symmetric.

In this work we examine the Fat-Link Irrelevant Clover (FLIC) overlap quark propagator and the gluon propagator on both dynamical and quenched lattices. The tadpole-improved Luscher-Weisz gauge action is used in both cases. The dynamical gauge fields use the FLIC fermion action for the sea quark contribution. We observe that the presence of sea quarks causes a suppression of the mass function, quark renormalization function and gluon dressing function in the infrared. The ultraviolet physics is unaffected.