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1. The $$\Lambda(1405)$$ from Lattice QCD: Determining the Finite-volume Spectra

   https://doi.org/10.22323/1.453.0131  

   Cid-Mora, Barbara; Bulava, John; Hanlon, Andrew D.; Hörz, Ben; Mohler, Daniel; Morningstar, Colin; Moscoso, Joseph; Nicholson, Amy; Romero-Lopez, Fernando; Skinner, Sarah; et al (May 2024, Pos proceedings of science)

   This work presents technical details of determining the finite-volume energy spectra for the scattering amplitude of the coupled-channel πΣ−K¯N from lattice QCD data. The importance of reliably extracting such spectra lies in the crucial dependence of the hadronic scattering amplitudes analysis on the energy spectrum when using L\"{u}scher's formalism. Results of the methods used are presented and the final finite-volume spectra are shown. The analysis of the scattering amplitude based on these results, exhibits a two-pole structure for the Λ(1405), a virtual bound state below the πΣ threshold and a resonance pole right below the K¯N threshold. 

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2. Lattice QCD study of $\pi \mathrm{\Sigma }-\overline{K}N$ scattering and the $\mathrm{\Lambda }\left(1405\right)$ resonance

   https://doi.org/10.1103/PhysRevD.109.014511  

   Bulava, John; Cid-Mora, Bárbara; Hanlon, Andrew D.; Hörz, Ben; Mohler, Daniel; Morningstar, Colin; Moscoso, Joseph; Nicholson, Amy; Romero-López, Fernando; Skinner, Sarah; et al (January 2024, Physical Review D)

   A lattice QCD computation of the coupled channel πΣ–¯KN scattering amplitudes in the Λ(1405) region is detailed. Results are obtained using a single ensemble of gauge field configurations with Nf=2+1 dynamical quark flavors and mπ≈200  MeV and mK≈487  MeV. Hermitian correlation matrices using both single baryon and meson-baryon interpolating operators for a variety of different total momenta and irreducible representations are used. Several parametrizations of the two-channel scattering K-matrix are utilized to obtain the scattering amplitudes from the finite-volume spectrum. The amplitudes, continued to the complex energy plane, exhibit a virtual bound state below the πΣ threshold and a resonance pole just below the ¯KN threshold. 

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3. Two-Pole Nature of the Lambda(1405) Resonance from Lattice QCD

   https://doi.org/10.1103/PhysRevLett.132.051901  

   Bulava, John; Cid-Mora, Bárbara; Hanlon, Andrew D.; Hörz, Ben; Mohler, Daniel; Morningstar, Colin; Moscoso, Joseph; Nicholson, Amy; Romero-López, Fernando; Skinner, Sarah; et al (January 2024, Physical Review Letters)

   This Letter presents the first lattice QCD computation of the coupled channel πΣ−¯KN scattering amplitudes at energies near 1405 MeV. These amplitudes contain the resonance Λ(1405) with strangeness S=−1 and isospin, spin, and parity quantum numbers I(JP)=0(1/2−). However, whether there is a single resonance or two nearby resonance poles in this region is controversial theoretically and experimentally. Using single-baryon and meson-baryon operators to extract the finite-volume stationary-state energies to obtain the scattering amplitudes at slightly unphysical quark masses corresponding to mπ≈200  MeV and mK≈487  MeV, this study finds the amplitudes exhibit a virtual bound state below the πΣ threshold in addition to the established resonance pole just below the ¯KN threshold. Several parametrizations of the two-channel K matrix are employed to fit the lattice QCD results, all of which support the two-pole picture suggested by SU(3) chiral symmetry and unitarity. 

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4. The Λ(1405) pole structure from Lattice QCD: A coupled-channel πΣ−KN study

   https://doi.org/10.1051/epjconf/202430301004  

   Bulava, John; Cid-Mora, Bárbara; Hanlon, Andrew D; Hörz, Ben; Mohler, Daniel; Morningstar, Colin; Moscoso, Joseph; Nicholson, Amy; Romero-López, Fernando; Skinner, Sarah; et al (January 2024, EPJ Web of Conferences)

   Hüsken, N; Danilkin, I; Hagelstein, F (Ed.)

   This report summarizes results of the first lattice QCD calculation of coupled-channelπΣ−K¯Nscattering in the Λ(1405) region. This study was carried out using a single CLS ensemble with a heavier-than-physical pion mass m_π≈ 200 MeV and a lighter-than-physical kaon mass m_K>≈ 487 MeV. Once the finite-volume energy spectrum has been reliably extracted, the Lüscher method was employed to obtain scattering amplitudes. Through a variety of parametrizations of the two-channel K-matrix, the final results show a virtual bound state below the πΣ threshold and a resonance right below K¯N. 

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5. Low-lying baryon resonances from lattice QCD

   Bulava, John; Cid-Mora Barbara; Hanlon, Andrew; Hoerz, Ben; Mohler, Daniel; Morningstar, Colin; Moscoso, Joseph; Nicholson, Amy; Romero-Lopez, Fernando; Skinner, Sarah; et al (October 2023, Nuovo cimento B, to appear)

   Recent results studying the masses and widths of low-lying baryon resonances in lattice QCD are presented. The S-wave Nπ scattering lengths for both total isospins I=1/2 and I=3/2 are inferred from the finite-volume spectrum below the inelastic threshold together with the I=3/2 P-wave containing the Δ(1232) resonance. A lattice QCD computation employing a combined basis of three-quark and meson-baryon interpolating operators with definite momentum to determine the coupled channel Σπ-NKbar scattering amplitude in the Λ(1405) region is also presented. Our results support the picture of a two-pole structure suggested by theoretical approaches based on SU(3) chiral symmetry and unitarity. 

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