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The quark mass dependence of octet baryon magnetic polarisabilities is examined at the level of individual quark-sector contributions in the uniform background-field approach of lattice QCD. The aim is to understand the direct impact of increasing the mass of a quark flavour on the magnetic polarisability and indirect or environmental effects associated with changing the mass of spectator quarks, insensitive to the background magnetic field. Noting the need to set the electric charge of some quark flavours to zero, a fractionally charged baryon formalism is introduced. We find that increasing the mass of the charged quark flavour directly causes its contribution to the magnetic polarisability to decrease. However, increasing the mass of the spectator quark flavour indirectly acts to increase the magnetic polarisability. To gain a deeper understanding of these effects, we evaluate the predictions of the constituent quark model in this context. While the model provides a compelling explanation for the environmental effect of varying the spectator quark mass, an explanation of the direct mass dependence is more complicated as competing factors combine in the final result. The lattice results indicate the key factor is a reduction in the constituent quark magnetic moment with increasing quark mass, as it governs the strength of the magnetic transition to the nearby decuplet baryon., Comment: 13 pages, 5 figures. arXiv admin note: text overlap with arXiv:2407.01064

There is strong evidence supporting center vortices as underpinning confinement and dynamical chiral symmetry breaking -- the two key features of nonperturbative QCD. In our recent letter [ arXiv:2305.18690 ] we find that dynamical mass generation vanishes upon vortex removal in full QCD with a near-physical quark mass. In this work we extend those results and consider the influence of center vortex removal on the overlap Landau-gauge quark propagator at multiple valence quark masses on the same dynamical QCD ensemble, keeping fixed the near-physical sea quark mass. After carefully applying a smoothing process we also find that dynamical mass generation is reproduced on the corresponding vortex-only fields. This vortex-only dynamical mass shows qualitative agreement with the untouched Monte Carlo gauge field results. The results reported herein lend further credence to the important relationship between dynamical fermions and center vortices and the mediation of nonperturbative phenomena in QCD., Comment: 14 pages, 12 figures

We present an exploratory lattice QCD analysis of the $ \Omega $-baryon spectrum. Using smeared three-quark operators in a correlation matrix analysis, we report masses for the ground, first and second excited states of the $ J^P = 1/2^\pm,\, 3/2^\pm $ spectra across a broad range in the light quark mass. We investigate the parity and spin quantum numbers for the states observed on the lattice, looking to reconcile these with the resonances encountered in experiment. We find that the $ \Omega^-(2012) $ as reported by the Particle Data Group corresponds to two overlapping resonances with $ J^P = 1/2^- $ and $ 3/2^- $. We also propose quantum number assignments for the higher energy resonances, and identify successive radial excitations within the spectra., Comment: 22 pages, 13 figures. arXiv admin note: text overlap with arXiv:2312.11574

Drawing on recent advances in lattice-QCD background-field techniques, the magnetic polarisability of octet baryons is calculated from the first principles of QCD. The results are presented in the context of new constituent quark-model calculations providing a framework for understanding the lattice results and a direct comparison with simulation results at unphysical quark masses. Using smeared quark sources, low-lying Laplacian eigenmode projection and final-state Landau mode projection, considerable attention is devoted to ensuring single-state isolation in the lattice correlation functions. We also introduce new weighting methods to reduce the sensitivity to correlation-function fits, averaging over many fits based on merit drawn from the full correlated $\chi^2$ of the fits. The techniques are implemented on the $32^3 \times 64$, 2+1-flavour dynamical-fermion lattices provided by the PACS-CS collaboration following the introduction of uniform magnetic fields quantised to the lowest nontrivial values available. After some fine tuning of the constituent quark model parameters, we find the model captures the patterns observed in the lattice QCD results very well, providing important insights into the physics underpinning the magnetic polarisabilities. Finally, comparison with the most recent results from experiment proceeds through an effective field theory formalism which incorporates estimates of finite-volume corrections and small electro-quenching corrections as the results are brought to the physical point. We find excellent agreement with experiment where available, including the proton and neutron polarisabilities., Comment: 32 pages, 15 figures

The geometry of centre vortices is studied in $\mathrm{SU(3)}$ gauge theory at finite temperature to capture the key structural changes that occur through the deconfinement phase transition. Visualisations of the vortex structure in temporal and spatial slices of the lattice reveal a preference for the vortex sheet to align with the temporal dimension above the critical temperature. This is quantified through a correlation measure. A collection of vortex statistics, including vortex and branching point densities, and vortex path lengths between branching points, are analysed to highlight internal shifts in vortex behaviour arising from the loss of confinement. We find the zero-temperature inclination of branching points to cluster at short distances vanishes at high temperatures, embodying a rearrangement of branching points within the vortex structure. These findings establish the many aspects of centre vortex geometry that characterise the deconfinement phase transition in pure gauge theory., Comment: 26 pages, 25 figures including 5 interactive animations, version accepted for publication

The parity-expanded variational analysis (PEVA) technique enables the isolation of opposite-parity eigenstates at finite momentum. The approach has been used to perform the first lattice QCD calculations of excited-baryon form factors. In particular, these calculations show that the low-lying odd-parity nucleon excitations are described well by constituent quark models at moderate u and d quark masses approaching the strange quark mass. Herein, we extend the PEVA technique to establish a formalism for the determination of odd-parity nucleon electromagnetic transition form factors in lattice QCD. The formalism is implemented in the first calculation of the helicity amplitudes for transitions from the ground state nucleon to the first two odd-parity excitations. Through a comparison with constituent quark model calculations of these amplitudes, these new results give important insight into the structure of these excitations. This work is a critical step towards confronting experimental electroproduction amplitudes for the $N^*(1535)$ and $N^*(1650)$ resonances with ab-initio lattice QCD calculations., Comment: 14 pages, 12 figures

This presentation opens with a brief review of lattice QCD calculations showing the $2s$ radial excitation of the nucleon sits at approximately 2 GeV, well above the Roper resonance position. We then proceed to reconcile this observation with experimental scattering data. While the idea of dressing quark-model states in a coupled-channel analysis to describe scattering data has been around for decades, it's now possible to bring these descriptions to the finite-volume of lattice QCD for confrontation with lattice-QCD calculations. This combination of lattice QCD and experiment demands that we reconsider our preconceived notions about the quark-model and its excitation spectrum. We close with a discussion of an unanticipated resolution to the missing baryon resonances problem., Comment: 8 pages, 2 figures. To appear as a plenary contribution to the proceedings of HADRON 2023, the 20th International Conference on Hadron Spectroscopy and Structure, 5th-9th June 2023, Genova, Italy