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Register a new userA Study of Hadron Deformation in Lattice QCD
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We develop the formalism for the evaluation of density-density correlators in lattice QCD that includes techniques for the computation of the all-to-all propagators involved. A novel technique in this context is the implementation of the one-end trick in the meson sector. Density-density correlators provide a gauge invariant definition for the hadron wave function and yield information on hadron deformation. We evaluate density-density correlators using two degenerate flavors of dynamical Wilson fermions for the pion, the rho-meson, the nucleon and the $Delta$. Using the one-end trick we obtain results that clearly show deformation of the rho-meson.
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Recent progress in lattice QCD calculations of nucleon structure will be presented. Calculations of nucleon matrix elements and form factors have long been difficult to reconcile with experiment, but with advances in both methodology and computing resources, this situation is improving. Some calculations have produced agreement with experiment for key observables such as the axial charge and electromagnetic form factors, and the improved understanding of systematic errors will help to increase confidence in predictions of unmeasured quantities. The long-omitted disconnected contributions are now seeing considerable attention and some recent calculations of them will be discussed.
The structure of neutrons, protons, and other strongly interacting particles is now being calculated in full, unquenched lattice QCD with quark masses entering the chiral regime. This talk describes selected examples, including the nucleon axial charge, structure functions, electromagnetic form factors, the origin of the nucleon spin, the transverse structure of the nucleon, and the nucleon to Delta transition form factor.
We study light meson properties in a magnetic field, focusing on a charged pion and a charged and polarized rho meson, in quenched lattice QCD. The gauge-invariant density-density correlators are calculated to investigate the deformation caused by the magnetic field. We find that these mesons acquire elongated shapes along the magnetic field. The magnitude of the deformation is about 10-20 % when the strength of the magnetic field is of the order of the squared unphysical pion mass.
Proposals for physics beyond the standard model often include new colored particles at or beyond the scale of electroweak symmetry breaking. Any new particle with a sufficient lifetime will bind with standard model gluons and quarks to form a spectrum of new hadrons. Here we focus on colored particles in the octet, decuplet, 27-plet, 28-plet and 35-plet representations of SU(3) color because these can form hadrons without valence quarks. In every case, lattice creation operators are constructed for all angular momentum, parity and charge conjugation quantum numbers. Computations with fully-dynamical lattice QCD configurations produce numerical results for mass splittings within this new hadron spectrum. A previous quenched lattice study explored the octet case for certain quantum number choices, and our findings provide a reassessment of those early results.
Systems with the quantum numbers of up to twelve charged and neutral pseudoscalar mesons, as well as one-, two-, and three-nucleon systems, are studied using dynamical lattice quantum chromodynamics and quantum electrodynamics (QCD+QED) calculations and effective field theory. QED effects on hadronic interactions are determined by comparing systems of charged and neutral hadrons after tuning the quark masses to remove strong isospin breaking effects. A non-relativistic effective field theory, which perturbatively includes finite-volume Coulomb effects, is analyzed for systems of multiple charged hadrons and found to accurately reproduce the lattice QCD+QED results. QED effects on charged multi-hadron systems beyond Coulomb photon exchange are determined by comparing the two- and three-body interaction parameters extracted from the lattice QCD+QED results for charged and neutral multi-hadron systems.
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