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Hadron Structure from Lattice QCD

Project HSQCD
Research Area Plasma & Particle Physics
Principal Investigator(s) Prof. Constantia Alexandrou
  • University of Cyprus, Department of Physics, Nicosia, Cyprus
  • The Cyprus Institute, Nicosia, Cyprus
  • National Technical University of Athens / Hellenic Naval Academy, Athens, Greece
  • Forschungszentrum J├╝lich, Germany


We utilize Lattice QCD, the only non-perturbative scheme which allows for the exploration of Hadron Structure starting from the fundamental Lagrangian of the theory. Simulating QCD is a challenging and demanding computational task, ideally suited for high-capacity HPC platforms such as those provided by DEISA. The primary computational cost of Lattice QCD calculations outlined in this proposal is the inversion of the large, sparse Dirac matrix, which is a function of the quark mass. Generally Lattice QCD calculations are performed at heavier masses than at the physical quark masses. Computational cost and physical accuracy greatly increase with decreased quark mass (as measured by the mass of the resulting pions).
Utilization of DEISA computing resources becomes crucial, especially when the simulations involve the use of fine dynamical Domain Wall Fermion (DWF) lattices (32^3 x 64 x16) at pion mass as low as 297 MeV. DWF is a discretization scheme which improves the chiral properties of the fermions at increased computational cost (5-dimensional lattice instead of four).
In particular, this project makes use of the resources provided by DEISA in order to employ lattice QCD techniques and perform hadron matrix calculations, which explore the electromagnetic and weak transition form factors for the Nucleon-to-Delta process, the Delta electromagnetic and axial form factors and the Omega baryon electromagnetic form factors. Computation of the highly sensitive suppressed form factors is expected to shed light on the deformation of baryons.
The extraction of the quadrupole form factors in Nucleon-to-Delta transition and as well as in the Delta-Delta connected to deformation requires very high statistics making the problem computationally demanding. To improve the accuracy for the calculation of subdominant form factors we employ the coherent-sink technique which quadruples the statistics per sequential inversion.
Finally the study involves also an exploratory computation where the gauge noise dominated disconnected three-point functions are taken into account. The inclusion of such quantities is important, for instance in the case of the Delta and Omega electromagnetic form factors as well as in studies of decays of unstable particles such as the Delta. To explore methods for the computation of isoscalar form factors, keeping the computational cost as low as possible, the measurements of such quantities, which involve the computation of all-to-all propagators, are performed using two dynamical flavors of Wilson fermions on 32^3x 64.

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