The nucleon to Delta electromagnetic transition form factors in lattice QCD

The electromagnetic nucleon to Delta transition form factors are evaluated using two degenerate flavors of dynamical Wilson fermions and using dynamical sea staggered fermions with domain wall valence quarks. The two subdominant quadrupole form factors are evaluated for the first time in full QCD to sufficient accuracy to exclude a zero value, which is taken as a signal for deformation in the nucleon-Delta system. For the Coulomb quadrupole form factor the unquenched results show deviations from the quenched results at low q^2 bringing dynamical lattice results closer to experiment, thereby confirming the importance of pion cloud contributions on this quantity.Comment: 15 pages, 8 Figure

Hadron wave functions and the issue of nucleon deformation

Using gauge invariant hadronic two- and three- density correlators we extract information on the spatial distributions of quarks in hadrons, and on hadron shape and multipole moments within quenched lattice QCD. Combined with the calculation of N to Delta transition amplitudes the issue of nucleon deformation can be addressed.Comment: 4 pages, 7 figures. Talk presented at the PANIC02 conference, Sept. 30 - Oct. 4, 2002, Osaka, Japan. Discussion of the N to Delta results modifie

Hadron Deformation and Form Factors from Lattice QCD

We review the current status of lattice QCD studies of the nucleon system. In particular, we focus on the determination of the shape of the nucleon by probing its wave function as well as by evaluating the N to Delta transition form factors.Comment: 14 pages, 8 figures. Talk presented at the Workshop "The Shape of Hadrons", Athens, Greece, 27-30 April 200

N to Delta electromagnetic and axial form factors in full QCD

Lattice results on the N to Delta electromagnetic, axial-vector and pseudoscalar form factors are evaluated using dynamical staggered sea quarks and domain wall valence quarks for pion masses in the range of 580-350 MeV, as well as, dynamical and quenched Wilson fermions for similar pion masses.Comment: 8 pages, 6 Figures. Invited talk given at the Workshop Exclusive Reactions at High Momentum Transfer, Jefferson Lab, Newport News, USA, May 21-24 200

Hadron deformation from Lattice QCD

We address the issue of hadron deformation within the framework of lattice QCD. For hadrons with spin greater than 1/2 the deformation can be determined by evaluating the charge and matter distributions. Deviation of the nucleon shape from spherical symmetry is determined by evaluating the quadrupole strength in the transition $\gamma N \to \Delta(1232)$ both in the quenched and in the unquenched theory.Comment: 7 pages, Talk given at the second Workshop on Lattice Hadron Physics, Cairns, Australia, 22-30 July 2003. Corrected typo

Axial Nucleon to Delta transition form factors on 2+1 flavor hybrid lattices

We correct the values of the dominant nucleon to Delta axial transition form factors CA_5 and CA_6 published in C. Alexandrou et.al., Phys. Rev. D 76,094511 (2007). The analysis error affects only the values obtained when using the hybrid action in the low Q^2 regime bringing them into agreement with those obtained with Wilson fermions.Comment: 1+2 pages, 2 figures, 1 Table, Erratum to C. Alexandrou et.al., Phys. Rev. D 76, 094511 (2007

Momentum dependence of the N to Delta transition form factors

We present a new method to determine the momentum dependence of the N to Delta transition form factors and demonstrate its effectiveness in the quenched theory at $\beta=6.0$ on a $32^3 \times 64$ lattice. We address a number of technical issues such as the optimal combination of matrix elements and the simultaneous overconstrained analysis of all lattice vector momenta contributing to a given momentum transfer squared, $Q^2$.Comment: Talk presented at Lattice 2004 (spectrum), Fermilab, 21-26 Jun. 2004. 3 pages, 3 figures. One typo in phenomenological Ansatz correcte

Evidence for diquarks in lattice QCD

Diquarks may play an important role in hadron spectroscopy, baryon decays and color superconductivity. We investigate the existence of diquark correlations in lattice QCD by considering systematically all the lowest energy diquark channels in a color gauge-invariant setup. We measure mass differences between the various channels and show that the positive parity scalar diquark is the lightest. Quark-quark correlations inside the diquark are clearly seen in this channel, and yield a diquark size of order 1 fm.Comment: Version as published in Phys. Rev. Lett.97, 222002,2006; 4 pages, 5 figure