Studies In Hadron Structure Using Lattice Qcd With Quark Masses That Almost Reach The Physical Point

Author : David Richards
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (316 download)

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Download or read book Hadron Structure Using DWF Quarks on an Asqtad Sea written by David Richards and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Moments of unpolarized, helicity, and transversity distributions, electromagnetic form factors, and generalized form factors of the nucleon are presented from a preliminary analysis of lattice results using pion masses down to 359 MeV[1]. We employ a hybrid approach, in which improved, staggered quarks are used for the generation of the gauge configurations, whilst domain-wall fermions, with their desirable chiral properties, are used for the valence quarks. The nucleon axial-vector charge, a benchmark quantity of QCD, is particularly robust under chiral extrapolation; the consistency of the hybrid calculation, both with other lattice calculations, and with experiment at the physical pion mass, is encouraging[2]. Lattice moments of structure functions and GPDs likewise require extrapolation to the physical quark masses; a long-standing puzzle has been the flat behavior of the flavour-non-singlet momentum fraction, x, of the nucleon, at a value considerably higher than the experimental value. An approach in which we apply {chi}PT, with low-energy constants g{sub A} and f{sub {pi}} given by their lattice values at each quark mass, allows a two-parameter extrapolation in m{sub {pi}}{sup lat}/f{sub {pi}}{sup lat} to yield a value for x, and other benchmark quantities, at the physical quark masses that are consistent with experiment. This development encourages to now exploit the predictive power of these calculations. The low-Q{sup 2} behavior of the nucleon form factors describes the distribution of charge and magnetism within a nucleon. The slope of the F{sub 1} form factor is related to the rms charge radius; the chiral extrapolation of the isovector charge radius likewise yields values consistent with experiment[3]. Generalized Parton Distributions provide new insight to hadron structure. For example, the total angular momentum carried by the quarks is related to a combination of moments J{sub q} = 1/2(A{sub 20}{sup u+d} + B{sub 20}{sup u+d})[4]. Combined with measurements of quark spins, we find the total orbital angular momentum carried by quarks is small, though that carried by individual flavours is substantial.