Review of Hadron Structure Calculations on a Lattice

I present a review of the current status and the most recent achievements in lattice QCD calculations of hadron structure. First, I overview the status and systematic uncertainties of nucleon structure "benchmark" quantities that are well known from experiments and serve as a reference point for the validity of lattice QCD methods. Next, I discuss the current status of calculations of form factors of the nucleon and highlight some recent results for other hadrons that are important for understanding their internal dynamics. Wave functions of hadrons and their excitations may also be studied in lattice QCD, and I illustrate it with two recent examples of such calculations. Finally, I discuss in detail the state of calculations pertaining to the nucleon spin puzzle.Comment: 14 pages, 15 figures. Plenary talk at the XXXI International Symposium on Lattice Field Theory, Lattice2013, July 29-August 3, 2013, Mainz, German

Entanglement Entropy due to the Presence of Static Quarks

We study the entanglement of gluon fields in presence of a static $Q\bar Q$ pair in quenched QCD. Using the replica method, we investigate the $q=2$ Renyi entropy of the entanglement of gluon fields inside and in the vicinity of the confining QCD string between the quark and the antiquark. We find that there is excess entropy of gluon entanglement compared to vacuum fluctuations. This excess of entanglement entropy is associated with the gluon flux tube, and we find that it has a finite non-zero value in the continuum. We investigate the dependence of gluon entanglement on the geometry of longitudinal and transverse partitioning of the flux tube. Our preliminary results suggest scaling of the entanglement entropy with the area of the boundary overlapping with the flux tube.Comment: 7 pages, 6 figures, Proceedings of the 40th International Symposium on Lattice Field Theory (Lattice 2023), July 31st - August 4th, 2023, Fermilab, Batavia, Illinois, US

Exploration of nucleon structure in lattice QCD with chiral quarks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 185-195).In this work, we calculate various nucleon structure observables using the fundamental theory of quarks and gluons, QCD, simulated on a lattice. In our simulations, we use the full QCD action including Nf = 2+ 1 dynamical quarks in the SU(2) isospin limit. We compute the nucleon vector and axial vector form factors as well as the generalized form factors, and analyze the nucleon charge, magnetization, and axial radii, anomalous magnetic moment, and axial charge. In addition, we compute quark contributions to the nucleon momentum and spin. Our calculation is novel for three reasons. It is a first full QCD calculation using both sea and valence chiral quarks with pion masses as low as m[pi] = 300 MeV. We develop a method to keep systematic effects in the lattice nucleon matrix elements under control, which helps us to obtain a better signal-to-noise ratio, to achieve higher precision and to test the applicability of low-energy effective theories. Finally, we compare the results from lattice QCD calculations with two different discretization methods and lattice spacings, with the rest of the calculation technique kept equal. The level of agreement between these results indicates that our calculations are not significantly affected by discretization effects.by Sergey Nikolaevich Syritsyn.Ph.D

Nucleon structure with pion mass down to 149 MeV

We present isovector nucleon observables: the axial, tensor, and scalar charges and the Dirac radius. Using the BMW clover-improved Wilson action and pion masses as low as 149 MeV, we achieve good control over chiral extrapolation to the physical point. Our analysis is done using three different source-sink separations in order to identify excited-state effects, and we make use of the summation method to reduce their size.Comment: 7 pages, 5 figures. Talk presented at the 30th International Symposium on Lattice Field Theory (Lattice 2012), June 24-29, 2012, Cairns, Australi

Nucleon form factors with light Wilson quarks

We present nucleon observables - primarily isovector vector form factors - from calculations using 2+1 flavors of Wilson quarks. One ensemble is used for a dedicated high-precision study of excited-state effects using five source-sink separations between 0.7 and 1.6 fm. We also present results from a larger set of calculations that include an ensemble with pion mass 149 MeV and box size 5.6 fm, which nearly eliminates the uncertainty associated with extrapolation to the physical pion mass. The results show agreement with experiment for the vector form factors, which occurs only when excited-state contributions are reduced. Finally, we show results from a subset of ensembles that have pion mass 254 MeV with varying temporal and spatial box sizes, which we use for a controlled study of finite-volume effects and a test of the "$m_\pi L=4$" rule of thumb.Comment: 7 pages, 3 figures. Talk presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), July 29-August 3, 2013, Mainz, German