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The overlap-Dirac operator: Topology and chiral symmetry breaking

Description: The authors review the spectral flow techniques for computing the index of the overlap Dirac operator including results relevant for SUSY Yang-Mills theories. They describe properties of the overlap Dirac operator, and methods to implement it numerically. They use the results from the spectral flow to illuminate the difficulties in numerical calculations involving domain wall and overlap fermions.
Date: January 1, 2000
Creator: Edwards, R.G.; Heller, U.M. & Narayanan, R.
Partner: UNT Libraries Government Documents Department

[Support of theoretical high energy physics research at the Supercomputer Computations Research Institute]. Final report, September 30, 1992--July 31, 1997

Description: The research primarily involved lattice field theory simulations such as Quantum Chromodynamics (QCD) and the Standard Model of electroweak interactions. Among the works completed by the members of the lattice group and their outside collaborators in QCD simulations are extensive hadronic spectrum computations with both Wilson and staggered fermions, and calculations of hadronic matrix elements and wavefunctions. Studies of the QCD {beta} function with two flavors of Wilson fermions, and the study of a possible flavor-parity breaking phase in QCD with two flavors of Wilson fermions have been completed. Studies of the finite temperature behavior of QCD have also been a major activity within the group. Studies of non-relativistic QCD, both for heavy-heavy mesons and for the heavy quark in heavy-light mesons have been done. Combining large N analytic computations within the Higgs sector of the standard model and numerical simulations at N = 4 have yielded a computation of the upper bound of the mass of the Higgs particle, as well as the energy scale above which deviations from the Standard Model may be expected. A major research topic during the second half of the grant period was the study of improved lattice actions, designed to diminish finite lattice spacing effects and thus accelerate the approach to the continuum limit. A new exact Local Hybrid Monte Carlo (overrelaxation) algorithm with a tunable overrelaxation parameter has been developed for pure gauge theories. The characteristics of this algorithm have been investigated. A study of possible instabilities in the global HMC algorithm has been completed.
Date: December 15, 1998
Creator: Bitar, K.M.; Edwards, R.G.; Heller, U.M. & Kennedy, A.D.
Partner: UNT Libraries Government Documents Department

Chiral condensate in the deconfined phase of quenched gauge theories

Description: The authors compute the low lying spectrum of the overlap Dirac operator in the deconfined phase of finite-temperature quenched gauge theory. It suggests the existence of a chiral condensate which they confirm with a direct stochastic estimate. They show that the part of the spectrum responsible for the chiral condensate can be understood as arising from a dilute gas of instantons and anti-instantons.
Date: October 25, 1999
Creator: Edwards, R.G..; Heller, U.M..; Kiskis, J. & Narayanan, R.
Partner: UNT Libraries Government Documents Department

The decay constants f(B) and f(D+) from three-flavor lattice QCD

Description: We present new preliminary results for the leptonic decay constants f{sub B} and f{sub D+} determined in 2+1 flavor lattice QCD at lattice spacings a = 0.09, 0.12 and 0.15 fm. Results are obtained using the MILC Collaboration gauge configuration ensembles, clover heavy quarks in the Fermilab interpretation and improved staggered light quarks. Decay constants, computed at partially quenched combinations of the valence and sea light quark masses, are used to determine the low-energy parameters of staggered chiral perturbation theory. The physical decay constants are found in an extrapolation using the parameterized chiral formula.
Date: January 1, 2007
Creator: Bernard, C.; DeTar, C.; Di Pierro, M.; El-Khadra, A. X.; Evans, R. T.; Freeland, E. et al.
Partner: UNT Libraries Government Documents Department

B and D Meson Decay Constants

Description: We present an update of our calculations of the decay constants of the D, D{sub s}, B, and B{sub s} mesons in unquenched 2+1 flavor QCD. We use the MILC library of improved staggered gauge ensembles at lattice spacings 0.09, 0.12, and 0.15 fm, clover heavy quarks with the Fermilab normalizations, and improved staggered light valence quarks.
Date: April 1, 2009
Creator: Bernard, C.; DeTar, C.; Di Pierro, M.; El-Khadra, A. X.; Evans, R. T.; Freeland, Elizabeth Dawn et al.
Partner: UNT Libraries Government Documents Department

Visualization of semileptonic form factors from lattice QCD

Description: Comparisons of lattice-QCD calculations of semileptonic form factors with experimental measurements often display two sets of points, one each for lattice QCD and experiment. Here we propose to display the output of a lattice-QCD analysis as a curve and error band. This is justified, because lattice-QCD results rely in part on fitting, both for the chiral extrapolation and to extend lattice-QCD data over the full physically allowed kinematic domain. To display an error band, correlations in the fit parameters must be taken into account. For the statistical error, the correlation comes from the fit. To illustrate how to address correlations in the systematic errors, we use the Becirevic-Kaidalov parametrization of the D {yields} {pi}{ell}{nu} and D {yields} K{ell}{nu} form factors, and a analyticity-based fit for the B {yields} {pi}{ell}{nu} form factor f{sub +}.
Date: June 1, 2009
Creator: Bernard, C.; DeTar, C.; Di Pierro, M.; El-Khadra, A. X.; Evans, R. T.; Freeland, E. D. et al.
Partner: UNT Libraries Government Documents Department

The Ds and D+ Leptonic Decay Constants from Lattice QCD

Description: We present the leptonic decay constants f{sub D{sub s}} and f{sub D{sup +}} computed on the MILC collaboration's 2+1 flavor asqtad gauge ensembles. We use clover heavy quarks with the Fermilab interpretation and improved staggered light quarks. The simultaneous chiral and continuum extrapolation, which determines both decay constants, includes partially-quenched lattice results at lattice spacings a {approx} 0.09, 0.12 and 0.15 fm. We have made several recent improvements in our analysis: (a) we include terms in the fit describing leading order heavy-quark discretization effects, (b) we have adopted a more precise input r{sub 1} value consistent with our other D and B meson studies, (c) we have retuned the input bare charm masses based upon the new r{sub 1}. Our preliminary results are f{sub D{sub s}} = 260 {+-} 10 MeV and f{sub D{sup +}} = 217 {+-} 10 MeV.
Date: December 1, 2009
Creator: Bazavov, A.; Bernard, C.; DeTar, C.; Freeland, E. D.; Gamiz, E.; Gottlieb, Steven et al.
Partner: UNT Libraries Government Documents Department

B -> D* l nu at zero recoil: an update

Description: We present an update of our calculation of the form factor for {bar B} {yields} D*{ell}{bar {nu}} at zero recoil, with higher statistics and finer lattices. As before, we use the Fermilab action for b and c quarks, the asqtad staggered action for light valence quarks, and the MILC ensembles for gluons and light quarks (Luescher-Weisz married to 2+1 rooted staggered sea quarks). In this update, we have reduced the total uncertainty on F(1) from 2.6% to 1.7%.
Date: November 1, 2010
Creator: Bailey, Jon A.; Bazavov, A.; Bernard, C.; Bouchard, C.M.; DeTar, C.; El-Khadra, A.X. et al.
Partner: UNT Libraries Government Documents Department

Semileptonic decays of K and D mesons in 2+1 flavor QCD

Description: The experimentally measured rates of the semileptonic decays K {yields} {pi}/{nu} and D {yields} K({pi})/{nu} can be combined with lattice calculations of the associated form factors to precisely extract the CKM matrix elements |V{sub us}| and |V{sub cs(d)}|. We report on the status of form factor calculations with Fermilab charm quarks and staggered light quarks on the 2+1 flavor asqtad staggered MILC ensembles. Analysis of data for the D {yields} {pi}/{nu} form factor provides a nontrivial test of our methods via comparison with CLEO data. We discuss the use of HISQ valence quarks to calculate the K {yields} {pi}/{nu} form factor f{sub +}{sup K{pi}}(0) and describe tests of our method.
Date: November 1, 2010
Creator: Bailey, Jon A.; Bazavov, A.; Bernard, C.; Bouchard, C.M.; DeTar, C.; El-Khadra, A.X. et al.
Partner: UNT Libraries Government Documents Department

Moments of Nucleon Light Cone Quark Distributions Calculated in Full Lattice QCD

Description: Moments of the quark density, helicity, and transversity distributions are calculated in unquenched lattice QCD. Calculations of proton matrix elements of operators corresponding to these moments through the operator product expansion have been performed on the 16{sup 3} x 32 lattices for Wilson fermions at Beta=5.6 using configurations from the SESAM collaboration and at Beta = 5.5 using configurations from SCRI. One-loop perturbative renormalization corrections are included. At quark masses accessible in present calculations, there is no statistically significant difference between quenched and full QCD results, indicating that the contributions of quark-antiquark excitations from the Dirac Sea are small. Close agreement between calculations with cooled configurations containing essentially only instantons and the full gluon configurations indicates that quark zero modes associated with instantons play a dominant role. Naive linear extrapolation of the full QCD calculation to the physical pion mass yields results inconsistent with experiment. Extrapolation to the chiral limit including the physics of the pion cloud can resolve this discrepancy and the requirements for a definitive chiral extrapolation are described.
Date: January 1, 2002
Creator: Dolgov, D.; Brower, R.; Capitani, S.; Dreher, P.; Negele, J.W.; Pochinsky, A. et al.
Partner: UNT Libraries Government Documents Department

Moments of Structure Functions in Full QCD

Description: Moments of the quark density distribution, moments of the quark helicity distribution, and the tensor charge are calculated in full QCD. Calculations of matrix elements of operators from the operator product expansion have been performed on 16{sup 3} x 32 lattices for Wilson fermions at {beta} = 5.6 using configurations from the SESAM collaboration and at {beta} = 5.5 using configurations from SCRI. One-loop perturbative renormalization corrections are included. Selected results are compared with corresponding quenched calculations and with calculations using cooled configurations.
Date: August 1, 2000
Creator: Dolgov, D.; Brower, R.; Capitani, S.; Negele, J. W.; Pochinsky, A.; Renner, D. et al.
Partner: UNT Libraries Government Documents Department

Continuum Extrapolation of Moments Nucleon Quark Distributions in Full QCD

Description: Moments of light cone quark density, helicity, and transversity distributions are calculated in unquenched lattice QCD at {beta} = 5.5 and {beta} = 5.3 using Wilson fermions on 16{sup 3} x 32 lattices. These results are combined with earlier calculations at {beta} = 5.6 using SESAM configurations to study the continuum limit.
Date: June 1, 2002
Creator: Dreher, P.; Brower, R.; Capitani, S.; Dolgov, D.; Edwards, R.; Eicker, N. et al.
Partner: UNT Libraries Government Documents Department

Charmed meson decay constants in three-flavor lattice QCD

Description: The authors present the first lattice QCD calculation with realistic sea quark content of the D{sup +}-meson decay constant f{sub D+}. They use the MILC Collaboration's publicly available ensembles of lattice gauge fields, which have a quark sea with two flavors (up and down) much lighter than a third (strange). They obtain f{sub D+} = 201 {+-} 3 {+-} 17 MeV, where the errors are statistical and a combination of systematic errors. They also obtain f{sub D{sub s}} = 249 {+-} 3 {+-} 16 MeV for the D{sub s} meson.
Date: June 1, 2005
Creator: Aubin, C.; Bernard, C.; DeTar, C.; Di Pierro, M.; Freeland, Elizabeth D.; Gottlieb, Steven et al.
Partner: UNT Libraries Government Documents Department

Glueballs and topological charge in the presence of dynamical quarks

Description: We have estimated the string tension and the masses of the 0{sup ++} and 2{sup ++} glueballs in lattice QCD with 2 light flavours of staggered quarks. In addition we have measured the topological charge and hence susceptibility of our gauge field configurations. The simulations were performed at 6/g{sup 2}=5.6 and quark masses m=0.01 and 0.025 (lattice units) on lattice sizes ranging from 12{sup 4} to 16{sup 4}. 7 refs., 5 figs.
Date: November 1, 1990
Creator: Bitar, K.M.; Edwards, R.; Heller, U.M.; Kennedy, A.D. (Florida State Univ., Tallahassee, FL (USA). Supercomputer Computations Research Inst.); DeGrand, T.A. (Colorado Univ., Boulder, CO (USA). Dept. of Physics); Gottlieb, S. et al.
Partner: UNT Libraries Government Documents Department

Thermodynamics of lattice QCD with 2 light dynamical (staggered) quark flavours on a 16 sup 3 times 8 lattice

Description: Lattice QCD with 2 light staggered quark flavours is being simulated on a 16{sup 3} {times} 8 lattice to study the transition from hadronic matter to a quark gluon plasma. We have completed runs at m{sub q} = 0.0125 and are extending this to m{sub q} = 0.00625. We also examine the addition of a non-dynamical strange'' quark. Thermodynamic order parameters are being measured across the transition and further into the plasma phase, as are various screening lengths. No evidence for a first order transition is seen, and we estimate the transition temperature to be {Tc} = 143(7)MeV.
Date: January 1, 1991
Creator: Gottlieb, S.; Krasnitz, A. (Indiana Univ., Bloomington, IN (United States). Dept. of Physics); Heller, U.M.; Kennedy, A.D. (Florida State Univ., Tallahassee, FL (United States). Supercomputer Computations Research Inst.); Kogut, J.B. (Illinois Univ., Urbana, IL (United States). Dept. of Physics); Liu, W. (Thinking Machines Corp., Cambridge, MA (United States)) et al.
Partner: UNT Libraries Government Documents Department