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A More improved lattice action for heavy quarks

Description: We extend the Fermilab formalism for heavy quarks to develop a more improved action. We give results of matching calculations of the improvement couplings at tree level. Finally, we estimate the discretization errors associated with the new action.
Date: March 17, 2004
Creator: al., M. B. Oktay et
Partner: UNT Libraries Government Documents Department

Taste changing in staggered quarks

Description: The authors present results from a systematic perturbative investigation of taste-changing in improved staggered quarks. They show one-loop taste-changing interactions can be removed perturbatively by an effective four-quark term and calculate the necessary coefficients.
Date: January 5, 2004
Creator: al., Quentin Mason et
Partner: UNT Libraries Government Documents Department


Description: Cooling lattices consisting only of bends (using either rotated pole faces or gradient dipoles to achieve focusing) often require large apertures and short magnets. One expects the effect of end fields to be significant in this case. In this paper we explore the effect of adding end fields to a working lattice design that originally lacked them. The paper describes the process of correcting the lattice design for the added end fields so as to maintain desirable lattice characteristics. It then compares the properties of the lattice with end fields relative to the lattice without them.
Date: June 26, 2003
Partner: UNT Libraries Government Documents Department

A lattice formulation of chiral gauge theories

Description: We present a method for implementing gauge theories of chiral fermions on the lattice. Discussed topics include: the lattice as a UV regulator, a chiral QED model, modification of the fermion determinant, large gauge-field momenta, and a non-perturbative problem.
Date: August 1, 1996
Creator: Bodwin, G.T.
Partner: UNT Libraries Government Documents Department

Static hybrid quarkonium potential with improved staggered quarks

Description: The authors are studying the effects of light dynamical quarks on the excitation energies of a flux tube between a static quark and antiquark. They report preliminary results of an analysis of the ground state potential and the {Sigma}{prime}{sub g}{sup +} and II{sub u} potentials. They have measured these potentials on closely matched ensembles of gauge configurations, generated in the quenched approximation and with 2+1 flavors of Asqtad improved staggered quarks.
Date: January 6, 2004
Creator: al., C. Bernard et
Partner: UNT Libraries Government Documents Department

The second moment of the pion light cone wave function

Description: We present a preliminary result for second moment of the light cone wave function of the pion. This parameter is the subject of a discrepancy between theoretical predictions (coming from lattice and sum rules) and a recent experimental result (that remarkably agrees with purely perturbative predictions). In this work we exploit lattice hypercubic symmetries to remove power divergences and, moreover, implement a full 1-loop matching for all the contributing operators.
Date: September 25, 2003
Creator: Debbio, Luigi del; Pierro, Massimo di & Dougall, Alex
Partner: UNT Libraries Government Documents Department

A relativistic O (a{sup 2}) improved action for heavy quarks

Description: The authors extend the Fermilab formalism for heavy quarks to develop an {Omicron}(a{sup 2}) improved relativistic action. They discuss their construction of the action, including the identification of redundant operators and the calculation of the improvement coefficients.
Date: January 5, 2004
Creator: al., M. B. Oktay et
Partner: UNT Libraries Government Documents Department

Recent results using all point quark propagators

Description: Pseudofermion methods for extracting all-point quark propagators are reviewed, with special emphasis on techniques for reducing or eliminating autocorrelations induced by low eigenmodes of the quark Dirac operator. Recent applications, including high statistics evaluations of hadronic current correlators and the pion form factor, are also described.
Date: January 6, 2004
Creator: Duncan, A. & Yoo, E. Eichten and J.
Partner: UNT Libraries Government Documents Department

QCD with chiral 4-fermion interactions ({chi}QCD)

Description: Lattice QCD with staggered quarks is augmented by the addition of a chiral 4-fermion interaction. The Dirac operator is now non-singular at m{sub q}=0, decreasing the computing requirements for light quark simulations by at least an order of magnitude. We present preliminary results from simulations at finite and zero temperatures for m{sub q}=0, with and without gauge fields. Chiral QCD enables simulations at physical u and d quark masses with at least an order of magnitude saving in CPU time. It also enables simulations with zero quark masses which is important for determining the equation of state. A renormalization group analysis will be needed to continue to the continuum limit. 7 refs., 2 figs.
Date: October 1, 1996
Creator: Kogut, J.B. & Sinclair, D.K.
Partner: UNT Libraries Government Documents Department

Bbar {right arrow} {pi}l {nu bar}}at three lattice spacings

Description: The increasing accuracy of experimental results for the exclusive, semileptonic decay {anti B}{yields}{pi}l{anti {nu}} requires a similarly acucrate calculation of the hadronic matrix elements, to determine {vert_bar}V{sub ub}{vert_bar}. We present preliminary results for the form factors of the B to light meson decay mode. Using results from three lattices in the range 5.7{<=}{beta}{<=}6.1 we study the dependence on the lattice spacing.
Date: November 1, 1998
Creator: S. Ryan, A. El-Khadra, S. Hashimoto, A. Kronfeld, P. Mackenzie, and J. Simone
Partner: UNT Libraries Government Documents Department

Physics of the 1 Teraflop RIKEN-BNL-Columbia QCD project. Proceedings of RIKEN BNL Research Center workshop: Volume 13

Description: A workshop was held at the RIKEN-BNL Research Center on October 16, 1998, as part of the first anniversary celebration for the center. This meeting brought together the physicists from RIKEN-BNL, BNL and Columbia who are using the QCDSP (Quantum Chromodynamics on Digital Signal Processors) computer at the RIKEN-BNL Research Center for studies of QCD. Many of the talks in the workshop were devoted to domain wall fermions, a discretization of the continuum description of fermions which preserves the global symmetries of the continuum, even at finite lattice spacing. This formulation has been the subject of analytic investigation for some time and has reached the stage where large-scale simulations in QCD seem very promising. With the computational power available from the QCDSP computers, scientists are looking forward to an exciting time for numerical simulations of QCD.
Date: October 16, 1998
Partner: UNT Libraries Government Documents Department

Spectroscopy of B{sub s} and D{sub s} mesons

Description: We study B{sub s} and D{sub s} spectroscopy in quenched lattice QCD using the Fermilab approach to heavy quarks. We obtain results at four lattice spacings, a, using O(a)-improved Wilson quarks. We compare and contrast the various methods for heavy quarks on the lattice, discussing which methods work best for different physical systems and the ease with which calculations may be performed.
Date: January 1, 1998
Creator: MacKenzie, P.B.; Ryan, S.M. & Simone, J.N.
Partner: UNT Libraries Government Documents Department

Single identities for lattice theory and for weakly associative lattices

Description: We present a single identity for the variety of all lattices that is much simpler than those previously known to us. We also show that the variety of weakly associative lattices is one-based, and we present a generalized one-based theorem for subvarieties of weakly associative lattices that can be defined with absorption laws. The automated theorem-proving program OTTER was used in substantial way to obtain the results.
Date: March 13, 1995
Creator: McCune, W. & Padmanabhan, R.
Partner: UNT Libraries Government Documents Department

Introduction to lattice QCD

Description: The goal of the lectures on lattice QCD (LQCD) is to provide an overview of both the technical issues and the progress made so far in obtaining phenomenologically useful numbers. The lectures consist of three parts. The author`s charter is to provide an introduction to LQCD and outline the scope of LQCD calculations. In the second set of lectures, Guido Martinelli will discuss the progress they have made so far in obtaining results, and their impact on Standard Model phenomenology. Finally, Martin Luescher will discuss the topical subjects of chiral symmetry, improved formulation of lattice QCD, and the impact these improvements will have on the quality of results expected from the next generation of simulations.
Date: December 1998
Creator: Gupta, R.
Partner: UNT Libraries Government Documents Department

A lattice formulation of chiral gauge theories

Description: The authors present a method for formulating gauge theories of chiral fermions in lattice field theory. The method makes use of a Wilson mass to remove doublers. Gauge invariance is then restored by modifying the theory in two ways: the magnitude of the fermion determinant is replaced with the square root of the determinant for a fermion with vector-like couplings to the gauge field; a double limit is taken in which the lattice spacing associated with the fermion field is taken to zero before the lattice spacing associated with the gauge field. The method applies only to theories whose fermions are in an anomaly-free representation of the gauge group. They also present a related technique for computing matrix elements of operators involving fermion fields. Although the analyses of these methods are couched in weak-coupling perturbation theory, it is argued that computational prescriptions are gauge invariant in the presence of a nonperturbative gauge-field configuration.
Date: December 1, 1995
Creator: Bodwin, G.T.
Partner: UNT Libraries Government Documents Department

Improving the staggered quark action to reduce flavor symmetry violations

Description: The authors investigate a class of actions for lattice QCD with staggered quarks aimed at reducing the flavor symmetry violations associated with using staggered fermions. These actions replace the gauge field link fields in the quark action with covariantly smeared fields. As such they are an extension of actions considered by the MILC collaboration. They show that such actions systematically reduce flavor symmetry violations in the weak coupling limit. Using the mass splitting between Goldstone and non-Goldstone pions as a measure of flavor symmetry violations they find that these actions have considerably less flavor symmetry violations than the standard staggered action, and represent an improvement on what can be achieved with the MILC action, on quenched configurations with {beta} = 5.7.
Date: July 1, 1998
Creator: Lagaee, J.F. & Sinclair, D.K.
Partner: UNT Libraries Government Documents Department

O(1/M{sup 3}) effects for heavy-light mesons in lattice NRQCD

Description: The masses of spin-singlet and spin-triplet S-wave mesons containing a single heavy quark are computed in the quenched approximation. The light quark action and gauge field action are both classically-improved and tadpole-improved, and the couplings to the heavy quark are organized by the 1/M expansion of tadpole-improved NRQCD. At each of two lattice spacings, near 0.22fm and 0.26fm, meson masses are obtained for heavy quarks spanning the region between charmed and bottom mesons. Results up to O(1/M), O(1/M{sup 2})and O(1/M{sup 3}) are displayed separately, so that the convergence of the heavy quark expansion can be discussed. Also, the effect of each term in the O(1/M{sup 3}) contribution is computed individually. For bottom mesons the 1/M-expansion appears to be satisfactory, but the situation for charmed mesons is less clear.
Date: March 1998
Creator: Lewis, Randy & Woloshyn, R. M.
Partner: UNT Libraries Government Documents Department

High temperature meson propagators with domain-wall quarks.

Description: We study the chiral properties of domain-wall quarks at high temperatures on an ensemble of quenched configurations. Low lying eigenmodes of the Dirac operator are calculated and used to check the extent to which the Atiyah-Singer index theorem is obeyed on lattices with finite N{sub 5}. We calculate the connected and disconnected screening propagators for the lowest mass scalar and pseudoscalar mesons in the sectors of different topological charge and note that they behave as expected. Separating out the would-be zero eigenmodes enables us to accurately estimate the disconnected propagators with far less effort than would be needed otherwise.
Date: September 23, 1999
Creator: Lagae, J.-F. & Sinclair, D. K.
Partner: UNT Libraries Government Documents Department

Topology, fermionic zero modes and flavor singlet correlators in finite temperature QCD

Description: Among the non-perturbative properties of quarks, those associated with the topology of the gauge fields occupy a special place. This follows from the Atiyah-Singer index theorem which guarantees the existence of fermionic zero modes on configurations with non-trivial topology. As a result, non-perturbative issues related to the axial anomaly can generally be studied with enhanced control. In the context of finite temperature QCD, one such issue relates to the realization of the anomalous U(1) axial symmetry. If this symmetry were to be effectively restored at the critical temperature, the increased number of soft degrees of freedom would modify the nature of the phase transition. Needless to say, only the lattice can really hope to tackle this question, at this time. Unfortunately, the lattice formulation also introduces artifacts and there is for example no exact index theorem in this context. Instead, what is observed with the actions currently used is the zero mode shift phenomenon (i.e. modes with small but non-zero eigenvalue and which are not exactly chiral). What the authors would like to show here is that even in this case, enough is recognizable of the continuum behavior that meaningful conclusions can be drawn. They find that the U{sub A}(1) symmetry is not restored at the phase transition but only at somewhat higher temperatures. At the same time, it is clear that detailed quantitative questions could only be answered with the use of an improved action.
Date: October 1, 1997
Creator: Kogut, J.B.; Lagaee, J.F. & Sinclair, D.K.
Partner: UNT Libraries Government Documents Department

N* Spectrum using an O(a)-Improved Fermion Action

Description: The construction of operators and calculational methods for the determination of the N* spectrum are discussed. The masses of the parity partners of the nucleon and delta are computed from the O(a)-improved data of the UKQCD Collaboration, and a clear splitting observed between the mass of the nucleon and its parity partner.
Date: August 1, 2000
Creator: Collaboration, LHPC; Collaboration, UKQCD & Richards, D.G.
Partner: UNT Libraries Government Documents Department