Publications (33)30.07 Total impact

Article: Calculation of the neutron electric dipole moment with two dynamical flavors of domain wall fermions
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ABSTRACT: We present a study of the neutron electric dipole moment ($\vec d_N$) within the framework of lattice QCD with two flavors of dynamical lig ht quarks. The dipole moment is sensitive to the topological structure of the gaug e fields, and accuracy can only be achieved by using dynamical, or sea quark, calc ulations. However, the topological charge evolves slowly in these calculations, le ading to a relatively large uncertainty in $\vec d_N$. It is shown, using quenched configurations, that a better sampling of the charge d istribution reduces this problem, but because the CP even part of the fermion determinant is absent, both the topological charge dis tribution and $\vec d_N$ are pathological in the chiral limit. We discuss the statistical and systematic uncertainties arising from the topological charge distr ibution and unphysical size of the quark mass in our calculations and prospects fo r eliminating them. Our calculations employ the RBC collaboration two flavor domain wall fermion and DBW2 gauge action lattices with inverse lattice spacing $a^{1}\approx$ 1.7 GeV, physical volume $V\approx (2$ fm)$^3$, and light quark mass roughly equal to the strange quark mass ($m_{sea}=0.03 $ and 0.04). We determine a value of the electric dipole moment that is zero withi n (statistical) errors, $\vec d_N = 0.04(20)$ e$\theta$fm at the smaller sea quark mass. Satisfactory results for the magnetic and electric form factors of the proton and neutron are also obtained and presented. Comment: 46 pages. Changed one author addressPhysical review D: Particles and fields 12/2005; 
Article: Möbius Fermions
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ABSTRACT: We introduce a new domain wall operator that represents a full (real) Möbius transformation of a given nonchiral Dirac kernel. Shamir's and Chiu/Boriçi's domain wall fermions are special cases of this new class. By tuning the parameters of the Möbius operator and by introducing a new Red/Black preconditioning, we are able to reduce the computational effort substantially.Nuclear Physics B  Proceedings Supplements 11/2005; · 0.88 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We present numerical results for the kaon Bparameter, B_K, determined in the quenched approximation of lattice QCD. Our simulations are performed using domainwall fermions and the renormalization group improved, DBW2 gauge action which combine to give quarks with good chiral symmetry at finite lattice spacing. Operators are renormalized nonperturbatively using the RI/MOM scheme. We study scaling by performing the simulation on two different lattices with a^{1} = 1.982(30) and 2.914(54) GeV. We combine this quenched scaling study with an earlier calculation of B_K using two flavors of dynamical, domainwall quarks at a single lattice spacing to obtain B_K(MS,NDR,mu=2GeV)=0.563(21)(39)(30), were the first error is statistical, the second systematic (without quenching errors) and the third estimates the error due to quenching.Physical review D: Particles and fields 08/2005; 73(9).  [show abstract] [hide abstract]
ABSTRACT: We present preliminary results for nucleon dipole moments computed with domain wall fermions. Our main target is the electric dipole moment of the neutron arising from the theta term in the gauge part of the QCD lagrangian. The calculated magnetic dipole moments of the proton and neutron are in rough accord with experimental values. Comment: 3 pages. Contribution to the proceedings of Lattice 2004 (Fermilab)Nuclear Physics B  Proceedings Supplements 11/2004; · 0.88 Impact Factor 
Article: Scalar meson in dynamical and partially quenched twoflavor QCD: lattice results and chiral loops
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ABSTRACT: This is an exploratory study of the lightest nonsinglet scalar $q\bar q$ state on the lattice with two dynamical quarks. Domain Wall fermions are used for both sea and valence quarks on a 16^3*32 lattice with an inverse lattice spacing of 1.7 GeV. We extract the scalar meson mass 1.58(34) GeV from the exponential timedependence of the dynamical correlators with $m_{val}=m_{sea}$ and N_f=2. Since this statistical errorbar from dynamical correlators is rather large, we analyze also the partially quenched lattice correlators with $m_{val}$ not equal $m_{sea}$. They are positive for $m_{val}>=m_{sea}$ and negative for $m_{val}<m_{sea}$. In order to understand this striking effect of partial quenching, we derive the scalar correlator within the Partially Quenched ChPT and find it describes lattice correlators well. The leading unphysical contribution in Partially Quenched ChPT comes from the exchange of the two pseudoscalar fields and is also positive for $m_{val}>=m_{sea}$ and negative for $m_{val}<m_{sea}$ at large t. After the subtraction of this unphysical contribution from the partially quenched lattice correlators, the correlators are positive and exponentially falling. The resulting scalar meson mass 1.51(19) GeV from the partially quenched correlators is consistent with the dynamical result and has appreciably smaller errorbar.Physical review D: Particles and fields 08/2004; 
Article: Chiral logs with staggered fermions
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ABSTRACT: We compute chiral logarithms in the presence of “taste” symmetry breaking of staggered fermions. The lagrangian of Lee and Sharpe is generalized and then used to calculate the logs in π and K masses. We correct an error in Ref. [1]. MILC data with three light dynamical flavors can be well fit by our formulas. However, two new chiral parameters, which describeO(a2) hairpin diagrams for tastenonsinglet mesons, enter in the fits. To obtain precise results for the physicalO(p4) coefficients, these new parameters will need to be bounded.Nuclear Physics B  Proceedings Supplements 01/2003; · 0.88 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We study theqq¯ singlet and nonsinglet scalarmeson masses using domain wall fermions and the quenched approximation. The singlet mass is found to be smaller than the nonsinglet mass and indicates that the lowest singlet meson state could be lighter than 1 GeV. The twopoint functions for very small quark masses are compared with expectations from the smallvolume chiral perturbation theory and the presence of fermionic zero modes.Nuclear Physics B  Proceedings Supplements. 01/2003;  [show abstract] [hide abstract]
ABSTRACT: We study the chiral properties of quenched domain wall fermions with several gauge actions. We demonstrate that the residual chiral symmetry breaking, which is present for a finite number of lattice sites in the fifth dimension ($L_s$), can be substantially suppressed using improved gauge actions. In particular the Symanzik action, the Iwasaki action, and a renormalization group improved gauge action, called doubly blocked Wilson (DBW2), are studied and compared to the Wilson action. All improved gauge actions studied show a reduction in the additive residual quark mass, $\mres$. Remarkably, in the DBW2 case $\mres$ is roughly two orders of magnitude smaller than the Wilson gauge action at $a^{1}=2$ GeV and $L_s=16$. Significant reduction in $\mres$ is also realized at stronger gauge coupling corresponding to $a^{1}=1.3$ GeV. As our numerical investigation indicates, this reduction is achieved by reducing the number of topological lattice dislocations present in the gauge field configurations. We also present detailed results for the quenched light hadron spectrum and the pion decay constant using the DBW2 gauge action. Comment: 50 pages, 25 figures, RevTeX formated, minor correctionsPhysical Review D 11/2002; · 4.69 Impact Factor 
Article: Chiral Logs With Staggered Fermions
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ABSTRACT: t O(a ). We use the word avor" for dierent staggered elds; lattice avor symmetry is exact for equal masses. MILC's improved staggered (a tad") simulations [3] use three elds (u; d; s") and reduce the tastes to one per avor by taking 4 p Det. We call these 2 + 1" avor simulations since we take m u = m d m ` . MILC data for m vs. quark mass show clear deviations from linearity, as expected from chiral logarithms. However, the detailed behavior at a 0:13 fm does not agree with continuum chi talk presented by C. Bernard at Lattice 2002; to be published in the proceedings ral perturbation theory (PT) [4]. Figure 1 shows a t to the continuum forms for m X =(m 1 + m 2 ), where X = or K, and m 1 , m 2 are quark masses. (We de ne pions" to have m 1 = m 2 and kaons" to have m 2 m phys s and m 1 6= m 2 .) The t is very poor, with a con dence level of 5 10 . To get good ts, one needs to include the O(a tastebreaking eects into the chiral10/2002;  [show abstract] [hide abstract]
ABSTRACT: We present results for $f_B$, $f_{B_s}$, $f_D$, $f_{D_s}$ and their ratios in the presence of two flavors of light sea quarks ($N_f=2$). We use Wilson light valence quarks and Wilson and static heavy valence quarks; the sea quarks are simulated with staggered fermions. Additional quenched simulations with nonperturbatively improved clover fermions allow us to improve our control of the continuum extrapolation. For our central values the masses of the sea quarks are not extrapolated to the physical $u$, $d$ masses; that is, the central values are "partially quenched." A calculation using "fatlink clover" valence fermions is also discussed but is not included in our final results. We find, for example, $f_B = 190 (7) (^{+24}_{17}) (^{+11}_{2}) (^{+8}_{0})$ MeV, $f_{B_s}/f_B = 1.16 (1) (2) (2) (^{+4}_{0})$, $f_{D_s} = 241 (5) (^{+27}_{26}) (^{+9}_{4}) (^{+5}_{0})$ MeV, and $f_{B}/f_{D_s} = 0.79 (2) (^{+5}_{4}) (3) (^{+5}_{0})$, where in each case the first error is statistical and the remaining three are systematic: the error within the partially quenched $N_f=2$ approximation, the error due to the missing strange sea quark and to partial quenching, and an estimate of the effects of chiral logarithms at small quark mass. The last error, though quite significant in decay constant ratios, appears to be smaller than has been recently suggested by Kronfeld and Ryan, and Yamada. We emphasize, however, that as in other lattice computations to date, the lattice $u,d$ quark masses are not very light and chiral log effects may not be fully under control.Physical review D: Particles and fields 07/2002;  [show abstract] [hide abstract]
ABSTRACT: We present preliminary results for the heavylight leptonic decay constants in the presence of three light dynamical flavors. We generate dynamical configurations with improved staggered and gauge actions and analyze them for heavylight physics with tadpole improved clover valence quarks. When the scale is set by $m_\rho$, we find an increase of approximately 23% in $f_B$ with three dynamical flavors over the quenched case. Discretization errors appear to be small (of order 3% or less) in the quenched case but have not yet been measured in the dynamical case.Nuclear Physics B  Proceedings Supplements 11/2001; · 0.88 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: a Symanzik improved glue [2,3]. This action has small discretization errors for many quantities [4,5]. For the valence quarks, we employ a tadpoleimproved (Landau link) clover action and the Fermilab formalism [6]. The analysis is done in a "partially quenched" manner: the valence quark masses are extrapolated to their physical values with the sea quark masses held fixed. The chiral extrapolation of the sea quark masses (at fixed lattice spacing) is performed afterwards. presented by C. Bernard Table 1 shows the parameters of our lattices and the current state of this project. As we decrease the dynamical quark masses from large values in the threeflavor case, we keep the three masses degenerate until the physical strange quark mass is reached. We then keep the strange quark mass fixed as we further decrease m u;d . Configurations with varying dynamical quark mass (including quenched and twoflavor configurations) have been matched in lattice spacing using the quantity r 111/2001;  [show abstract] [hide abstract]
ABSTRACT: We present preliminary results [1] from exploring the phase diagram of finite temperature QCD with three degenerate flavors and with two light flavors and the mass of the third held approximately at the strange quark mass. We use an order α2sa2, a4 Symanzik improved gauge action and an order αsa2, a4 improved staggered quark action. The improved staggered action leads to a dispersion relation with diminished lattice artifacts, and hence better thermodynamic properties. It decreases the flavor symmetry breaking of staggered quarks substantially, and we estimate that at the transition temperature for an Nt = 8 to Nt = 10 lattice all pions will be lighter than the lightest kaon. Preliminary results on lattices with Nt = 4, 6 and 8 are presented.Nuclear Physics A 11/2001; · 1.53 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: The separation of a heavy quark and antiquark pair leads to the formation of a tube of flux, or "string", which should break in the presence of light quarkantiquark pairs. This expected zerotemperature phenomenon has proven elusive in simulations of lattice QCD. We study mixing between the string state and the twomeson decay channel in QCD with two flavors of dynamical sea quarks. We confirm that mixing is weak and find that it decreases at level crossing. While our study does not show direct effects of internal quark loops, our results, combined with unitarity, give clear confirmation of string breaking.Physical Review D 04/2001; · 4.69 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We calculate the inclusive cross section for prompt photon production in heavyion collisions at RHIC energies (√s=130 GeV and √s=200 GeV) in the central rapidity region including nexttoleading order, O(αemαs2), radiative corrections, initial state nuclear shadowing, and parton energy loss effects. We show that there is a significant suppression of the nuclear cross section, up to ∼30% at √s=200 GeV, due to shadowing and medium induced parton energy loss effects. We find that the nexttoleading order contributions are large and have a strong pt dependence.Physical Review C 04/2001; 63(4). · 3.72 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We present a detailed study of prompt photon production cross section in heavyion collisions in the central rapidity region at energy of $\sqrt{s}=5.5$ TeV, appropriate to LHC experiment. We include the nexttoleading order radiative corrections, $O(\alpha_{em}\alpha_s^2)$, nuclear shadowing and the parton energy loss effects. We find that the nuclear effects can reduce the invariant cross section for prompt photon production by an order of magnitude at $p_t=3$ GeV. We discuss theoretical uncertainties due to parton energy loss and nuclear shadowing parameters. We show that the Kfactor, which signifies the importance of nexttoleading order corrections, is large and has a strong $p_t$ dependence. Comment: version accepted for publication in Nucl. Phys. ANuclear Physics A 01/2001; · 1.53 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We present results for pseudoscalar decay constants of heavylight mesons using both quenched and Nf = 2 dynamical fermion configurations. A variety of fermion actions is investigated: Wilson, nonperturbative clover, and fatlink clover. For heavy quarks the Fermilab formalism is applied. In the quenched approximation, results with the nonperturbatively improved clover action of the Alpha collaboration allow us to study the systematic error of the continuum extrapolation from the Wilson action. In addition, we use quenched configurations to explore the effects of fattening. The lessons from the quenched analyses are then applied to data with dynamical fermions, where both Wilson and fatlink clover actions have been used. This allows us to attempt a continuum extrapolation of the dynamical results.Nuclear Physics B  Proceedings Supplements 12/2000; · 0.88 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We have been studying effects of dynamical quarks on various hadronic observables, using our recently formulated improvement for staggered fermions. To illustrate improvement, we show that the light hadron spectrum in the quenched approximation gives remarkably good scaling. We highlight three new results: (1) We find no apparent quark loop effects in the Edinburgh plot with 2+1 flavors of dynamical quarks at a = 0.14 fm. (2) We show that dynamical quarks modify the shape of the heavy quark potential. (3) We present results hinting at meson decay effects in light hadron spectroscopy.Nuclear Physics B  Proceedings Supplements 11/2000; · 0.88 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: The separation of a heavy quark and antiquark pair leads to the formation of a tube of flux, or "string", which should break in the presence of light quarkantiquark pairs. This expected zerotemperature phenomenon has proven elusive in simulations of lattice QCD. In an extension of work reported last year we present clear evidence for string breaking in QCD with two flavors of dynamical staggered sea quarks and apply our results to a simple threestate mixing model for string breaking. We find that mixing is weak and falls to zero at level crossing.Nuclear Physics B  Proceedings Supplements 11/2000; · 0.88 Impact Factor 
Article: Prompt photons at RHIC
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ABSTRACT: We calculate the inclusive cross section for prompt photon production in heavyion collisions at RHIC energies ($\sqrt{s}=130$ GeV and $\sqrt{s}=200$ GeV) in the central rapidity region including nexttoleading order, $O(\alpha_{em}\alpha_s^2)$, radiative corrections, initial state nuclear shadowing and parton energy loss effects. We show that there is a significant suppression of the nuclear cross section, up to $\sim 30%$ at $\sqrt{s}=200$ GeV, due to shadowing and medium induced parton energy loss effects. We find that the nexttoleading order contributions are large and have a strong $p_t$ dependence. Comment: 9 pages, 5 figures, expanded discussion of the K factor10/2000;
Publication Stats
420  Citations  
82  Downloads  
1k  Views  
30.07  Total Impact Points  
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Institutions

2005

College of William and Mary
 Department of Physics
Williamsburg, VA, United States


1998–2005

Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, MA, United States 
The University of Arizona
 Department of Physics
Tucson, Arizona, United States


1994–2005

Boston University
 Department of Physics
Boston, MA, United States


1995

Brown University
 Department of Physics
Providence, Rhode Island, United States
