Publications (110)134.34 Total impact
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ABSTRACT: The form factor that yields the lightbylight scattering contribution to the muon anomalous magnetic moment is computed in lattice QCD+QED and QED. A nonperturbative treatment of QED is used and is checked against perturbation theory. The hadronic contribution is calculated for unphysical quark and muon masses, and only the diagram with a single quark loop is computed. Statistically significant signals are obtained. Initial results appear promising, and the prospect for a complete calculation with physical masses and controlled errors is discussed.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Neutral $B$ meson mixing matrix elements and $B$ meson decay constants are calculated. Static approximation is used for $b$ quark and domainwall fermion formalism is employed for light quarks. The calculations are carried out on $2+1$ flavor dynamical ensembles generated by RBC/UKQCD Collaborations with lattice spacings $0.086$fm ($a^{1}\sim 2.3$GeV) and $0.11$fm ($1.7$GeV), and a fixed physical spatial volume of about $(2.7{\rm fm})^3$. In the static quark action, linksmearings are used to improve the signaltonoise ratio. We employ two kinds of linksmearings, HYP1 and HYP2, and their results are combined in taking the continuum limit. For the matching between the lattice and the continuum theory, oneloop perturbative $O(a)$ improvements are made to reduce discretization errors. As the most important quantity of this work, we obtain SU(3) breaking ratio $\xi=1.208(60)$, where the error includes statistical and systematic one. We also find other neutral $B$ meson mixing quantities $f_B\sqrt{\hat{B}_B}=240(22)$MeV, $f_{B_s}\sqrt{\hat{B}_{B_s}}=290(22)$MeV, $\hat{B}_B=1.17(22)$, $\hat{B}_{B_s}=1.22(13)$ and $B_{B_s}/B_B=1.028(74)$, $B$ meson decay constants $f_B=219(17)$MeV, $f_{B_s}=264(19)$MeV and $f_{B_s}/f_B=1.193(41)$, in the static limit of $b$ quark.06/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We report on the first complete calculation of the $K_LK_S$ mass difference, $\Delta M_K$, using lattice QCD. The calculation is performed on a 2+1 flavor, domain wall fermion (DWF) ensemble with a 330~MeV pion mass and a 575~MeV kaon mass. We use a quenched charm quark with a 949~MeV mass to implement GlashowIliopoulosMaiani (GIM) cancellation. For these heavierthanphysical particle masses, we obtain $\Delta M_K =3.19(41)(96)\times 10^{12}$~MeV, quite similar to the experimental value. Here the first error is statistical and the second is an estimate of the systematic discretization error. An interesting aspect of this calculation is the importance of the disconnected diagrams, a dramatic failure of the OZI rule.06/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the Bmeson decay constants f_B, f_Bs, and their ratio in unquenched lattice QCD using domainwall light quarks and relativistic bquarks. We use gaugefield ensembles generated by the RBC and UKQCD collaborations using the domainwall fermion action and Iwasaki gauge action with three flavors of light dynamical quarks. We analyze data at two lattice spacings of a ~ 0.11, 0.086 fm with unitary pion masses as light as M_pi ~ 290 MeV; this enables us to control the extrapolation to the physical lightquark masses and continuum. For the bquarks we use the anisotropic clover action with the relativistic heavyquark interpretation, such that discretization errors from the heavyquark action are of the same size as from the lightquark sector. We renormalize the lattice heavylight axialvector current using a mostly nonperturbative method in which we compute the bulk of the matching factor nonperturbatively, with a small correction, that is close to unity, in lattice perturbation theory. We also improve the lattice heavylight current through O(alpha_s a). We extrapolate our results to the physical lightquark masses and continuum using SU(2) heavymeson chiral perturbation theory, and provide a complete systematic error budget. We obtain f_B0 = 196.2(15.7) MeV, f_B+ = 195.4(15.8) MeV, f_Bs = 235.4(12.2) MeV, f_Bs/f_B0 = 1.193(59), and f_Bs/f_B+ = 1.220(82), where the errors are statistical and total systematic added in quadrature. These results are in good agreement with other published results and provide an important independent cross check of other threeflavor determinations of Bmeson decay constants using staggered light quarks.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The real and imaginary parts of the $K_LK_S$ mixing matrix receive contributions from all three charge2/3 quarks: up, charm and top. These give both short and longdistance contributions which are accessible through a combination of perturbative and lattice methods. We will discuss a strategy to compute both the mass difference, $\Delta M_K$ and $\epsilon_K$ to subpercent accuracy, looking in detail at the contributions from each of the three CKM matrix element products $V_{id}^*V_{is}$ for $i=u, c$ and $t$ as described in Ref. [1]02/2014; 
Article: Covariant approximation averaging
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ABSTRACT: We present a new class of statistical error reduction techniques for MonteCarlo simulations. Using covariant symmetries, we show that correlation functions can be constructed from inexpensive approximations without introducing any systematic bias in the final result. We introduce a new class of covariant approximation averaging techniques, known as allmode averaging (AMA), in which the approximation takes account of contributions of all eigenmodes through the inverse of the Dirac operator computed from the conjugate gradient method with a relaxed stopping condition. In this paper we compare the performance and computational cost of our new method with traditional methods using correlation functions and masses of the pion, nucleon, and vector meson in $N_f=2+1$ lattice QCD using domainwall fermions. This comparison indicates that AMA significantly reduces statistical errors in MonteCarlo calculations over conventional methods for the same cost.02/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Neutral B meson mixing matrix elements and B meson decay constants are calculated. Static approximation is used for b quark and domainwall fermion formalism is employed for light quarks. The calculations are done on 2+1 flavor dynamical ensembles, whose lattice spacings are 0.086 fm and 0.11 fm with a fixed physical spatial volume of about (2.7 fm)^3. In the static quark action, linksmearings are used to improve the signaltonoise ratio. We employ two kinds of linksmearings and their results are combined in taking a continuum limit. For the matching between the lattice and the continuum theory, oneloop perturbative calculations are used including O(a) improvements to reduce discretization errors. We obtain SU(3) braking ratio \xi=1.222(60) in the static limit of b quark.12/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We report on a calculation of the effects of isospin breaking in Lattice QCD+QED. This involves using Chiral Perturbation Theory with Electromagnetic corrections to find the renormalized, nondegenerate, light quark masses. The calculations are carried out on QCD ensembles generated by the RBC and UKQCD collaborations using Domain Wall Fermions and the Iwasaki and Iwasaki+DSDR Gauge Actions with unitary pion masses down to 170 MeV. Noncompact QED is treated in the quenched approximation. The simulations use a $32^3$ lattice size with $a^{1}=2.28(3)$ GeV (Iwasaki) and 1.37(1) (Iwasaki+DSDR). This builds on previous work from the RBC/UKQCD collaboration with lattice spacing $a^{1}=1.78(4)$ GeV.12/2013; 
Conference Paper: The origin of mass
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ABSTRACT: The origin of mass is one of the deepest mysteries in science. Neutrons and protons, which account for almost all visible mass in the Universe, emerged from a primordial plasma through a cataclysmic phase transition microseconds after the Big Bang. However, most mass in the Universe is invisible. The existence of dark matter, which interacts with our world so weakly that it is essentially undetectable, has been established from its galacticscale gravitational effects. Here we describe results from the first truly physical calculations of the cosmic phase transition and a groundbreaking firstprinciples investigation into composite dark matter, studies impossible with previous stateoftheart methods and resources. By inventing a powerful new algorithm, "DSDR," and implementing it effectively for contemporary supercomputers, we attain excellent strong scaling, perfect weak scaling to the LLNL BlueGene/Q two million cores, sustained speed of 7.2 petaflops, and timetosolution speedup of more than 200 over the previous stateoftheart.Proceedings of the International Conference on High Performance Computing, Networking, Storage and Analysis; 11/2013  [Show abstract] [Hide abstract]
ABSTRACT: After a brief selfcontained introduction to the muon anomalous magnetic moment, (g2), we review the status of lattice calculations of the hadronic vacuum polarization contribution and present first results from lattice QCD for the hadronic lightbylight scattering contribution. The signal for the latter is consistent with model calculations. While encouraging, the statistical error is large and systematic errors are mostly uncontrolled. The method is applied first to pure QED as a check.01/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We develop and demonstrate techniques needed to compute the long distance contribution to the $K_{L}$$K_{S}$ mass difference, $\Delta M_K$, in lattice QCD and carry out a first, exploratory calculation of this fundamental quantity. The calculation is performed on 2+1 flavor, domain wall fermion, $16^3\times32$ configurations with a 421 MeV pion mass. We include only currentcurrent operators and drop all disconnected and double penguin diagrams. The short distance part of the mass difference in a 2+1 flavor calculation contains a quadratic divergence cut off by the lattice spacing. Here, this quadratic divergence is eliminated through the GIM mechanism by introducing a valence charm quark. The inclusion of the charm quark makes the complete calculation accessible to lattice methods provided the discretization errors associated with the charm quark can be controlled. The long distance effects are discussed for each parity channel separately. While we can see a clear signal in the parity odd channel, the signal to noise ratio in the parity even channel is exponentially decreasing as the separation between the two weak operators increases. We obtain a mass difference $\Delta M_K$ which ranges from $5.12(24)\times 10^{12}$ MeV to $9.31(66)\times 10^{12}$ MeV for kaon masses varying from 563 MeV to 839 MeV. Extensions of these methods are proposed which promise accurate results for both $\Delta M_K$ and $\epsilon_K$, including long distance effects.Physical review D: Particles and fields 12/2012; 88(1). 
Article: Error reduction technique using covariant approximation and application to nucleon form factor
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ABSTRACT: We demonstrate the new class of variance reduction techniques for hadron propagator and nucleon isovector form factor in the realistic lattice of $N_f=2+1$ domainwall fermion. Allmode averaging (AMA) is one of the powerful tools to reduce the statistical noise effectively for wider varieties of observables compared to existing techniques such as lowmode averaging (LMA). We adopt this technique to hadron twopoint functions and threepoint functions, and compare with LMA and traditional sourceshift method in the same ensembles. We observe AMA is much more cost effective in reducing statistical error for these observables.12/2012;  [Show abstract] [Hide abstract]
ABSTRACT: We describe the computation of the amplitude A2 for a kaon to decay into two pions with isospin I=2. The results presented in [ T. Blum et al. Phys. Rev. Lett. 108 141601 (2012)] from an analysis of 63 gluon configurations are updated to 146 configurations giving ReA2=1.381(46)stat(258)syst108 GeV and ImA2=6.54(46)stat(120)syst1013 GeV. ReA2 is in good agreement with the experimental result, whereas the value of ImA2 was hitherto unknown. We are also working toward a direct computation of the K→(ππ)I=0 amplitude A0 but, within the Standard Model, our result for ImA2 can be combined with the experimental results for ReA0, ReA2 and ε′/ε to give ImA0/ReA0=1.61(28)×104. Our result for ImA2 implies that the electroweak penguin (EWP) contribution to ε′/ε is Re(ε′/ε)EWP=(6.25±0.44stat±1.19syst)×104.Physical review D: Particles and fields 10/2012; 86(7).  Progress of Theoretical and Experimental Physics. 08/2012;
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ABSTRACT: We present physical results for a variety of light hadronic quantities obtained via a combined analysis of three 2+1 flavour domain wall fermion ensemble sets. For two of our ensemble sets we used the Iwasaki gauge action with beta=2.13 (a^1=1.75(4) GeV) and beta=2.25 (a^1=2.31(4) GeV) and lattice sizes of 24^3 x 64 and 32^3 x 64 respectively, with unitary pion masses in the range 293(5)417(10) MeV. The extent L_s for the 5^th dimension of the domain wall fermion formulation is L_s=16 in these ensembles. In this analysis we include a third ensemble set that makes use of the novel Iwasaki+DSDR (Dislocation Suppressing Determinant Ratio) gauge action at beta = 1.75 (a^1=1.37(1) GeV) with a lattice size of 32^3 x 64 and L_s=32 to reach down to partiallyquenched pion masses as low as 143(1) MeV and a unitary pion mass of 171(1) MeV, while retaining good chiral symmetry and topological tunneling. We demonstrate a significant improvement in our control over the chiral extrapolation, resulting in much improved continuum predictions for the above quantities. The main results of this analysis include the pion and kaon decay constants, f_\pi=127(3)_{stat}(3)_{sys} MeV and f_K = 152(3)_{stat}(2)_{sys} MeV respectively (f_K/f_\pi = 1.199(12)_{stat}(14)_{sys}); the average up/down quark mass and the strangequark mass in the MSbarscheme at 3 GeV, m_{ud}(MSbar, 3 GeV) = 3.05(8)_{stat}(6)_{sys} MeV and m_s(MSbar, 3 GeV) = 83.5(1.7)_{stat}(1.1)_{sys}; the neutral kaon mixing parameter in the MSbarscheme at 3 GeV, B_K(MSbar,3 GeV) = 0.535(8)_{stat}(13)_{sys}, and in the RGI scheme, \hat B_K = 0.758(11)_{stat}(19)_{sys}; and the Sommer scales r_1 = 0.323(8)_{stat}(4)_{sys} fm and r_0 = 0.480(10)_{stat}(4)_{sys} (r_1/r_0 = 0.673(11)_{stat}(3)_{sys}). We also obtain values for the SU(2) ChPT effective couplings, \bar{l_3} = 2.91(23)_{stat}(7)_{sys}$ and \bar{l_4} = 3.99(16)_{stat}(9)_{sys}.Physical review D: Particles and fields 08/2012;  [Show abstract] [Hide abstract]
ABSTRACT: We present a general class of unbiased improved estimators for physical observables in lattice gauge theory computations which significantly reduces statistical errors at modest computational cost. The error reduction techniques, referred to as covariant approximation averaging, utilize approximations which are covariant under lattice symmetry transformations. We observed cost reductions from the new method compared to the traditional one, for fixed statistical error, of 16 times for the nucleon mass at $M_\pi\sim 330$ MeV (DomainWall quark) and 2.620 times for the hadronic vacuum polarization at $M_\pi\sim 480$ MeV (Asqtad quark). These cost reductions should improve with decreasing quark mass and increasing lattice sizes.Physical Review D 08/2012; · 4.69 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the masses of bottom mesons using an improved relativistic action for the bquarks and the RBC/UKQCD Iwasaki gauge configurations with 2+1 flavors of dynamical domainwall light quarks. We analyze configurations with two lattice spacings: a^{1} = 1.729 GeV (a ~ 0.11 fm) and a^{1} = 2.281 GeV (a ~ 0.086 fm). We use an anisotropic, cloverimproved Wilson action for the bquark, and tune the three parameters of the action nonperturbatively such that they reproduce the experimental values of the B_s and B_s* heavylight meson states. The masses and masssplittings of the lowlying bottomonium states (such as the eta_b and Upsilon) can then be computed with no additional inputs, and comparison between these predictions and experiment provides a test of the validity of our method. We obtain bottomonium masses with total uncertainties of ~0.50.6% and finestructure splittings with uncertainties of ~3545%; for all cases we find good agreement with experiment. The parameters of the relativistic heavyquark action tuned for bquarks presented in this work can be used for precise calculations of weak matrix elements such as Bmeson decay constants and mixing parameters with lattice discretization errors that are of the same size as in light pseudoscalar meson quantities. This general method can also be used for charmed meson masses and matrix elements if the parameters of the heavyquark action are appropriately tuned.Physical review D: Particles and fields 06/2012; 86(11).  [Show abstract] [Hide abstract]
ABSTRACT: We report on the first realistic ab initio calculation of a hadronic weak decay, that of the amplitude A(2) for a kaon to decay into two π mesons with isospin 2. We find ReA(2)=(1.436±0.063(stat)±0.258(syst))10(8) GeV in good agreement with the experimental result and for the hitherto unknown imaginary part we find ImA(2)=(6.83±0.51(stat)±1.30(syst))10(13) GeV. Moreover combining our result for ImA(2) with experimental values of ReA(2), ReA(0), and ε'/ε, we obtain the following value for the unknown ratio ImA(0)/ReA(0) within the standard model: ImA(0)/ReA(0)=1.63(19)(stat)(20(syst)×10(4). One consequence of these results is that the contribution from ImA(2) to the direct CP violation parameter ε' (the socalled Electroweak Penguin contribution) is Re(ε'/ε)(EWP)=(6.52±0.49(stat)±1.24(syst))×10(4). We explain why this calculation of A(2) represents a major milestone for lattice QCD and discuss the exciting prospects for a full quantitative understanding of CP violation in kaon decays.Physical Review Letters 04/2012; 108(14):141601. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We report on the first realistic ab initio calculation of a hadronic weak decay, that of the amplitude A2 for a kaon to decay into two π mesons with isospin 2. We find ReA2=(1.436±0.063stat±0.258syst)108 GeV in good agreement with the experimental result and for the hitherto unknown imaginary part we find ImA2=(6.83±0.51stat±1.30syst)1013 GeV. Moreover combining our result for ImA2 with experimental values of ReA2, ReA0, and ϵ′/ϵ, we obtain the following value for the unknown ratio ImA0/ReA0 within the standard model: ImA0/ReA0=1.63(19)stat(20)syst×104. One consequence of these results is that the contribution from ImA2 to the direct CP violation parameter ϵ′ (the socalled Electroweak Penguin contribution) is Re(ϵ′/ϵ)EWP=(6.52±0.49stat±1.24syst)×104. We explain why this calculation of A2 represents a major milestone for lattice QCD and discuss the exciting prospects for a full quantitative understanding of CP violation in kaon decays.Physical Review Letters 04/2012; 108(14). · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The effect of sea quark electromagnetic charge on meson masses is investigated, and first results for full QED+QCD lowenergy constants are presented. The electromagnetic charge for sea quarks is incorporated in quenched QED+full QCD lattice simulations by a reweighting method. The reweighting factor, which connects quenched and unquenched QED, is estimated using a stochastic method on 2+1 flavor dynamical domainwall quark ensembles.Physical Review Letters 02/2012; 109(7). · 7.73 Impact Factor
Publication Stats
2k  Citations  
134.34  Total Impact Points  
Top Journals
Institutions

2002–2012

Brookhaven National Laboratory
 Physics Department
New York City, New York, United States


2010

Columbia University
 Department of Physics
New York City, NY, United States


2008

The University of Edinburgh
 School of Physics and Astronomy
Edinburgh, SCT, United Kingdom


2000–2008

Kanazawa University
 • Institute for Theoretical Physics
 • Department of Physics
Kanazawa, Ishikawa, Japan


2005–2006

RIKEN
Вако, Saitama, Japan


1998

University of Tsukuba
 Centre for Computational Sciences
Tsukuba, Ibarakiken, Japan


1996

Nagoya University
Nagoya, Aichi, Japan
