B Leptonic Decays and B- bar B Mixing with 2+1 Flavors of Dynamical Quarks

Calculations of B leptonic decays and B- bar B mixing using NRQCD heavy and Asqtad light valence quarks on the MILC dynamical configurations are described. Smearing has been implemented to substantially reduce the statistical errors of the matrix elements needed for the determination of f_B. The four-fermion matrix elements needed for the determination of f_{B_s}^2B_{B_s} have been calculated and a preliminary result is given.Comment: 3 pages, 3 figures, talk given at Lattice2004(heavy), Batavia, Illinois, 21-26 Jun 200

Ex Vivo Culture of Chick Cerebellar Slices and Spatially Targeted Electroporation of Granule Cell Precursors

The cerebellar external granule layer (EGL) is the site of the largest transit amplification in the developing brain, and an excellent model for studying neuronal proliferation and differentiation. In addition, evolutionary modifications of its proliferative capability have been responsible for the dramatic expansion of cerebellar size in the amniotes, making the cerebellum an excellent model for evo-devo studies of the vertebrate brain. The constituent cells of the EGL, cerebellar granule progenitors, also represent a significant cell of origin for medulloblastoma, the most prevalent paediatric neuronal tumour. Following transit amplification, granule precursors migrate radially into the internal granular layer of the cerebellum where they represent the largest neuronal population in the mature mammalian brain. In chick, the peak of EGL proliferation occurs towards the end of the second week of gestation. In order to target genetic modification to this layer at the peak of proliferation, we have developed a method for genetic manipulation through ex vivo electroporation of cerebellum slices from embryonic Day 14 chick embryos. This method recapitulates several important aspects of in vivo granule neuron development and will be useful in generating a thorough understanding of cerebellar granule cell proliferation and differentiation, and thus of cerebellum development, evolution and disease

Heavy-Light Meson Semileptonic Decays with Staggered Light Quarks

We report on exploratory studies of heavy-light meson semileptonic decays using Asqtad light quarks, NRQCD heavy quarks and Symanzik improved glue on coarse quenched lattices. Oscillatory contributions to three-point correlators coming from the staggered light quarks are found to be handled well by Bayesian fitting methods. B meson decays to both the Goldstone pion and to one of the point-split non-Goldstone pions are investigated. One-loop perturbative matching of NRQCD/Asqtad heavy-light currents is incorporated.Comment: 3 pages, 3 postscript figures, Lattice2003(heavy

The B Meson Decay Constant from Unquenched Lattice QCD

We present determinations of the B meson decay constant f_B and of the ratio f_{B_s}/f_B using the MILC collaboration unquenched gauge configurations which include three flavors of light sea quarks. The mass of one of the sea quarks is kept around the strange quark mass, and we explore a range in masses for the two lighter sea quarks down to m_s/8. The heavy b quark is simulated using Nonrelativistic QCD, and both the valence and sea light quarks are represented by the highly improved (AsqTad) staggered quark action. The good chiral properties of the latter action allow for a much smoother chiral extrapolation to physical up and down quarks than has been possible in the past. We find f_B = 216(9)(19)(4) (6) MeV and f_{B_s} /f_B = 1.20(3)(1).Comment: 4 pages, 2 figure

Beyond spatial scalability limitations with a massively parallel method for linear oscillatory problems

This is the author accepted manuscript. The final version is available from SAGE Publications via the DOI in this record.This paper presents, discusses and analyses a massively parallel-in-time solver for linear oscillatory PDEs, which is a key numerical component for evolving weather, ocean, climate and seismic models. The time parallelization in this solver allows us to significantly exceed the computing resources used by parallelization-in-space methods and results in a correspondingly significantly reduced wall-clock time. One of the major difficulties of achieving Exascale performance for weather prediction is that the strong scaling limit – the parallel performance for a fixed problem size with an increasing number of processors – saturates. A main avenue to circumvent this problem is to introduce new numerical techniques that take advantage of time parallelism. In this paper we use a time-parallel approximation that retains the frequency information of oscillatory problems. This approximation is based on (a) reformulating the original problem into a large set of independent terms and (b) solving each of these terms independently of each other which can now be accomplished on a large number of HPC resources. Our results are conducted on up to 3586 cores for problem sizes with the parallelization-in-space scalability limited already on a single node. We gain significant reductions in the time-to-solution of 118.3 for spectral methods and 1503.0 for finite-difference methods with the parallelizationin-time approach. A developed and calibrated performance model gives the scalability limitations a-priory for this new approach and allows us to extrapolate the performance method towards large-scale system. This work has the potential to contribute as a basic building block of parallelization-in-time approaches, with possible major implications in applied areas modelling oscillatory dominated problems.The authors gratefully acknowledge the Gauss Centre for Supercomputing e.V. (www.gauss-centre.eu) for funding this project by providing computing time on the GCS Supercomputer SuperMUC at Leibniz Supercomputing Centre (LRZ, www.lrz. de). We also acknowledge use of Hartree Centre resources in this work on which the early evaluation of the parallelization concepts were done

The k=2 string tension in four dimensional SU(N) gauge theories

We calculate the k=2 string tensions in SU(4) and SU(5) gauge theories in 3+1 dimensions, and compare them to the k=1 fundamental string tensions. We find, from the continuum extrapolation of our lattice calculations, that K(k=2)/K(k=1) = 1.40(8) in the SU(4) gauge theory, and that K(k=2)/K(k=1) = 1.56(10) in SU(5). We remark upon the way this might constrain the dynamics of confinement and the intriguing implications it might have for the mass spectrum of SU(N) gauge theories. We also note that these results agree closely with the MQCD-inspired conjecture that the SU(N) string tensions satisfy K(k)/K(1) = sin(k.pi/N)/sin(pi/N).Comment: 10 page

The Upsilon spectrum and m_b from full lattice QCD

We show results for the Upsilon spectrum calculated in lattice QCD including for the first time vacuum polarization effects for light u and d quarks as well as s quarks. We use gluon field configurations generated by the MILC collaboration. The calculations compare the results for a variety of u and d quark masses, as well as making a comparison to quenched results (in which quark vacuum polarisation is ignored) and results with only u and d quarks. The b quarks in the Upsilon are treated in lattice Nonrelativistic QCD through NLO in an expansion in the velocity of the b quark. We concentrate on accurate results for orbital and radial splittings where we see clear agreement with experiment once u, d and s quark vacuum polarisation effects are included. This now allows a consistent determination of the parameters of QCD. We demonstrate this consistency through the agreement of the Upsilon and B spectrum using the same lattice bare b quark mass. A one-loop matching to continuum QCD gives a value for the b quark mass in full lattice QCD for the first time. We obtain m_b^{\bar{MS}}(m_b^{\bar{MS}}) = 4.4(3) GeV. We are able to give physical results for the heavy quark potential parameters, r_0 = 0.469(7) fm and r_1 = 0.321(5) fm. Results for the fine structure in the spectrum and the Upsilon leptonic width are also presented. We predict the Upsilon - eta_b splitting to be 61(14) MeV, the Upsilon^{\prime} - eta_b^{\prime} splitting as 30(19) MeV and the splitting between the h_b and the spin-average of the chi_b states to be less than 6 MeV. Improvements to these calculations that will be made in the near future are discussed.Comment: 24 pages, 19 figures. Version to be published. Minor changes made and typographical errors corrected. Experimental leptonic widths updated in section