Lattice-Constrained Parametrizations of Form Factors for Semileptonic and Rare Radiative B Decays

We describe the form factors for semileptonic B to rho l nu and radiative B to K* gamma decays with just two parameters and the two form factors for semileptonic B to pi l nu decays with three parameters. The parametrizations are constrained by lattice results and are consistent with heavy quark symmetry, kinematic constraints and light cone sum rule scaling relations.Comment: 3 pages, latex, 2 eps files, uses epsf.sty and espcrc2.sty, poster presented at Lattice 97, Edinburgh, 22-26 July 199

An Investigation of the Soft Pion Relation in Quenched Lattice QCD

A lattice determination of the form factor and decay constants for the semileptonic decay of heavy pseudoscalar (PS) mesons at zero recoil is presented from which the soft pion relation is satisfied. Chiral extrapolation of the form factor is performed at constant $q^2$. Pole dominance is used to extrapolate the form factor in heavy quark mass. At the B mass, the form factor at zero recoil lies somewhat below the ratio of decay constants; the relation remains satisfied within error.Comment: 3 pages, 2 figure

First Lattice Study of the Form Factors A_0 and A_3 in the Decay Bbar^0 to rho^+ l^- nubar_l

We report on a lattice calculation of the form factors A_0 and A_3 for the pseudoscalar to vector meson semileptonic decay Bbar^0 to rho^+ l^- nubar_l. We find that resonant (or pole-type) contributions alone are unable to describe these two form factors simultaneously. For the quantity A_0(q^2=0), which is important phenomenologically for the determination of |Vub|, we extract a range of values, A_0(q^2=0) = (0.16--0.35) +0.09-0.06, where the range is due to systematic uncertainty and the quoted error is statistical. We have also determined A_2(q^2=0) = 0.28 +0.09-0.06 +0.04-0.05.Comment: 14 pages LaTeX209 with 5 figures from 11 encapsulated PostScript files, using epsf.sty. Also available from http://wwwhep.phys.soton.ac.uk/hepwww/papers/shep9601

Changes in toxin content, biomass and pigments of the dinoflagellate Alexandrium minutum during nitrogen refeeding and growth into nitrogen or phosphorus stress

Two strains oi the paralytic shellfish toxin (PST) producing dinoflagellate Alexandrium minutum Halim (highly toxic ALl V and weakly toxic AL2V) were grown in batch culture with either nitrate or phosphate as the limiting nutrient. In comparison with cells of the strain AL1V, cells of AL2V grew at a similar C-specific Tale, had a higher C/N ratio, and lower ratios of chl a/chl C2and chl a/peridinin. Neither chlorophylls flor carotenoids could be used to estimate C-biomass, N-biomass or toxin content for this organismo The toxin profile for both strains was dominated (up to 95 %) by the gonyautoxin GTX4, with smaller proportions of GTX1, GTX2 and GTX3. The Tale of toxin synthesis for both strains was greatest 1 to 2 d after the N-refeeding of N-deprived cells, with the net Tale of toxin syn- .thesis exceeding that of C-biomass and cell division by a factor of up to 4. Toxin synthesis was not enhanced by short-term P-stress. N-stress alone led to a decrease in toxin cell-I, but P-stress followed by N-stress did not result in such a decline, implicating phosphorus in the regulation of toxin metabolism. Although arginine is a majar precursor for PST synthesis, taurine, glycine, glutamine, and cell N showed similar relations to that observed for arginine with respect to toxin contento Furthermore, the mole ratio of arginine/toxin could vary by a factor of up to 5 between AL1V and AL2V at peak values of toxin cell-1, and by more than 5 within a strain when growing under different conditions. These observations suggest that the relationship between free arginine content and toxin content is complex. No explanation for the higher toxin content of AL1V is apparent, except that AL1V has a higher N-content per cell and this may be conducive to a higher Tale of synthesis of the N-rich toxins.Publicado

A Numerical Study of Partially Twisted Boundary Conditions

We investigate the use of partially twisted boundary conditions in a lattice simulation with two degenerate flavours of improved Wilson sea quarks. The use of twisted boundary conditions on a cubic volume (L^3) gives access to components of hadronic momenta other than integer multiples of 2*pi/L. Partial twisting avoids the need for new gluon configurations for every choice of momentum, while, as recently demonstrated, keeping the finite-volume errors exponentially small for the physical quantities investigated in this letter. In this study we focus on the spectrum of pseudo scalar and vector mesons, on their leptonic decay constants and on Z_P, the matrix element of the pseudo scalar density between the pseudo scalar meson and the vacuum. The results confirm the momentum shift imposed by these boundary conditions and in addition demonstrate that they do not introduce any appreciable noise. We therefore advocate the use of partially twisted boundary conditions in applications where good momentum resolution is necessary.Comment: 10 pages, 3 figure

The pion's electromagnetic form factor at small momentum transfer in full lattice QCD

We compute the electromagnetic form factor of a "pion" with mass m_pi=330MeV at low values of Q^2\equiv -q^2, where q is the momentum transfer. The computations are performed in a lattice simulation using an ensemble of the RBC/UKQCD collaboration's gauge configurations with Domain Wall Fermions and the Iwasaki gauge action with an inverse lattice spacing of 1.73(3)GeV. In order to be able to reach low momentum transfers we use partially twisted boundary conditions using the techniques we have developed and tested earlier. For the pion of mass 330MeV we find a charge radius given by _{330MeV}=0.354(31)fm^2 which, using NLO SU(2) chiral perturbation theory, extrapolates to a value of =0.418(31)fm^2 for a physical pion, in agreement with the experimentally determined result. We confirm that there is a significant reduction in computational cost when using propagators computed from a single time-slice stochastic source compared to using those with a point source; for m_pi=330MeV and volume (2.74fm)^3 we find the reduction is approximately a factor of 12.Comment: 20 pages, 3 figure

Lattice Determination of the B∗BπB^\ast B \pi Coupling

The coupling $g_{B^\ast B \pi}$ is related to the form factor at zero momentum of the axial current between $B^\ast$ and $B$ states. Moreover it is related to the effective coupling between heavy mesons and pions that appear the heavy meson chiral Lagrangian. This coupling has been evaluated on the lattice using static heavy quarks and light quark propagators determined by a stochastic inversion of the fermionic bilinear. We found the value $g=0.42(4)(8)$. Beside its theoretical interest, this quantity has phenomenological implications in $B \to \pi + \bar l l$ decays.Comment: Lattice 99, 3 page

Evidence for production of paralytic shellfish toxins by bacteria associated with Alexandrium spp. (Dinophyta) in culture

A substantial proportion of bacteria from five Alexandrium cultures originally isolated from various countries produced sodium channel blocking (SCB) toxins, as ascertained by mouse neuroblastoma assay. The quantities of SCB toxins produced by bacteria and dinoflagellates were noted, and the limitations in comparing the toxicities of these two organisms are discussed. The chemical nature of the SCB toxins in selected bacterial isolates was determined as paralytic shellfish toxins by pre- and postcolumn high-performance liquid chromatography, capillary electrophoresis-mass spectrometry, and enzyme immunoassay.Versión del editor3,829

B-meson decay constants from 2+1-flavor lattice QCD with domain-wall light quarks and relativistic heavy quarks

We calculate the B-meson decay constants fB, fBs, and their ratio in unquenched lattice QCD using domain-wall light quarks and relativistic b quarks. We use gauge-field ensembles generated by the RBC and UKQCD collaborations using the domain-wall 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 Mπ ~ 290 MeV; this enables us to control the extrapolation to the physical light-quark masses and continuum. For the b quarks we use the anisotropic clover action with the relativistic heavy-quark interpretation, such that discretization errors from the heavy-quark action are of the same size as from the light-quark sector. We renormalize the lattice heavy-light axial-vector 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 heavy-light current through O (αsa). We extrapolate our results to the physical light-quark masses and continuum using SU(2) heavy-meson chiral perturbation theory, and provide a complete systematic error budget. We obtain fB0 = 199.5(12.6)  MeV, fB+ = 195.6(14.9)  MeV, fBs = 235.4(12.2)  MeV, fBs/fB0 = 1.197(50), and fBs/fB+ = 1.223(71), 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 three-flavor determinations of B-meson decay constants using staggered light quarks