arXiv subjects

D. Toussaint

Publications and source records attributed to D. Toussaint.

At least 73 records · Page 4Linked to original sources

arXiv2011

B- and D-meson decay constants from three-flavor lattice QCD

We calculate the leptonic decay constants of B_{(s)} and D_{(s)} mesons in lattice QCD using staggered light quarks and Fermilab bottom and charm quarks. We compute the heavy-light meson correlation functions on the MILC asqtad-improved staggered gauge configurations which include the effects of three light dynamical sea quarks. We simulate with several values of the light valence- and sea-quark masses (down to ~m_s/10) and at three lattice spacings (a ~ 0.15, 0.12, and 0.09 fm) and extrapolate to the physical up and down quark masses and the continuum using expressions derived in heavy-light meson staggered chiral perturbation theory. We renormalize the heavy-light axial current using a mostly nonperturbative method such that only a small correction to unity must be computed in lattice perturbation theory and higher-order terms are expected to be small. We obtain f_{B^+} = 196.9(8.9) MeV, f_{B_s} = 242.0(9.5) MeV, f_{D^+} = 218.9(11.3) MeV, f_{D_s} = 260.1(10.8) MeV, and the SU(3) flavor-breaking ratios f_{B_s}/f_{B} = 1.229(26) and f_{D_s}/f_{D} = 1.188(25), where the numbers in parentheses are the total statistical and systematic uncertainties added in quadrature.

hep-lat↗

arXiv2011

Properties of light pseudoscalars from lattice QCD with HISQ ensembles

We fit lattice-QCD data for light-pseudoscalar masses and decay constants, from HISQ configurations generated by MILC, to SU(3) staggered chiral perturbation theory. At present such fits have rather high values of chi^2/d.o.f., possibly due to the lack of ensembles with lighter-than-physical sea strange-quark masses. We propose solutions to this problem for future work. We also perform simple linear interpolations near the physical point on two ensembles with different lattice spacings, and obtain the preliminary result (f_K / f_pi)^phys = 1.1872(41) in the continuum limit.

hep-lat↗

arXiv2011

Tuning Fermilab Heavy Quarks in 2+1 Flavor Lattice QCD with Application to Hyperfine Splittings

We report the non-perturbative tuning of parameters--- kappa_c, kappa_b, and kappa_crit ---that determine the heavy-quark mass in the Fermilab action. This requires the computation of the masses of Ds^(*) and Bs^(*) mesons comprised of a Fermilab heavy quark and a staggered light quark. Additionally, we report the hyperfine splittings for Ds and Bs mesons as a cross-check of our simulation and analysis methods. We find a splitting of 145 +/- 15 MeV for the Ds system and 40 +/- 9 MeV for the Bs system. These are in good agreement with the Particle Data Group average values of 143.9 +/- 0.4 MeV and 46.1 +/- 1.5 MeV, respectively. The calculations are carried out with the MILC 2+1 flavor gauge configurations at three lattice spacings $a$ approximately 0.15, 0.12, and 0.09 fm.

hep-lat↗

arXiv2010

Simulations with dynamical HISQ quarks

We report on the status of a program of generating and using configurations with four flavors of dynamical quarks, using the HISQ action. We study the lattice spacing dependence of physical quantities in these simulations, using runs at several lattice spacings, but with the light quark mass held fixed at two tenths of the strange quark mass. We find that the lattice artifacts in the HISQ simulations are much smaller than those in the asqtad simulations at the same lattice spacings and quark masses. We also discuss methods for setting the scale, or assigning a lattice spacing to ensembles run at unphysical parameters.

hep-lat↗

arXiv2010

Results for light pseudoscalar mesons

We present the current status of the MILC collaboration's calculations of the properties of the light pseudoscalar meson sector. We use asqtad staggered ensembles with 2+1 dynamical flavors down to $a \approx 0.045$ fm and light quark mass down to 0.05 $m_s$. Here we describe fits to the data using chiral forms from SU(3) chiral perturbation theory, including all staggered taste violations at NLO and the continuum NNLO chiral logarithms. We emphasize issues of convergence of the chiral expansion.

hep-lat↗

arXiv2010

Semileptonic decays of K and D mesons in 2+1 flavor QCD

The experimentally measured rates of the semileptonic decays K -> pi l nu and D -> K(pi) l nu can be combined with lattice calculations of the associated form factors to precisely extract the CKM matrix elements |V_{us}| and |V_{cs(d)}|. We report on the status of form factor calculations with Fermilab charm quarks and staggered light quarks on the 2+1 flavor asqtad staggered MILC ensembles. Analysis of data for the D -> pi l nu form factor provides a nontrivial test of our methods via comparison with CLEO data. We discuss the use of HISQ valence quarks to calculate the K -> pi l nu form factor f_+^{K pi}(0) and describe tests of our method.

hep-lat↗

arXiv2010

B -> D* l nu at zero recoil: an update

We present an update of our calculation of the form factor for B -> D* l nu at zero recoil, with higher statistics and finer lattices. As before, we use the Fermilab action for b and c quarks, the asqtad staggered action for light valence quarks, and the MILC ensembles for gluons and light quarks (Lüscher-Weisz married to 2+1 rooted staggered sea quarks). In this update, we have reduced the total uncertainty on F(1) from 2.6% to 1.7%. At Lattice2010 we presented a still-blinded result, but this writeup includes the unblinded result from the September 2010 CKM workshop.

hep-lat↗

arXiv2010

Staggered chiral perturbation theory in the two-flavor case and SU(2) analysis of the MILC data

In the light pseudoscalar sector, we study rooted staggered chiral perturbation theory in the two-flavor case. The pion mass and decay constant are calculated through NLO for a partially-quenched theory. In the limit where the strange quark mass is large compared to the light quark masses and the taste splittings, we show that the SU(2) staggered chiral theory emerges from the SU(3) staggered chiral theory, as expected. Explicit relations between SU(2) and SU(3) low energy constants and taste-violating parameters are given. A brief summary of updated SU(2) chiral fits to the MILC lattice data is presented.

hep-lat↗

arXiv2010

Scaling studies of QCD with the dynamical HISQ action

We study the lattice spacing dependence, or scaling, of physical quantities using the highly improved staggered quark (HISQ) action introduced by the HPQCD/UKQCD collaboration, comparing our results to similar simulations with the asqtad fermion action. Results are based on calculations with lattice spacings approximately 0.15, 0.12 and 0.09 fm, using four flavors of dynamical HISQ quarks. The strange and charm quark masses are near their physical values, and the light-quark mass is set to 0.2 times the strange-quark mass. We look at the lattice spacing dependence of hadron masses, pseudoscalar meson decay constants, and the topological susceptibility. In addition to the commonly used determination of the lattice spacing through the static quark potential, we examine a determination proposed by the HPQCD collaboration that uses the decay constant of a fictitious "unmixed s bar s" pseudoscalar meson. We find that the lattice artifacts in the HISQ simulations are much smaller than those in the asqtad simulations at the same lattice spacings and quark masses.

hep-lat↗

arXiv2010

QCD thermodynamics with nonzero chemical potential at $N_t=6$ and effects from heavy quarks

We extend our work on QCD thermodynamics with 2+1 quark flavors at nonzero chemical potential to finer lattices with $N_t=6$. We study the equation of state and other thermodynamic quantities, such as quark number densities and susceptibilities, and compare them with our previous results at $N_t=4$. We also calculate the effects of the addition of the charm and bottom quarks on the equation of state at zero and nonzero chemical potential. These effects are important for cosmological studies of the early Universe.

hep-lat↗

arXiv2010

Topological susceptibility with the asqtad action

Chiral perturbation theory predicts that in quantum chromodynamics (QCD), light dynamical quarks suppress the gauge-field topological susceptibility of the vacuum. The degree of suppression depends on quark multiplicity and masses. It provides a strong consistency test for fermion formulations in lattice QCD. Such tests are especially important for staggered fermion formulations that lack a full chiral symmetry and use the "fourth-root" procedure to achieve the desired number of sea quarks. Over the past few years we have measured the topological susceptibility on a large database of 18 gauge field ensembles, generated in the presence of 2+1 flavors of dynamical asqtad quarks with up and down quark masses ranging from 0.05 to 1 in units of the strange quark mass and lattice spacings ranging from 0.045 fm to 0.12 fm. Our study also includes three quenched ensembles with lattice spacings ranging from 0.06 to 0.12 fm. We construct the topological susceptibility from the integrated point-to-point correlator of the discretized topological charge density F-Fdual. To reduce its variance, we model the asymptotic tail of the correlator. The continuum extrapolation of our results for the topological susceptibility agrees nicely at small quark mass with the predictions of lowest-order SU(3) chiral perturbation theory, thus lending support to the validity of the fourth-root procedure.

hep-lat↗

arXiv2009

The Ds and D+ Leptonic Decay Constants from Lattice QCD

We present the leptonic decay constants fDs and fD+ computed on the MILC collaboration's 2+1 flavor asqtad gauge ensembles. We use clover heavy quarks with the Fermilab interpretation and improved staggered light quarks. The simultaneous chiral and continuum extrapolation, which determines both decay constants, includes partially-quenched lattice results at lattice spacings a ~ 0:09, 0:12 and 0:15 fm. We have made several recent improvements in our analysis: a) we include terms in the fit describing leading order heavy-quark discretization effects, b) we have adopted a more precise input r1 value consistent with our other D and B meson studies, c) we have retuned the input bare charm masses based upon the new r1. Our preliminary results are fDs = 260 +/-10 MeV and fD+ = 217 +/-10 MeV.

hep-lat↗

arXiv2009

Progress on charm semileptonic form factors from 2+1 flavor lattice QCD

Lattice calculations of the form factors for the charm semileptonic decays D to K l nu and D to pi l nu provide inputs to direct determinations of the CKM matrix elements |V(cs)| and |V(cd)| and can be designed to validate calculations of the form factors for the bottom semileptonic decays B to pi l nu and B to K l l-bar. We are using Fermilab charm (bottom) quarks and asqtad staggered light quarks on the 2+1 flavor asqtad MILC ensembles to calculate the charm (bottom) form factors. We outline improvements to the previous calculation of the charm form factors and detail our progress. We expect our current round of data production to allow us to reduce the theoretical uncertainties in |V(cs)| and |V(cd)| from 10.5% and 11%, respectively, to about 7%.

hep-lat↗

arXiv2009

Results from the MILC collaboration's SU(3) chiral perturbation theory analysis

We present the status of the MILC collaboration's analysis of the light pseudoscalar meson sector with SU(3) chiral fits. The analysis includes data from new ensembles with smaller lattice spacing, smaller light quark masses and lighter than physical strange quark masses. Our fits include the NNLO chiral logarithms. We present results for decay constants, quark masses, Gasser-Leutwyler low energy constants, and condensates in the two- and three-flavor chiral limits.

hep-lat↗

arXiv2009

Progress on four flavor QCD with the HISQ action

We describe recent progress on generation of gauge configurations using the Highly Improved Staggered Quark (HISQ) action that was designed by the HPQCD/UKQCD collaboration. The HISQ action requires two levels of smearing with a reunitarization of the links before the second smearing. We describe how we deal with the occurrence of occasional large forces arising from the reunitarization step. The MILC collaboration is currently generating ensembles with approximate lattice spacings of 0.15, 0.12, 0.09, and 0.06 fm, with the strange and charm quark masses close to their physical values and the mass of the light quarks m_l set to 0.2 m_s. We present recent results for pion taste splittings, light hadron masses, the static potential, the eta_c dispersion relation and the topological susceptibility.

hep-lat↗

arXiv2009

SU(2) chiral fits to light pseudoscalar masses and decay constants

We present the results of fits to recent asqtad data in the light pseudoscalar sector using SU(2) partially-quenched staggered chiral perturbation theory. Superfine (a~0.06 fm) and ultrafine (a~0.045 fm) ensembles are used, where light sea quark masses and taste splittings are small compared to the strange quark mass. Our fits include continuum NNLO chiral logarithms and analytic terms. We give preliminary results for the pion decay constant, SU(2) low-energy constants and the chiral condensate in the two-flavor chiral limit.

hep-lat↗

arXiv2009

MILC results for light pseudoscalars

We present the latest preliminary results of the MILC collaboration's analysis of the light pseudoscalar meson sector. The analysis includes data from new ensembles with smaller lattice spacings, smaller light quark masses and lighter-than-physical strange quark masses. Both SU(2) and SU(3) chiral fits, including NNLO chiral logarithms, are shown. We give results for decay constants, quark masses, Gasser-Leutwyler low energy constants, and condensates in the two- and three-flavor chiral limits.

hep-ph↗

arXiv2009

QCD equation of state at non-zero chemical potential

We present our new results for the QCD equation of state at nonzero chemical potential at N_t=6 and compare them with N_t=4. We use the Taylor expansion method with terms up to sixth order in simulations with 2+1 flavors of improved asqtad quarks along a line of constant physics with m_l=0.1 m_s and approximately physical strange quark mass m_s.

hep-lat↗