883 research outputs found
The coupling with relativistic heavy quarks
We report on a calculation of the coupling in lattice QCD. The
strong matrix element is directly related to the
leading order low-energy constant in heavy meson chiral perturbation theory
(HMPT) for -mesons. We carry out our calculation directly at the
-quark mass using a non-perturbatively tuned clover action that controls
discretisation effects of order and for all . Our
analysis is performed on RBC/UKQCD gauge configurations using domain wall
fermions and the Iwasaki gauge action at two lattice spacings of
GeV, GeV, and unitary pion masses down to 290
MeV. We achieve good statistical precision and control all systematic
uncertainties, giving a final result for the HMPT coupling in the continuum and at the physical light-quark
masses. This is the first calculation performed directly at the physical
-quark mass and lies in the region one would expect from carrying out an
interpolation between previous results at the charm mass and at the static
point.Comment: 7 pages, 2 figures, presented at the 31st International Symposium on
Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
Annexin A1 regulates TGF-beta signaling and promotes metastasis formation of basal-like breast cancer cells
Visualization of semileptonic form factors from lattice QCD
Comparisons of lattice-QCD calculations of semileptonic form factors with
experimental measurements often display two sets of points, one each for
lattice QCD and experiment. Here we propose to display the output of a
lattice-QCD analysis as a curve and error band. This is justified, because
lattice-QCD results rely in part on fitting, both for the chiral extrapolation
and to extend lattice-QCD data over the full physically allowed kinematic
domain. To display an error band, correlations in the fit parameters must be
taken into account. For the statistical error, the correlation comes from the
fit. To illustrate how to address correlations in the systematic errors, we use
the Becirevic-Kaidalov parametrization of the D -> pi l nu and D -> K l nu form
factors, and a analyticity-based fit for the B -> pi l nu form factor f_+.Comment: 6 pp; v2 conforms with published version (one additional sentence and
reference to clarify a point
Short-distance matrix elements for D0-meson mixing from Nf=2+1 lattice QCD
We calculate in three-flavor lattice QCD the short-distance hadronic matrix elements of all five ΔC=2 four-fermion operators that contribute to neutral
D-meson mixing both in and beyond the Standard Model. We use the MILC Collaboration’s Nf=2+1 lattice gauge-field configurations generated with asqtad-improved staggered sea quarks. We also employ the asqtad action for the valence light quarks and use the clover action with the Fermilab interpretation for the charm quark. We analyze a large set of ensembles with pions as light as lattice gauge-field configurations generated with asqtad-improved staggered sea quarks. We also employ the asqtad action for the valence light quarks and use the clover action with the Fermilab interpretation for the charm quark. We analyze a large set of ensembles with pions as light as Mπ ≈ 180 MeV and lattice spacings as fine as a ≈ 0.045 fm, thereby enabling good control over the extrapolation to the physical pion mass and continuum limit. We obtain for the matrix elements in the MS−NDR scheme using the choice of evanescent operators proposed by Beneke et al., evaluated at 3 GeV, ⟨D0|Oi|¯D0⟩ = {0.0805(55)16),−0.1561(70)(31), 0.0464(31)(9), 0.2747(129)(55), 0.1035(71)(21)} GeV4 (i=1–5). The errors shown are from statistics and lattice systematics, and the omission of charmed sea quarks, respectively. To illustrate the utility of our matrix-element results, we place bounds on the scale of CP-violating new physics in D0 mixing, finding lower limits of about 10–50×103 TeV for couplings of O(1). To enable our results to be employed in more sophisticated or model-specific phenomenological studies, we provide the correlations among our matrix-element results. For convenience, we also present numerical results in the other commonly used scheme of Buras, Misiak, and Urban
The OscSNS White Paper
There exists a need to address and resolve the growing evidence for
short-baseline neutrino oscillations and the possible existence of sterile
neutrinos. Such non-standard particles require a mass of eV/c, far
above the mass scale associated with active neutrinos, and were first invoked
to explain the LSND appearance signal.
More recently, the MiniBooNE experiment has reported a excess of
events in antineutrino mode consistent with neutrino oscillations and with the
LSND antineutrino appearance signal. MiniBooNE also observed a
excess of events in their neutrino mode data. Lower than expected
neutrino-induced event rates using calibrated radioactive sources and nuclear
reactors can also be explained by the existence of sterile neutrinos. Fits to
the world's neutrino and antineutrino data are consistent with sterile
neutrinos at this eV/c mass scale, although there is some tension
between measurements from disappearance and appearance experiments. In addition
to resolving this potential major extension of the Standard Model, the
existence of sterile neutrinos will impact design and planning for all future
neutrino experiments. It should be an extremely high priority to conclusively
establish if such unexpected light sterile neutrinos exist. The Spallation
Neutron Source (SNS) at Oak Ridge National Laboratory, built to usher in a new
era in neutron research, provides a unique opportunity for US science to
perform a definitive world-class search for sterile neutrinos.Comment: This white paper is submitted as part of the SNOWMASS planning
proces
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