376 research outputs found
Extracting m_s From Flavor Breaking in Hadronic Tau Decays
New finite energy sum rules (FESR's) for extracting m_s from hadronic tau
decay data are constructed which (1) significantly reduce potential theoretical
uncertainties present in existing sum rule analyses and (2) remove problems
associated with both the poor convergence of the OPE representation of the
longitudinal part of the vector and axial vector correlators and the large
statistical errors in the spectral data above the K^* region.Comment: 4 pages, 1 figure. Report of presentations to International
Conference on Quark Nuclear Physics, Adelaide, Feb. 21-25, 2000, 16th
International Conference on Problems in Few-Body Physics, Taipei, March 6-10,
2000, and 7th Conference on the Intersections of Particle and Nuclear
Physics, Quebec City, May 22-28, 200
Evidence for charm-bottom tetraquarks and the mass dependence of heavy-light tetraquark states from lattice QCD
We continue our study of heavy-light four-quark states and find evidence from
lattice QCD for the existence of a strong-interaction-stable
tetraquark with mass in the range of 15 to 61 MeV below
threshold. Since this range includes the electromagnetic
decay threshold, current uncertainties do not allow us to
determine whether such a state would decay electromagnetically, or only weakly.
We also perform a study at fixed pion mass, with NRQCD for the heavy quarks,
simulating and tetraquarks with or
and variable, unphysical in order to investigate the heavy
mass-dependence of such tetraquark states. We find that the dependence of the
binding energy follows a phenomenologically-expected form and that, though
NRQCD breaks down before is reached, the results at higher
clearly identify the channel as the
most likely to support a strong-interaction-stable tetraquark state at
. This observation serves to motivate the direct
simulation. Throughout we use dynamical ensembles
with pion masses 415, 299, and 164 MeV reaching down almost to the
physical point, a relativistic heavy quark prescription for the charm quark,
and NRQCD for the bottom quark(s).Comment: 24 pages, 4 figure
More on heavy tetraquarks in lattice QCD at almost physical pion mass
We report on our progress in studying exotic, heavy tetraquark states,
. Using publicly available dynamical
Wilson-Clover gauge configurations, generated by the PACS-CS collaboration,
with pion masses 164, 299 and 415 MeV, we extend our previous analysis
to heavy quark components containing heavier than physical bottom quarks or , charm and bottom quarks and also only charm quarks
. Throughout we employ NRQCD and relativistic heavy quarks for
the heavier than bottom, bottom and charm quarks. Using our previously
established diquark-antidiquark and meson-meson operator basis we comment in
particular on the dependence of the binding energy on the mass of the heavy
quark component , with heavy quarks ranging from . In the heavy flavor non-degenerate case, ,
and especially for the tetraquark channel , we extend our work
to utilize a GEVP to study the ground and threshold states thereby
enabling a clear identification of possible binding. Finally, we present
initial work on the system where a much
larger operator basis is available in comparison to flavor combinations with
NRQCD quarks.Comment: 8 pages, 5 figures, proceedings contribution to "Lattice 2017. 35th
International Symposium on Lattice Field Theory", 18th-24th June 2017,
Granada, Spai
Issues in determining alpha_s from hadronic tau decay and electroproduction data
We discuss some key issues associated with duality-violating and
non-perturbative OPE contributions to the theoretical representations of light
quark current-current two-point functions and relevant to precision
determinations of alpha_s from hadronic tau decay and electroproduction
cross-section data. We demonstrate that analyses with an explicit
representation of duality-violating effects are required to bring theoretical
errors in such extractions under control, motivating the accompanying paper in
these proceedings, which presents the results of such an analysis.Comment: 5 pages, 4 figures. Prepared for the Proceedings of the International
Workshop on e+e- collisions from Phi to Psi (PHIPSI11), Sep. 19-22, 2011,
BINP, Novosibirsk, Russi
Isospin-Breaking Vacuum-to-Pi^0,Eta Pseudoscalar Matrix Elements at Next-to-Leading Order in the Chiral Expansion
We employ Chiral Perturbation Theory (ChPT) to evaluate the complete set of
pseudoscalar matrix elements, , with P_f any of the
flavor-diagonal pseudoscalar currents (f=u,d,s), to order (m_d-m_u), and to
next-to-leading order in the chiral expansion. These matrix elements represent
the basic input to a QCD sum rule analysis of isospin breaking in the pi NN
couplings using the three-point-function method. We discuss also how one could
use the results to construct a one parameter family of interpolating fields for
the , all of whose members have zero vacuum-to- matrix element,
and explain how this could in principle be used to provide non-trivial tests of
the reliability of the assumptions underlying the use of the
three-point-function method. It is shown that the isospin-breaking mixing
parameters required for this construction receive significant corrections
beyond leading order in the chiral expansion.Comment: 9 pages, 1 postscript figur
Some continuum physics results from the lattice V-A correlator
We present preliminary results on extractions of the chiral LECs L_10 and
C_87 and constraints on the excited pseudoscalar state pi(1300) and pi(1800)
decay constants obtained from an analysis of lattice data for the flavor ud
light quark V-A correlator. A comparison of the results for the correlator to
the corresponding mildly-model-dependent continuum results (based primarily on
experimental hadronic tau decay data) is also givenComment: 7 pages, 3 figures. Prepared for the Proceedings of the 30th
International Symposium on Lattice Field Theory, Cairns, Australia, June
24-29, 2012; expanded version of Reference 1
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