19,239 research outputs found
Quark masses in QCD: a progress report
Recent progress on QCD sum rule determinations of the light and heavy quark
masses is reported. In the light quark sector a major breakthrough has been
made recently in connection with the historical systematic uncertainties due to
a lack of experimental information on the pseudoscalar resonance spectral
functions. It is now possible to suppress this contribution to the 1% level by
using suitable integration kernels in Finite Energy QCD sum rules. This allows
to determine the up-, down-, and strange-quark masses with an unprecedented
precision of some 8-10%. Further reduction of this uncertainty will be possible
with improved accuracy in the strong coupling, now the main source of error. In
the heavy quark sector, the availability of experimental data in the vector
channel, and the use of suitable multipurpose integration kernels allows to
increase the accuracy of the charm- and bottom-quarks masses to the 1% level.Comment: Invited review paper to be published in Modern Physics Letters
Corrections to the Gell-Mann-Oakes-Renner relation and chiral couplings and
Next to leading order corrections to the
Gell-Mann-Oakes-Renner relation (GMOR) are obtained using weighted QCD Finite
Energy Sum Rules (FESR) involving the pseudoscalar current correlator. Two
types of integration kernels in the FESR are used to suppress the contribution
of the kaon radial excitations to the hadronic spectral function, one with
local and the other with global constraints. The result for the pseudoscalar
current correlator at zero momentum is , leading to the chiral corrections to GMOR: . The resulting uncertainties are mostly due to variations in the upper
limit of integration in the FESR, within the stability regions, and to a much
lesser extent due to the uncertainties in the strong coupling and the strange
quark mass. Higher order quark mass corrections, vacuum condensates, and the
hadronic resonance sector play a negligible role in this determination. These
results confirm an independent determination from chiral perturbation theory
giving also very large corrections, i.e. roughly an order of magnitude larger
than the corresponding corrections in chiral . Combining
these results with our previous determination of the corrections to GMOR in
chiral , , we are able to determine two low
energy constants of chiral perturbation theory, i.e. , and , both at the
scale of the -meson mass.Comment: Revised version with minor correction
QCD determination of the axial-vector coupling of the nucleon at finite temperature
A thermal QCD Finite Energy Sum Rule (FESR) is used to obtain the temperature
dependence of the axial-vector coupling of the nucleon, . We find
that is essentially independent of , in the very wide range , where is the critical temperature. While
at T=0 is -independent, it develops a dependence at
finite temperature. We then obtain the mean square radius associated with
and find that it diverges at , thus signalling quark
deconfinement. As a byproduct, we study the temperature dependence of the
Goldberger-Treiman relation.Comment: 8 pages and 3 figure
Introduction to QCD sum rules
A general, and very basic introduction to QCD sum rules is presented, with
emphasis on recent issues to be described at length in other papers in this
volume of Modern Physics Letters A. Collectively, these papers constitute the
proceedings of the {\it{International Workshop on Determination of the
Fundamental Parameters of QCD}}, Singapore, March 2013.Comment: Plenary talk at the International Workshop on Determination of the
Fundamental Parameters of QCD. To be published in Mod. Phys. Lett.
Deconfinement and Chiral-Symmetry Restoration in Finite Temperature QCD
QCD sum rules are based on the Operator Product Expansion of current
correlators, and on QCD-hadron duality. An extension of this program to finite
temperature is discussed. This allows for a study of deconfinement and
chiral-symmetry restoration. In addition, it is possible to relate certain
hadronic matrix elements to expectation values of quark and gluon field
operators by using thermal Finite Energy Sum Rules. In this way one can
determine the temperature behaviour of hadron masses and couplings, as well as
form factors. An attempt is made to clarify some misconceptions in the existing
literature on QCD sum rules at finite temperature.Comment: Invited talk at CAM-94, Cancun, Mexico, September 1994. 21 pages and
8 figures (not included). LATEX file. UCT-TP-218/9
Electromagnetic Form Factors of Hadrons in Dual-Large QCD
In this talk, results are presented of determinations of electromagnetic form
factors of hadrons (pion, proton, and ) in the framework of
Dual-Large QCD (Dual-). This framework improves considerably
tree-level VMD results by incorporating an infinite number of zero-width
resonances, with masses and couplings fixed by the dual-resonance
(Veneziano-type) model.Comment: Invited talk at the XII Mexican Workshop on Particles & Fields,
Mazatlan, November 2009. To be published in American Institute of Physics
Conference Proceedings Serie
- …