15,071 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
On p_T-broadening of high energy partons associated with the LPM effect in a finite-volume QCD medium
We study the contributions from radiation to -broadening of a high
energy parton traversing a QCD medium with a finite length . The interaction
between the parton and the medium is described by decorrelated static multiple
scattering. Amplitudes of medium-induced gluon emission and parton self-energy
diagrams are evaluated in the soft gluon limit in the BDMPS formalism. We find
both the double-logarithmic correction from incoherent scattering, which is
parametrically the same as that in single scattering, and the logarithmic
correction from the LPM effect. Therefore, we expect a parametrically large
correction from radiation to the medium-induced -broadening in
perturbative QCD.Comment: 19 pages, focusing only on calculations about the medium-induced
diagrams, origin for double-log reinterpreted, final version to appear in
JHE
SPH simulations of the chemical evolution of bulges
We have implemented a chemical evolution model on the parallel AP3M+SPH DEVA
code which we use to perform high resolution simulations of spiral galaxy
formation. It includes feedback by SNII and SNIa using the Qij matrix
formalism. We also include a diffusion mechanism that spreads newly introduced
metals. The gas cooling rate depends on its specific composition. We study the
stellar populations of the resulting bulges finding a potential scenario where
they seem to be composed of two populations: an old, metal poor,
-enriched population, formed in a multiclump scenario at the beginning
of the simulation and a younger one, formed by slow accretion of satellites or
gas, possibly from the disk due to instabilities.Comment: 2 pages, 3 figures. Proceedings of IAUS 245 "Formation and Evolution
of Galaxy Bulges
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