21,731 research outputs found

### The exact renormalization group in Astrophysics

The coarse-graining operation in hydrodynamics is equivalent to a change of
scale which can be formalized as a renormalization group transformation. In
particular, its application to the probability distribution of a
self-gravitating fluid yields an "exact renormalization group equation" of
Fokker-Planck type. Since the time evolution of that distribution can also be
described by a Fokker-Planck equation, we propose a connection between both
equations, that is, a connection between scale and time evolution. We finally
remark on the essentially non-perturbative nature of astrophysical problems,
which suggests that the exact renormalization group is the adequate tool for
them.Comment: World Scientific style, 6 pages, presented at the 2nd Conference on
the Exact RG, Rome 200

### 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

### 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 $N_c$ QCD

In this talk, results are presented of determinations of electromagnetic form
factors of hadrons (pion, proton, and $\Delta(1236)$) in the framework of
Dual-Large $N_c$ QCD (Dual-$QCD_\infty$). 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

### 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.

### Ratio of strange to non-strange quark condensates in QCD

Laplace transform QCD sum rules for two-point functions related to the
strangeness-changing scalar and pseudoscalar Green's functions $\psi(Q^2)$ and
$\psi_5(Q^2)$, are used to determine the subtraction constants $\psi(0)$ and
$\psi_5(0)$, which fix the ratio $R_{su}\equiv \frac{}{}$.
Our results are $\psi(0)= - (1.06 \pm 0.21) \times 10^{-3} {GeV}^4$,
$\psi_5(0)= (3.35 \pm 0.25) \times 10^{-3} {GeV}^4$, and $R_{su}\equiv
\frac{}{} = 0.5 \pm 0.1$. This implies corrections to
kaon-PCAC at the level of 50%, which although large, are not inconsistent with
the size of the corrections to Goldberger-Treiman relations in $SU(3)\otimes
SU(3)$.Comment: Latex file, 14 pages including 3 figure

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