55,075 research outputs found
Vector Meson Dominance and at Finite Temperature from QCD Sum Rules
A Finite Energy QCD sum rule at non-zero temperature is used to determine the
- and the T-dependence of the vertex function in the
space-like region. A comparison with an independent QCD determination of the
electromagnetic pion form factor at indicates that Vector
Meson Dominance holds to a very good approximation at finite temperature. At
the same time, analytical evidence for deconfinement is obtained from the
result that vanishes at the critical temperature
, independently of . Also, by extrapolating the form
factor to , it is found that the pion radius increases with increasing
, and it diverges at .Comment: 7 pages, Latex, 3 figures to be delivered from the authors by
request, to appear in Phys. Lett.
Operator product expansion and duality at finite temperature
The operator product expansion of current correlators at short distances, and
the notion of QCD-hadron duality are the cornerstone of QCD sum rules. The
extension of this programme to is discussed, together with
applications to hot hadronic propagators. Indications are that the hadronic
spectrum suffers a substantial rearrangement with increasing temperature, and
hint on the existence of a quark deconfining phase transition. Phenomenological
order parameters to characterize this phase transition are discussed.Comment: UCT-TP-209/94. Invited talk at QCD-94, Montpellier, July 1994. LATEX
file. 5 pages. NO figure
QCD sum rules and thermal properties of Charmonium in the vector channel
The thermal evolution of the hadronic parameters of charmonium in the vector
channel, i.e. the J/psi resonance mass, coupling (leptonic decay constant),
total width, and continuum threshold is analyzed in the framework of thermal
Hilbert moment QCD sum rules. The continuum threshold , as in other
hadronic channels, decreases with increasing temperature until the PQCD
threshold s_0 = 4, m_Q^2 is reached at T \simeq 1.22T_c (m_Q is the charm quark
mass) and the J/psi mass is essentially constant in a wide range of
temperatures. The other hadronic parameters behave in a very different way from
those of light-light and heavy-light quark systems. The total width grows with
temperature up to T \simeq 1.04T_c beyond which it decreases sharply with
increasing T. The resonance coupling is also initially constant beginning to
increase monotonically around T \simeq T_c. This behavior strongly suggests
that the J/psi resonance might survive beyond the critical temperature for
deconfinement, in agreement with lattice QCD results.Comment: 4 pages, two figures, contribution to QCD 10, Montpellier 28th
June-2nd July 201
Pion form factor in large QCD
The electromagnetic form factor of the pion is obtained using a particular
realization of QCD in the large limit, which sums up the infinite number
of zero-width resonances to yield an Euler's Beta function of the Veneziano
type. This form factor agrees with space-like data much better than single
rho-meson dominance. A simple unitarization ansatz is illustrated, and the
resulting vector spectral function in the time-like region is shown to be in
reasonable agreement with the ALEPH data from threshold up to about 1.3
.Comment: Plain Latex, 9 pages, 2 figure
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
Electromagnetic pion form factor at finite temperature
The electromagnetic form factor of the pion in the space-like region, and at
finite temperature, , is obtained from a QCD Finite Energy
Sum Rule. The form factor decreases with increasing T, and vanishes at some
critical temperature, where the pion radius diverges. This divergence may be
interpreted as a signal for quark deconfinement.Comment: LATEX File. UCT-TP-215/94. One figure available on request. To be
published in Phys. Lett.
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
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 and
, are used to determine the subtraction constants and
, which fix the ratio .
Our results are ,
, and . 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 .Comment: Latex file, 14 pages including 3 figure
Determination of the strange-quark mass from QCD pseudoscalar sum rules
A new determination of the strange-quark mass is discussed, based on the
two-point function involving the axial-vector current divergences. This Green
function is known in perturbative QCD up to order O(alpha_s^3), and up to
dimension-six in the non-perturbative domain. The hadronic spectral function is
parametrized in terms of the kaon pole, followed by its two radial excitations,
and normalized at threshold according to conventional chiral-symmetry. The
result of a Laplace transform QCD sum rule analysis of this two-point function
is: m_s(1 GeV^2) = 155 pm 25 MeV.Comment: Invited talk given by CAD at QCD98, Montpellier, July 1998. To appear
in Nucl.Phys.B Proc.Suppl. Latex File. Four (double column) page
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
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