28,997 research outputs found
Couplings between pion and charmed mesons
We compute the couplings ,,,
using QCD sum rules. These couplings are important inputs in the meson exchange
model calculations used to estimate the amount of absorption due to
pions and rho mesons in heavy ion collisions. Our sum rules are constructed at
the first order in the pion momentum , which give the couplings that are
not trivially related to the soft-pion theorem. Our calculated couplings, which
somewhat depend upon the values of the heavy meson decay constants, are
, , and .Comment: 16 pages including 4 postscript figures. To be published in European
Physical Journal
Renormalization of dimension 6 gluon operators
We identify the independent dimension 6 twist 4 gluon operators and calculate
their renormalization in the pure gauge theory. By constructing the
renormalization group invariant combinations, we find the scale invariant
condensates that can be estimated in nonperturbative calculations and used in
QCD sum rules for heavy quark systems in medium.Comment: 4 pages, 2 figure
QCD Sum Rule for S_{11}(1535)
We propose a new interpolating field for S(1535) to determine its mass
from QCD sum rules. In the nonrelativistic limit, this interpolating field
dominantly reduces to two quarks in the s-wave state and one quark in the
p-wave state. An optimization procedure, which makes use of a duality relation,
yields the interpolating field which overlaps strongly with the negative-parity
baryon and at the same time does not couple at all to the low lying
positive-parity baryon. Using this interpolating field and applying the
conventional QCD sum rule analysis, we find that the mass of S is
reasonably close to the experimentally known value, even though the precise
determination depends on the poorly known quark-gluon condensate. Hence our
interpolating field can be used to investigate the spectral properties of
S(1535).Comment: 12 pages, Revtex, 1 ps figure available from author
Light vector correlator in medium: Wilson coefficients up to dimension 6 operators
As an improvement of the QCD sum rule method to study modifications of light
vector mesons in nuclear matter and/or at finite temperature, we calculate the
Wilson coefficients of all independent gluonic non-scalar operators up to
dimension 6 in the operator product expansion (OPE) of the vector channel for
light quarks. To obtain the gluon part of the light quark OPE from the heavy
quark one, we also compute the heavy quark expansion of the relevant quark
condensates. Together with the results for the quark operators that are already
available in the literature, this completes the OPE of the vector channel in a
hot or dense medium for operators up to dimension 6.Comment: 6 pages, no figur
Proper construction of the continuum in light-cone QCD sum rules
A proper way of subtracting the continuum contributions in light-cone QCD sum
rules (LCQSR) is demonstrated. Specifically, we calculate the continuum
corresponding to a typical OPE appearing in LCQSR by properly combining the
double dispersion relation with QCD duality. We demonstrate how the subtraction
terms can spuriously contribute to the sum rules. In the limit of zero external
momentum, taking out the spurious continuum is found to yield the sum rules
using the single-variable dispersion relation. The continuum factor constructed
in this way differs from the one appearing in usual LCQSR. The difference
substantially affects the extraction of hadronic parameters from the
correlation function involving baryon currents.Comment: 12 pages including 3 figures, substantially revised, version to be
published in Progress of Theoretical Physic
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