1,027 research outputs found
Isospin Breaking in the Pion-Nucleon Coupling from QCD Sum Rules
We use QCD sum rules for the three point function of a pseudoscalar and two
nucleonic currents in order to estimate the charge dependence of the pion
nucleon coupling constant coming from isospin violation in the
strong interaction. The effect can be attributed primarily to the difference of
the quark condensates . For the splitting
we obtain an interval of to , the uncertainties coming mainly from the input
parameters. The charged pion nucleon coupling is found to be the average of
and . Electromagnetic effects are not included.Comment: 18 pages (REVTeX) + 2 figures (as PostScript), to be published in
PRC, replaced with final version: inclusion of pi-eta mixing and N -> N*
transition
Octet Baryons at Finite Temperature: QCD Sum Rules vs. Chiral Symmetry
Correlators of the octet baryons in the hot pion gas are studied in the
framework of the QCD sum rule. The condensates appearing in the OPE side of the
correlators become T-dependent through the interaction with thermal pions. We
present an explicit demonstration that the -dependence of the
condensates is completely compensated by the change of the pole residue and the
scattering effect in the spectral functions. Therefore
the baryon masses are constant to this order, although
, which
is consistent with the chiral symmetry constraint by Leutwyler and Smilga.Comment: 19 pages, MSUNSCL-870, LaTex files, 2 figs. consisting of simple
Feynmann diagrams not included, Phys.Rev.D in pres
QCD sum rules for the pseudoscalar decay constants - To constrain the strange quark mass
We study the higher order corrections of quark masses to the
Gell-MannOakesRenner (GOR) relation by constructing QCD sum rules
exclusively for pseudoscalar mesons from the axial-vector correlation function,
. To project out
the pseudoscalar meson contributions, we apply to this
correlation function and construct sum rules for the decay constants of
pseudoscalar mesons, and . The OPE is proportional to
quark masses due to PCAC. To leading order in quark mass, each sum rule
reproduces the corresponding GOR relation. For kaon and , the deviation
from the GOR relation due to higher orders in quark mass is found to be
substantial. But the deviation gives better agreements with the phenomenology.
Our sum rule provides a sensitive relation between and , which
stringently constrain the value for . To reproduce the experimental value
for , is found to be 186 MeV at 1 GeV scale. The sum
rule also supports this finding.Comment: 14 pages including 3 figures. slightly revised. Accepted for
publication in Physical Review
Light-Quark Mesons and Four-Quark Condensates at Finite Temperature
We propose an analog of the familiar gap equation for the case of four-quark
condensates at finite temperature. The condensates of interest correspond to
scalar, vector, psudoscalar, axial vector, and tensor Dirac structures. Working
with correlators at zero chemical potential without factorization, we arrive at
coupled equations for these four-quark condensates and the masses of certain
light-quark mesons. We study the temperature dependence of the four-quark
condensates and masses; in one of our models, factorization of the four-quark
condensates is shown to be increasingly violated as the temperature is
increased toward . The 2 tensor mesons a(1320)-f(1270) are
identified as especially sensitive probes of the four-quark condensates.Comment: Latex file, 6 Fig
Spectral asymmetries in nucleon sum rules at finite density
Apparent inconsistencies between different formulations of nucleon sum rules
at finite density are resolved through a proper accounting of asymmetries in
the spectral functions between positive- and negative-energy states.Comment: 10 pages in RevTeX, OSU-090
Quark condensate in nuclear matter based on Nuclear Schwinger-Dyson formalism
The effects of higher order corrections of ring diagrams for the quark
condensate are studied by using the bare vertex Nuclear Schwinger Dyson
formalism based on - model. At the high density the quark
condensate is reduced by the higher order contribution of ring diagrams more
than the mean field theory or the Hartree-Fock
The Goldberger-Treiman Discrepancy
The Golberger- Treiman discrepancy is related to the asymptotic behaviour of
the pionic form factor of the nucleon obtained from baryonic QCD sum rules. The
result is .015<=Delta_{GT}<=.022Comment: References updated and minor correction
Phenomenology of Decays
Using the QCD sum rules technique we study several aspects of the
phenomenology of the b-flavoured strange meson . In particular, we
evaluate the mass of the particle, the leptonic constant and the form factors
of the decays , , . We also calculate, in the factorization approximation, a number of
two-body non leptonic decays.Comment: 19 pages, 2 figures (not included) available upon request, LaTex,
BARI-TH/93-139, UTS-DFT-93-1
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