1,018 research outputs found
The Mixed-Isospin Vector Current Correlator in Chiral Perturbation Theory and QCD Sum Rules
The mixed-isospin vector current correlator, is evaluated using both QCD sum rules and Chiral
Perturbation Theory (ChPT) to one-loop order. The sum rule treatment is a
modification of previous analyses necessitated by the observation that those
analyses produce forms of the correlator that fail to be dominated, near
, by the most nearby singularities. Inclusion of contributions
associated with the meson rectify this problem. The resulting sum rule
fit provides evidence for a significant direct
coupling contribution in . It is also pointed out
that results for the -dependence of the correlator cannot be used to
provide information about the (off-shell) -dependence of the off-diagonal
element of the vector meson propagator unless a very specific choice of
interpolating fields for the vector mesons is made. The results for the value
of the correlator near in ChPT are shown to be more than an order of
magnitude smaller than those extracted from the sum rule analysis and the
reasons why this suggests slow convergence of the chiral series for the
correlator given.Comment: 29 pages, uses REVTEX and epsfig.sty with 6 uuencoded figures. Entire
manuscript available as a ps file at
http://www.physics.adelaide.edu.au/theory/home.html . Also available via
anonymous ftp at ftp://adelphi.adelaide.edu.au/pub/theory/ADP-95-20.T179.p
On the Leading ORder Hadronic Contribution to (g-2)_mu
Sum rule constraints dominated by the independent high-scale input,
alpha_s(M_Z), are shown to be satisfied by I=1 spectral data from hadronic tau
decays, but violated by the pre-2005 electroproduction (EM) cross-section data.
Determinations of the Standard Model (SM) hadronic contribution to (g-2)_mu
incorporating tau decay data are thus favored over those based solely on EM
data, implying a SM prediction for (g-2)_mu in agreement with current
experimental results.Comment: 3 pages, 1 figure; prepared for the proceedings of PANIC'0
Quark Model Perspectives on Pentaquark Exotics
Expectations and predictions for pentaquark exotics based on the quark model
perspective are presented. Recent quark model scenarios, and calculations
performed in different realizations of the quark model approach, up to the end
of March 2004, are also reviewed and discussed.Comment: 12 pages, Invited Talk, Workshop on the Physics of Excited Nucleons
(NSTAR 2004), Grenoble, France, March 24-27, 200
OPE Constraints and the Leading Order Hadronic Contribution to (g-2)_mu
OPE constraints are studied as a means of distinguishing between the versions
of the I=1 vector spectral function extracted from (i) inclusive I=1 hadronic
electroproduction cross-sections and (ii) inclusive I=1 hadronic tau decay
data, with the goal of clarifying expectations for the leading order hadronic
contribution to a_mu = (g-2)_mu /2 in the Standard Model. The constraints are
shown to, at present, favor the tau decay data, and hence a Standard Model
prediction for a_mu compatible with the BNL E821 experimental result. The
relative role of the 2pi and 4pi contributions to the discrepancy between the
integrated electroproduction results and the corresponding OPE constraints is
also investigated, and the significance, in this context, of forthcoming
re-measurements of the e^+e^- --> pi^+ pi^- pi^0 pi^0 cross-sections pointed
out.Comment: 6 pages, 5 figures, prepared for the Proceedings of the 9th
International Workshop on Tau Lepton Physic
Violation of the I=1/2 rule in the nonmesonic weak decay of hypernuclei
Violations of the I=1/2 rule are investigated in the nonmesonic weak
hypernuclear decay using a weak NNN transition potential based on
meson exchange. While the weak I=3/2 matrix elements of baryons with
pseudoscalar mesons are known to be very small, the same matrix elements of
baryons with vector mesons, evaluated in the factorization approximation, are
found to be significant. Within the uncertainties of the factorization
approximation we find that the total rate increases by at most 6% lying within
the error bars of the more recent experimental result. The neutron- to
proton-induced rate, on the other hand, can change by up to a factor of two,
while the asymmetry parameter is strongly affected as well.Comment: 17 pages. Paper related to a contribution presented at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97). Submitted to Phys. Lett.
Scalar Meson Decay Constants and the Nature of the a_0(980)
The a_0(980), a_0(1450) and K_0(1430) decay constants are determined using a
form of QCD sum rules known to produce a very accurate determination of the rho
decay constant. The ratio of a_0(980) to K_0(1430) decay constants is shown to
be ~0.6, ruling out both the ``loosely-bound-K\bar{K}-molecule'' and Gribov
minion scenarios for the a_0(980). Solutions for the isovector scalar spectral
function obtained in the literature from sum rule analyses employing a more
restrictive single-resonance-plus-continuum form of the input spectral ansatz,
are also investigated. These solutions, which suggest, in contrast to the
present results, negligible coupling of the a_0(980) to the isovector scalar
density are shown to produce a poor quality match between the OPE and hadronic
sides of the sum rules employed here, and hence to be strongly disfavored
relative to the present solution.Comment: Presented to the International Conference on Quark Nuclear Physics,
Adelaide, Feb. 21-25, 200
Light quark masses: a status report at DPF 2000
A summary of the extraction of light quark masses from both QCD sumrules and
lattice QCD simulations is presented. The focus is on providing a careful
statement of the potential weaknesses in each calculation, and on integrating
the work of different collaborations to provide a coherent picture.Comment: 9 page
Extracting m_s From Flavor Breaking in Hadronic Tau Decays
New finite energy sum rules (FESR's) for extracting m_s from hadronic tau
decay data are constructed which (1) significantly reduce potential theoretical
uncertainties present in existing sum rule analyses and (2) remove problems
associated with both the poor convergence of the OPE representation of the
longitudinal part of the vector and axial vector correlators and the large
statistical errors in the spectral data above the K^* region.Comment: 4 pages, 1 figure. Report of presentations to International
Conference on Quark Nuclear Physics, Adelaide, Feb. 21-25, 2000, 16th
International Conference on Problems in Few-Body Physics, Taipei, March 6-10,
2000, and 7th Conference on the Intersections of Particle and Nuclear
Physics, Quebec City, May 22-28, 200
Some New Results on the H Dibaryon in the Quark Cluster Model
The H dibaryon channel, (I=0,J=0,S=-2), is revisited in the non-relativistic
quark cluster model (NRQCM) using a basis extended beyond the usual set of
baryon cluster pairs to include an explicit spatially symmetric 6q state,
analogous in structure to the MIT bag model H. We find that the binding
predicted using the two-baryon basis alone is significantly deepened by the
addition of the additional 6q configuration. The NRQCM thus appears, contrary
to earlier findings, to be incompatible with the experimental information
available for this channel.Comment: 11 pages, REVTE
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