The Mixed-Isospin Vector Current Correlator in Chiral Perturbation Theory and QCD Sum Rules

The mixed-isospin vector current correlator, $\langle 0\vert T(V^\rho_\mu V^\omega_\nu )\vert 0\rangle$ 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 $q^2=0$, by the most nearby singularities. Inclusion of contributions associated with the $\phi$ meson rectify this problem. The resulting sum rule fit provides evidence for a significant direct $\omega\rightarrow\pi\pi$ coupling contribution in $e^+e^-\rightarrow\pi^+\pi^-$. It is also pointed out that results for the $q^2$-dependence of the correlator cannot be used to provide information about the (off-shell) $q^2$-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 $q^2=0$ 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

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

alpha_s From the Lattice and Hadronic Tau Decays

Until recently, determinations of alpha_s(M_Z) from hadronic tau decays and the analysis of short-distance-sensitive lattice observables yielded results which, though precise, were not in good agreement. I review new analyses that bring these into good agreement and provide some details on the source of the main changes in the tau decay analysis.Comment: 4 pages, prepared for the proceedings of CIPANP 09, San Diego, USA, March 26-31, 200

Pion mass dependence of the HVP contribution to muon g−2g-2

One of the systematic errors in some of the current lattice computations of the HVP contribution to the muon anomalous magnetic moment $g-2$ is that associated with the extrapolation to the physical pion mass. We investigate this extrapolation assuming lattice pion masses in the range of 220 to 440 MeV with the help of two-loop chiral perturbation theory, and find that such an extrapolation is unlikely to lead to control of this systematic error at the 1% level. This remains true even if various proposed tricks to improve the chiral extrapolation are taken into account.Comment: 8 pages, 3 figures; contribution to the proceedings of Lattice 201