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 $us$ vector and axial vector correlators and the large statistical errors in the $us$ 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

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

Isospin Breaking in the Extraction of Isovector and Isoscalar Spectral Functions from e^+e^- --> hadrons

A finite energy sum rule (FESR) analysis of the isospin-breaking vector current correlator is used to determine the isospin-breaking electromagnetic (EM) decay constants of the low-lying vector mesons. These results are used to evaluate the corrections required to extract the flavor diagonal 33 and 88 resonance contributions from the full resonance EM contributions to the EM spectral function. A large (~15%) correction is found in the case of the omega contribution to the isoscalar spectral function. The implications of these results for sum rules based on the isovector-isoscalar spectral difference are considered.Comment: Presentation to the 3rd International Conference on Symmetries in Subatomic Physics, Adelaide, Mar. 13-17, 200

Strong Isospin Breaking in CP-even and CP-odd K -> pi pi Decays

Complete next-to-leading (chiral) order (NLO) expressions for the strong isospin-breaking (IB) contributions in K -> pi pi are used to discuss (1) for CP-even, the impact on the magnitude of the Delta I=1/2 Rule, and (2) for CP-odd, the strong IB correction, Omega_st, for the gluonic penguin contribution to epsilon'/epsilon, with particular emphasis on the strong low-energy constant (LEC) and loop contributions, numerical values for which are model-independent at NLO.Comment: 4 pages. Contribution to the proceedings of the 7th Conference on the Intersections of Particle and Nuclear Physics (CIPANP), May 22-28 2000, Quebec City, Canada. Uses AIP 6x9 LaTeX styl

Violation of the Δ\DeltaI=1/2 rule in the nonmesonic weak decay of Λ\Lambda hypernuclei

Violations of the $\Delta$I=1/2 rule are investigated in the nonmesonic weak hypernuclear decay using a weak $\Lambda$N$\to$NN transition potential based on meson exchange. While the weak $\Delta$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.

Constraints on Hadronic Spectral Functions From Continuous Families of Finite Energy Sum Rules

Hadronic tau decay data is used to study the reliability of various finite energy sum rules (FESR's). For intermediate scales (of order 2-3 GeV^2), those FESR's with weights s^k are found to have significant errors, whereas those with weights having a zero at the juncture (s=s_0) of the cut and circular part of the contour work very well. It is also shown that a combination of two such sum rules allows rather strong constraints to be placed on the hadronic spectral function without sacrificing the excellent agreement between OPE and hadronic representations. The method then is applied to the strangeness -1 and pseudoscalar isovector channels, where it is shown to provide novel constraints on those ansatze for the unmeasured continuum parts of the spectral functions employed in existing extractions of m_u+m_d, m_s. The continuum ansätz in the latter channel, in particular, is shown to produce a rather poor match to the corresponding OPE representation, hence re-opening the question of the value of the light quark mass combination m_u+m_d

O(m_d-m_u) Effects in CP-even and CP-odd K-->pi pi Decays

Strong isospin-breaking (IB) effects in CP-even and CP-odd K-->pi pi decays are computed to next-to-leading order (NLO) in the chiral expansion. The impact of these corrections on the magnitude of the Delta I=1/2 Rule and on the size of the IB correction, Omega_IB, to the gluonic penguin contribution to epsilon'/epsilon are discussed