Tau Decay Determination of the Strange Quark Mass

The recent ALEPH measurements of the inclusive Cabibbo--suppressed decay width of the $\tau$ and several moments of its invariant mass distribution are used to determine the value of the strange quark mass. We obtain, in the $\bar{\rm MS}$ scheme, $m_s(M_\tau^2) = (119\pm 24)$ MeV, which corresponds to $m_s(1 {\rm GeV}^2) = (164 \pm 33) {\rm MeV}, m_s(4 {\rm GeV}^2) = (114\pm 23) {\rm MeV}$.Comment: 5pages. Invited talk at QCD'99 (Montpellier, July 1999

Chiral low-energy constants from tau data

We analyze how the recent precise hadronic tau-decay data on the V-A spectral function and general properties of QCD such as analyticity, the operator product expansion and chiral perturbation theory (ChPT), can be used to improve the knowledge of some of the low-energy constants of ChPT. In particular we find the most precise values of L_{9,10} (or equivalently l_{5,6}) at order p^4 and p^6 and the first phenomenological determination of C_87 (c_50).Comment: Proceedings of the 6th International Workshop on Chiral Dynamics (Bern, Switzerland, July 6-10, 2009). 9 pages, 3 figure

The Hadronic Light-by-Light Contribution to the Muon Anomalous Magnetic Moment: Where do we stand?

We review the status of the hadronic light-by-light contribution to the muon anomalous magnetic moment and critically compare recent calculations. We also study in detail which momentum regions the pi^0 exchange main contribution originates. We also argue that a_\mu^{light-by-light} = (11 \pm 4) \times 10^{-10} encompasses the present understanding of this contribution and comment on some directions to improve on that.Comment: 16 pages, 9 figure

Yukawa coupling and anomalous magnetic moment of the muon: an update for the LHC era

We study the interplay between a soft muon Yukawa coupling generated radiatively with the trilinear A-terms of the minimal supersymmetric standard model (MSSM) and the anomalous magnetic moment of the muon. In the absence of a tree-level muon Yukawa coupling the lightest smuon mass is predicted to be in the range between 750 GeV and 2700 GeV at 2 sigma, if the bino mass M_1 is below 1 TeV. Therefore, a detection of a smuon (in conjunction with a sub-TeV bino) at the LHC would directly imply a non-zero muon Yukawa coupling in the MSSM superpotential. Inclusion of slepton flavor mixing could in principle lower the mass of one smuon-like slepton below 750 GeV. However, the experimental bounds on radiative lepton decays instead strengthen the lower mass bound, with larger effects for smaller M_1, We also extend the analysis to the electron case and find that a light selectron close to the current experimental search limit may prove the MSSM electron Yukawa coupling to be non-zero.Comment: 6 pages, 2 figures, references added, version accepted for publication in PR

High Efficiency Positron Accumulation for High-Precision Measurements

Positrons are accumulated within a Penning trap designed to make more precise measurements of the positron and electron magnetic moments. The retractable radioactive source used is weak enough to require no license for handling radioactive material and the radiation dosage one meter from the source gives an exposure several times smaller than the average radiation dose on the earth's surface. The 100 mK trap is mechanically aligned with the 4.2 K superconducting solenoid that produces a 6 tesla magnetic trapping field with a direct mechanical coupling.Comment: 7 pages, 9 figure

Determination of |V_us| from hadronic tau decays

The recent update of the strange spectral function and the moments of the invariant mass distribution by the OPAL collaboration from hadronic tau decay data are employed to determine |V_us| as well as m_s. Our result, |V_us|=0.2208\pm0.0034, is competitive to the standard extraction of |V_us| from K_e3 decays and to the new proposals to determine it. Furthermore, the error associated to our determination of |V_us| can be reduced in the future since it is dominated by the experimental uncertainty that will be eventually much improved by the B-factories hadronic tau data. Another improvement that can be performed is the simultaneous fit of both |V_us| and m_s to a set of moments of the hadronic tau decays invariant mass distribution, which will provide even a more accurate determination of both parameters.Comment: 6 pages. Invited talk given by E.G. at the XXXXth Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy, 5-12 Mar 200

Measuring the muon's anomalous magnetic moment to 0.14 ppm

The anomalous magnetic moment (g-2) of the muon was measured with a precision of 0.54 ppm in Experiment 821 at Brookhaven National Laboratory. A difference of 3.2 standard deviations between this experimental value and the prediction of the Standard Model has persisted since 2004; in spite of considerable experimental and theoretical effort, there is no consistent explanation for this difference. This comparison hints at physics beyond the Standard Model, but it also imposes strong constraints on those possibilities, which include supersymmetry and extra dimensions. The collaboration is preparing to relocate the experiment to Fermilab to continue towards a proposed precision of 0.14 ppm. This will require 20 times more recorded decays than in the previous measurement, with corresponding improvements in the systematic uncertainties. We describe the theoretical developments and the experimental upgrades that provide a compelling motivation for the new measurement.Comment: 5 pages, 1 figure, presented at International Nuclear Physics Conference 2010 (INPC 2010