1,731 research outputs found
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
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
Stop as a next-to-lightest supersymmetric particle in constrained MSSM
So far the squarks have not been detected at the LHC indicating that they are
heavier than a few hundred GeVs, if they exist. The lighter stop can be
considerably lighter than the other squarks. We study the possibility that a
supersymmetric partner of the top quark, stop, is the next-to-lightest
supersymmetric particle in the constrained supersymmetric standard model.
Various constraints, on top of the mass limits, are taken into an account, and
the allowed parameter space for this scenario is determined. Observing stop
which is the next-to-lightest supersymmetric particle at the LHC may be
difficult.Comment: v2: A few references, a plot indicating used parameters, discussion
about the role of parameters in determination of the stop NLSP, CCB minima
and a comment about (g-2) added. Typos corrected. Version in PR
Behavior of propagating and evanescent components in azimuthally polarized non-paraxial fields
The contribution of the propagating and the evanescent waves associated with freely propagating non-paraxial light fields whose transverse component is azimuthally polarized at some plane is investigated. Analytic expressions are derived for describing both the spatial shape and the relative weight of the propagating and the evanescent components integrated over the transverse plane. The analysis is carried out within the framework of the plane-wave angular spectrum approach. These results are used to illustrate the behavior of a kind of donut-like beams with transverse azimuthal polarization at some plane
Strange Quark Mass from the Invariant Mass Distribution of Cabibbo-Suppressed Tau Decays
Quark mass corrections to the tau hadronic width play a significant role only
for the strange quark, hence providing a method for determining its mass. The
experimental input is the vector plus axial-vector strange spectral function
derived from a complete study of tau decays into strange hadronic final states
performed by ALEPH. New results on strange decay modes from other experiments
are also incorporated. The present analysis determines the strange quark mass
at the Mtau mass scale using moments of the spectral function. Justified
theoretical constraints are applied to the nonperturbative components and
careful attention is paid to the treatment of the perturbative expansions of
the moments which exhibit convergence problems. The result obtained,
m_s(Mtau^2) = (120 +- 11_exp +- 8_Vus +- 19_th) MeV = (120^+21_-26) MeV, is
stable over the scale from Mtau down to about 1.4 GeV. Evolving this result to
customary scales yields m_s(1 GeV^2) = (160^+28_-35) MeV and m_s(4 GeV^2) =
(116^+20_-25) MeV.Comment: LaTex, 8 pages, 4 figures (EPS
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