188 research outputs found
Virtual Photon Correction to the Decay
We consider electromagnetic corrections to the non-leptonic kaon decay,
, due to explicit virtual photons only. The decay
amplitude is calculated at one-loop level in the framework of Chiral
Perturbation Theory. The interest in this process is twofold: It is actually
measured by the NA48 collaboration from one side, and, the value of the
amplitude at the threshold gives access to scattering lengths
from the other side. We found that the present correction is about 5 to 6% the
value of the Born amplitude squared. Combined with another piece published
recently, this fixes the size of isospin breaking correction to the amplitude
squared to 7% its one-loop level value in the absence of isospin breaking and
at the center of Dalitz plot.Comment: 29 pages, 1 LaTeX file, 1 pdf file including all 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
Supersymmetry breaking as the origin of flavor
We present an effective flavor model for the radiative generation of fermion
masses and mixings based on a SU(5)xU(2) symmetry. We assume that the original
source of flavor breaking resides in the supersymmetry breaking sector. Flavor
violation is transmitted radiatively to the fermion Yukawa couplings at low
energy through finite supersymmetric threshold corrections. This model can fit
the fermion mass ratios and CKM matrix elements, explain the non-observation of
proton decay, and overcome present constraints on flavor changing processes
through an approximate radiative alignment between the Yukawa and the soft
trilinear sector. The model predicts new relations between dimensionless
fermion mass ratios in the three fermion sectors, and the quark mixing angles.Comment: 14 pages, RevTex
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
Measuring the a0-a2 pion scattering lengths through decays
We discuss the recent Cabibbo's proposal to measure the pion-pion scattering lengths combination a0-a2 from the cusp effect in the pi0-pi0 energy spectrum at threshold for K+ to (pi0 pi0 pi+) and KL to (pi0 pi0 pi0). We estimate the theoretical uncertainty of the a0-a2 determination at NLO in our approach and obtain that it is not smaller than 5% for K+ to (pi0 pi0 pi+). One gets similar theoretical uncertainties if the neutral KL to (pi0 pi0 pi0) decay data below threshold are used instead. For this decay, there are very large theoretical uncertainties above threshold due to cancellations and data above threshold cannot be used to get the scattering lengths
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