Virtual Photon Correction to the K+→π+π0π0K^+\to\pi^+\pi^0\pi^0 Decay

We consider electromagnetic corrections to the non-leptonic kaon decay, $K^+\to\pi^+\pi^0\pi^0$, 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 $\pi\pi$ threshold gives access to $\pi\pi$ 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

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 K→3πK \to 3 \pi 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

Dynamical determination of B_K from improved staggered quarks

The scaling corrections that affected previous staggered calculations of B_K have been proved to be reduced by using improved actions (HYP, Asqtad) in the quenched approximation. This improved behaviour allows us to perform a reliable dynamical calculation of B_K including quark vacuum polarization effects using the MILC (2+1) flavour dynamical configurations. We report here on the results from such dynamical calculation. We also discuss the renormalization effects with the Asqtad action.Comment: 6 pages, 2 figures. Talk presented at Lattice 2005 (Dublin). To appear in Proceedings of Scienc