Emilie Passemar

Kμ3L decay: A stringent test of right-handed quark currents

Abstract Clean tests of a small admixture of right-handed quark currents directly coupled to the standard W are still lacking. We show that such non-standard couplings can be significantly constrained measuring the value of the scalar Kπ form factor at the Callan–Treiman point to a few percent. A realistic prospect of such a measurement in K μ 3 L decay based on an accurate dispersive representation of the scalar form factor is presented. The inadequacy of the currently used linear parametrization is explained and illustrated using recent KTeV data. We briefly comment on the charged kaon mode.

Dispersive analysis of KLμ3 and KLe3 scalar and vector form factors using KTeV data

Using the published KTeV samples of K{sub L} {yields} {pi}{sup {+-}}e{sup {-+}}{nu} and K{sub L} {yields} {pi}{sup {+-}}{mu}{sup {-+}}{nu} decays, we perform a reanalysis of the scalar and vector form factors based on the dispersive parameterization. We obtain phase space integrals I{sub K}{sup e} = 0.15446 {+-} 0.00025 and I{sub K}{sup {mu}} = 0.10219 {+-} 0.00025. For the scalar form factor parameterization, the only free parameter is the normalized form factor value at the Callan-Treiman point (C); our best fit results in ln C = 0.1915 {+-} 0.0122. We also study the sensitivity of C to different parametrizations of the vector form factor. The results for the phase space integrals and C are then used to make tests of the Standard Model. Finally, we compare our results with lattice QCD calculations of F{sub K}/F{sub {pi}} and f{sub +}(0).

Model-discriminating power of lepton flavor violating

Within an effective field theory framework, we discuss the possibility to discriminate among different operators that contribute to lepton flavor violating (LFV) tau decays. Correlations among decay rates in different channels are shown to provide a basic handle to unravel the origin of LFV in these processes. More information about the underlying dynamics responsible for LFV can be gathered from differential distributions in three-body decays like tau -> mu pi pi or tau -> 3 mu: these are considered in some detail. We incorporate in our analysis recent developments in the determination of the hadronic form factors for tau -> mu pi pi. Future prospects for the observation of LFV tau decays and its interpretation are also discussed.

\tau

Recently, the τ → K π ν τ decay spectrum has been measured by the Belle and BaBar collaborations. In this work, we present an analysis of such decays introducing a dispersive parametrization for the vector and scalar Kπ form factors. This allows for precise tests of the Standard Model. For instance, the determination of f + ( 0 ) | V u s | from these decays is discussed. A comparison and a combination of these results with the analyses of the K l 3 decays is also considered.

decays

We present a brief overview of the recent theoretical progress to describe the K_{l2} and K_{l3} decays. We discuss the interesting probes of the Standard Model offered by these decays such as the extraction of |V_{us}| and the test of the CKM unitarity, the tests of lepton universality, the quark mass ratio determination and the test of the electroweak couplings of the light quarks to the W-boson.

Dispersive representation of the scalar and vector Kpi form factors for tau --> K pi nu_tau and K_{l3} decays

K`4 are for several reasons an especially interesting decay channel of K mesons: K`4 decays allow an accurate measurement of a combination of S -wave ππ scattering lengths, one form factor of the decay is connected to the chiral anomaly and the decay is the best source for the determination of some low energy constants of ChPT. We present a dispersive approach to K`4 decays, which takes rescattering effects fully into account. Some fits to NA48/2 and E865 measurements and results of the matching to ChPT are shown.

Precision SM calculations and theoretical interests beyond the SM in Kl2 and Kl3 decays

decays have several features of interest: they allow an accurate measurement of ππ-scattering lengths; the decay is the best source for the determination of some low-energy constants of chiral perturbation theory (χPT); one form factor of the decay is connected to the chiral anomaly. We present the results of our dispersive analysis of decays, which provides a resummation of ππ- and Kπ-rescattering effects. The free parameters of the dispersion relation are fitted to the data of the high-statistics experiments E865 and NA48/2. By matching to χPT at NLO and NNLO, we determine the low-energy constants and . In contrast to a pure chiral treatment, the dispersion relation describes the observed curvature of one of the form factors, which we understand as an effect of rescattering beyond NNLO.

A Dispersive Treatment ofKℓ4Decays

Recently, several experimental collaborations have invested considerable effort into new and more precise measurements of the η ! 3π decays. These experimental advances require revisiting the corresponding theoretical analyses. In this work, we present a new calculation of the η ! 3π decay amplitude relying on dispersive methods. We show how the study of this decay allows one to extract a fundamental parameter of the Standard Model, namely the quark mass ratio Q 2 � (m 2 − ˆ m 2 )/(m 2 − m 2), with good precision. We find Q = 21.3� 0.6. We then discuss the

A dispersive treatment of decays

The Callan-Treiman low-energy theorem offers an opportunity to test electroweak couplings of light quarks to the gauge boson W. To that aim, we introduce a model-independent and accurate dispersive parametrization of the two K_{l3} form factors. We then discuss three applications to the analysis of K_{e3} and K_{mu3} measurements: the prediction of the ratios Gamma(K_{mu3})/Gamma(K_{e3}), the extraction of |f_+(0)V_{us}| and finally the possible measurement of m_u - m_d induced isospin breaking asymmetry.

Determination of the light quark masses from eta -\rightarrow 3 pi

Hadronic tau decays belong to the processes that show a resonance-like structure in the axial vector current in the