Radiative corrections to πl2 and Kl2 decays

Abstract

We reexamine radiative corrections to π l2 and K l2 decays. We perform a matching calculation, including vector and axial vector resonances as explicit degrees of freedom in the long distance part. By considering the dependence on the matching scale and on the hadronic parameters, and by comparing with model independent estimates, we scrutinize the model dependence of the results. For the pseudoscalar meson decay constants, we extract the values f π = (92.1±0.3) MeV and f K = (112.4±0.9) MeV. For the ratios R π and R K of the electronic and muonic decay modes, we predict R π = (1.2354 ± 0.0002) · 10 −4 and R K = (2.472 ± 0.001) · 10 −5 .

Sterile neutrinos in leptonic and semileptonic decays

“…of theoretical analyses [55,56] with the recent measurements from the NA62 collaboration [57,58] and with the existing measurements on pion leptonic decays [59] 23) suggests that observation agrees at the 1σ level with the SM predictions for…”

Simultaneous extraction of the Fermi constant and PMNS matrix elements in the presence of a fourth generation

“…Using the experimental measurements BF (π + → e + ν e (γ)) = (1.230 ± 0.004) · 10 −4 [38] (which is and average of the measurements quoted in Refs. [51][52][53]) and BF (π + → µ + ν µ (γ) = 0.9998770 ± 0.0000004 [38], and the theoretical prediction R theo π = (1.2354 ± 0.0002) · 10 −4 [54] we obtain the constraints on |U e4 |, |U µ4 |, and |U τ 4 | as shown in Figs One should note the non-trivial lower limit for |U e4 | and the non-trivial upper limit for |U E4 | where we denote the heavy charged lepton as E. The p-value for the 3SM point |U e4 | = 0 is now 2.6 %. The allowed range for G F is again tightened:…”

Effect of steriles states on lepton magnetic moments and neutrinoless double beta decay

“…The dominant contributions to these processes arise from tree-level W mediated exchanges (a consequence of the modified vertex W ν due to the presence of the sterile states). As will be discussed in the following section, among the distinct constraints derived from meson decays, the most severe bounds are due to the violation of lepton universality in leptonic kaon decays, parametrised by ∆r K , 5) and whose current value (comparison of theoretical analyses [74,75] with the recent measurements from the NA62 collaboration [68]) is…”