Radiative Corrections to Decay Processes

On the precise determination of the Fermi coupling constant from the muon lifetime

“…An exact expression for the full electron mass dependence in ∆q (1) has been given by Nir [13]. Starting from the expressions for the 1-loop QED corrections to the electron spectrum given by Behrends et al [9] and, after taking into account the correction given in Appendix C of Ref. [11], we obtain complete agreement with Eq.…”

“…This argument was used by Roos and Sirlin [8] to show that terms odd in m e would cancel between vector and axial-vector contributions in the expression for the differential decay rate. They then went on to show, by direct examination of known analytic form of the differential decay rate [9], that the phase-space integration could not generate terms linear in m e and thus that the leading electron mass corrections at 1-…”

Precise prediction forMWin the MSSM

“…(1) as well as the (numerically insignificant) term 3m 2 µ /(5M 2 W ) arising from the tree-level W propagator. The precise measurement of the muon lifetime and the equivalently precise calculation of ∆ QED [36,37] thus provide the accurate value G µ = (1.16637 ± 0.00001 × 10 −5 ) GeV −2 .…”

Light mesons and muon radiative decays and photon polarization asymmetry

“…A remarkable aspect of the results in Eq. (19), is that in the limit in which λ → 0 and x → 1, which corresponds to the emission of low energy positron and hard photons at relative small angles in the meson rest frame, the contribution proportional to f L IB (x, λ) and to f L INT (x, λ) distributions dominates in the decay rate. In other words, hard photons will be mainly produced with left-handed polarizations.…”

“…Then in this limit both the left-handed or right-handed distributions should tend to the same value, as indeed can be verified by performing the limit x → 0 on the density distributions in Eq. (19). In the following we will show how this property could be relevant in order to define an observable which is free from infrared (E γ → 0) singularity, namely the photon polarization asymmetry.…”