Electromagnetic radiative corrections to the electron-neutrino, electron, and neutrino asymmetry coefficients in neutron fl decay are calculated. Strong-interaction effects are retained as suggested by Sirlin

We study the radiative decay Z → ννγ within an effective Lagrangian approach. Using the search for energetic single-photon events in the data collected by the L3 Collaboration, we get direct bounds on dimension-six and dimension-eight operators associated with the τ -neutrino magnetic moment and the anomalous electromagnetic properties of the Z boson. As a by-product of our calculation, we reproduce the L3 result for the bound on µ ντ .The effective Lagrangian approach concerning the local SU(2) L × U(1) Y symmetry linearly realized [1] has been used recently to explore the consequences of physics beyond the Standard Model (SM) at lepton [2], hadron [3] and γγ colliders [4]. Also, this approach has been used to constrain the anomalous electromagnetic couplings of the W boson, the t quark [5] and the neutrinos [6] from the known experimental bounds on the rare decays b → sγ [7] and µ → eγ [8]. In the present letter we point out that the recent measurement of energetic single-photons at LEP arising from the radiative decay Z → ννγ [9] leads to direct constraints on dimension-eight and dimensionsix operators associated with the anomalous electromagnetic properties of the Z vector boson and the τ -neutrino magnetic moment, respectively.The radiative decay Z → ννγ can not be induced at the tree level in the SM. In the effective Lagrangian approach this decay could proceed through

The radiative corrections to first order in a to the three-body semileptonic decays of pseudoscalar mesons, M,,, are treated in a general fashion, which is suitable for model-independent experimental analysis. Special attention is paid to the energy dependence of the form factors involved. No approximation is made about the smallness of the fourmomentum transfer. As an application an expression for the energy spectrum of the charged lepton is derived. The procedure developed in this paper is valid for v,,, K,:, Dl;, or any charged M , , decay, 1 being an electron or a muon, provided hard bremsstrahlung photons are experimentally discriminated.

We examine the decay of Z 1 in electrons with recent data from LEP. The partial width Γ(Z 1 → e − e + ) is studied in the framework of a left-right symmetric model with standard electroweak corrections. Processes measured near the resonance has served to measure the neutral coupling constants very precisely, which is useful to set bounds on the parameters of the model. This partial decay occurs in the resonance zone. As a consecuence the process is independent of the mass of the additional Z 2 heavy gauge boson which appears in this kind of models and so we have the mixing angle φ between the left and the right bosons as the only additional parameter. In this paper we take advantage of this fact to set a bound for φ: −9 × 10 −3 ≤ φ ≤ 4 × 10 −3 , which is in agreement with other constraints previously reported.

We study some phenomenological constraints on the parameters of a left right model with mirror fermions (LRMM) that solves the strong CP problem. In particular, we evaluate the contribution of mirror neutrinos to the invisible Z decay width (Γ inv Z ), and we find that the present experimental value on Γ inv Z , can be used to place an upper bound on the Z-Z ′ mixing angle that is consistent with limits obtained previously from other low-energy observables. In this model the charged fermions that correspond to the standard model (SM) mix with its mirror counterparts. This mixing, simultaneously with the Z-Z ′ one, leads to modifications of the Γ(Z → ff ) decay width. By comparing with LEP data, we obtain bounds on the standard-mirror lepton mixing angles. We also find that the bottom quark mixing parameters can be chosen to fit the experimental values of R b , and the resulting values for the Z-Z ′ mixing angle do not agree with previous bounds. However, this disagreement disappears if one takes the more recent ALEPH data.14.60. St,14.60.Pq,12.15.Ff,10.30.Er,