Radiative corrections to muon and beta decay in the intermediate Vector Boson theory

The radiative corrections to muon and beta decay are examined in detail using the ξ-limiting formalism ofLee andYang. The electron spectra for both decays are calculated. It is found that the muon lifetime discrepancy is reduced considerably if one considers, quantitatively, the effect of strong interactions on the weak vector coupling constant as determined from the neutron's lifetime.     

Radiative corrections to positronium decay

In this work a method for calculating radiative corrections to positronium decay is presented that is direct, and allows for a systematic extension applicable to the calculation of corrections beyond the first [o(α)] correction. An expression for the decay amplitude in terms of the Bethe-Salpeter wavefunction is employed. The Bethe-Salpeter wavefunction is evaluated perturbatively in a scheme having a lowest-order bound state equation that is exactly soluble. The decay amplitude is evaluated in Coulomb gauge, without the introduction of a photon mass. One-loop renormalization in Coulomb gauge is shown to be consistent. Using this method the known analytic result for the o(α) correction to the parapositronium decay rate is obtained. The same method is applied to orthopositronium, and the existing theoretical discrepancy in the value of the o(α) correction to the decay rate is resolved. This o(α) correction is obtained with an error which corresponds to an uncertainty in the total rate much smaller than α²Γ_LO (where Γ_LO is the lowest-order rate). Also, the o(α) correction to the differential decay rate is computed for the first time.     

Radiative corrections to parapositronium decay

Radiative corrections to the two-gamma decay of parapositronium are examined. Special care is taken in the handling of the so-called binding diagram; in particular, the limiting procedure related to the infrared divergence is considered carefully. The general covariant gauges and the Fried-Yennie gauge are used in the computation to see that gauge invariance is accounted for. The order α correction of Harris and Brown is confirmed. In addition, from a sharp peak of the matrix element at low momentum and the low-momentum correction to the wave function, an α² ln α^?1 correction is derived.     

Radiative neutrino decay in superstring models

The rate for the radiative decay of neutrinos is calculated in E₆ superstring models with light colour triplet isosinglets h and h. In contrast to the standard model, the rate is not suppressed either by the GIM mechanism or by helicity matching. Comparison with astrophysical data allows one to set an upper limit on the Yukawa couplings QL and λd^cv^ch. Taking it is found that , compatible with m_vc, m_vμ in the range 10–100 eV. From the cosmological requirement of not photo-ionizing light elements after nucleosynthesis, it follows that the v_τ must lie in the same mass range and consequently .     

Radiative neutralino decay in split supersymmetry

Radiative neutralino decay $\chi^{0}_{2}\longrightarrow\chi^{0}_{1}\gamma$ is studied in a Split Supersymmetric scenario, and compared with mSUGRA and MSSM. This one-loop process has a transition amplitude which is often quite small, but it has the advantage of providing a very clear and distinct signature: electromagnetic radiation plus missing energy. In Split Supersymmetry this radiative decay is in direct competition with the tree-level three-body decay $\chi^{0}_{2}\longrightarrow\chi^{0}_{1}f\bar{f}$ , and we obtain large values for the branching ratio $B(\chi^{0}_{2}\longrightarrow\chi^{0}_{1}\gamma)$ which can be close to unity in the region M ₂～M ₁, something already seen in the MSSM. Furthermore, the values for the radiative and the tree-level neutralino decay branching ratios have a strong dependence on the logarithm of the split supersymmetric scale $\widetilde{m}$ , which otherwise is very difficult to infer from experimental observables.     

Radiative tau decay into pion

The possibility of the experimental investigation of the radiative tau decay into pion is discussed including background conditions. The decay width is estimated to be Br(τ→v _τ π γ)=0.15% (at the minimal registered photon energy 50 MeV). The contribution of the structural component is 10% of the total radiation. The main background is produced by photons from the τ→v _τ π ^? π ⁰ decay. We investigate the angular and energy spectra of the decay products and analyse the background conditions. The kinematic region was found where the structural radiation dominates over background.     

Measurement of the Lambda b lifetime in the exclusive decay Lambda b --> J/psi Lambda

We have measured the Lambda b lifetime using the exclusive decay Lambda b --> J/psi Lambda, based on 1.2 fb(-1) of data collected with the D0 detector during 2002-2006. From 171 reconstructed Lambda b decays, where the J/psi and Lambda are identified via the decays J/psi --> mu+ mu- and Lambda --> ppi, we measured the Lambda b lifetime to be tau(Lambda b)=1.218 (+0.130)/(-0.115) (stat) +/- 0.042(syst) ps. We also measured the B0 lifetime in the decay B0 --> J/psi(mu+ mu-)K(0)/(S)(pi+ pi-) to be tau(B0)=1.501 (+0.078)/(-0.074) (stat) +/- 0.050(syst) ps, yielding a lifetime ratio of tau(Lambda b)/tau(B0)=0.811 (+0.096)/(-0.087) (stat) +/- 0.034(syst).     

Measurement of decay parameters for Xi- --> Lambda pi- decay

Based on 1.35 x 10(6) polarized Xi(-) events, we measure the parameter phi(Xi) to be -1.61 degrees +/-2.66 degrees +/-0.37 degrees for the Xi(-)-->Lambda pi(-) decay. New results for the parameters beta(Xi) and gamma(Xi) are also presented. Assuming that the CP-violating phase difference is negligible, we deduce the strong phase difference between the P-wave and S-wave amplitudes of the Lambda pi final state to be 3.17 degrees +/-5.28 degrees +/-0.73 degrees, reducing the uncertainty in estimating the level of CP violation in Xi-hyperon decay.     

Radiative corrections to the light muonic atoms decay rate

Radiative corrections to the decay rate in low-Z hydrogen-like muonic atoms are considered. The correction is due to the Uehling potential and it has the relative order of α. The numerical results are reported for the 2p → 1s transition for atoms with nuclear charge up to Z = 10.     

Soft-breaking correction to hard supersymmetric relations QCD correction to squark decay

Supersymmetric relations between dimensionless couplings receive finite correction at one-loop when supersymmetry is broken softly. We calculate theO (α _s) correction to the squark decay width to a quark and an electroweak gaugino, which is found to be nonvanishing. Logarithmic correction appears when the gluino is heavy.     

Coulomb corrections to nuclear beta decay

A calculation of the Coulomb correction to the nuclear beta decay is presented, in the context of the elementary-particle treatment of Kim and Primakoff, making use of the low-energy approximants to nuclear form factors.     

Sharpening low-energy, standard-model tests via correlation coefficients in neutron beta decay.

The correlation coefficients a, A, and B in neutron beta decay are proportional to the ratio of the axial-vector-to-vector weak coupling constants, gA/gV, to leading recoil order. With the advent of the next generation of neutron-decay experiments, the recoil-order corrections to these expressions become experimentally accessible, admitting a plurality of standard model (SM) tests. The measurement of both a and A, e.g., allows one to test the conserved-vector-current (CVC) hypothesis and to search for second-class currents (SCC) independently. The anticipated precision of these measurements suggests that the bounds on CVC violation and SCC from studies of nuclear beta decay can be qualitatively bettered.     

Radiative kaon decay in the chiral perturbation theory

We analyze the possibility of experimental investigation of new low-energy relations between the values of resonance masses in the meson form factors and the differential rate of radiative kaon decay K ⁺ → π⁺ e ⁺ e ⁻(μ⁺μ⁻) at the current level of the experimental precision. A set of arguments is listed in favor that these relations can be a consequence of weak static interactions in the Standard Model. The results were presented at the 5th NA48 Mini-Workshop on Kaon Physics, CERN, Dec. 12, 2006. The text was submitted by the authors in English.