Related papers: E+ E- -> Tau+ Tau- at the Threshold and Beyond
A long-standing problem with the solution of the Schr\"odinger equation has been its inability to account for the electron-positron annihilation in positron hydrogen scattering above the positronium formation threshold. This letter shows…
A detailed, model-independent study of CP violation at present and future electron-positron colliders is reported. Firstly, we investigate CP violation effects in $W$ boson and $t$ quark pair production in $e^+e^-$ annihilation and in…
We investigate $e^+ e^- \to t\bar t$ by taking into account wave function distortion effects in the near-threshold region and interpolating the correction factor to the high-energy perturbative QCD region. The strong color attraction…
From the total cross section for the reaction $e^+e^-\to \tau^+\tau^-\gamma$ at the $Z_1$ pole and in the framework of a simplest little Higgs model (SLHM), we get a limit on the characteristic energy scale of the model $f$, $f \geq 5.4$…
The role of the effective momentum approximation to disentangle Coulomb distortion effects in quasielastic $(e,e')$ reactions is investigated. The separation of the cross section in longitudinal and transverse components is discussed…
A technique to deal with Coulomb electron distortions in the analysis of (e,e'p) reactions is presented. Thereby, no approximations are made. The suggested technique relies on a partial-wave expansion of the electron wave functions and a…
In these proceedings a recent calculation of the last missing piece of the two-loop O(alpha alpha(s)) corrections to gamma t anti-t vertex at the t anti-t threshold due to the exchange of a W boson and a gluon is summarised. The calculation…
We calculate distributions for tau+ tau- gamma production at LEP 1 taking into account a potentially existing anomalous magnetic moment a_tau of the tau lepton. The existing upper limits for |a_tau| are known from the dependence of the…
In bilinear R-Parity violating models where a term \epsilon_3L_3H_2 is introduced in the superpotential, the tau lepton can mix with charginos. We show that this mixing is fully compatible with LEP1 precision measurements of the Z\tau\tau…
The most interesting theoretical features of W-pair production in e+e- collisions are reviewed. Based on an analysis of on-shell W-pairs, it is shown that the mere inclusion of leading $O(\alpha)$ corrections--such as initial-state…
We review our recent works on tests of perturbative QCD, inspired by the relation between the hadronic decay of the tau lepton and the e+ e- annihilation into hadrons. First, we present a set of commensurate scale relations that probe the…
We derive an upper limit on the electric dipole moment (EDM) of the tau-lepton, which follows from the precision measurements of the electron EDM.
We search for lepton flavour violating events (e mu, e tau and mu tau) that could be directly produced in e+e- annihilations, using the full available data sample collected with the OPAL detector at centre-of-mass energies between 189 GeV…
In previous studies of the theory of Coulomb excitation, the term in the electromagnetic interaction which is quadratic in the vector potential has been ignored. In this paper, we use qualitative arguments and detailed numerical…
A higher order QED calculation of the ultraperipheral heavy ion cross section for mu+ mu- pair production at RHIC and LHC is carried out. The so-called "Coulomb corrections" lead to an even greater percentage decrease of mu+ mu- production…
The change of the probability of proton emission in nuclear photoeffect due to an intense coherent (laser) field is discussed near the threshold, where the hindering effect of the Coulomb field of the remainder nucleus is essential. The…
Pair production of tau leptons in two photon collision ${\gamma\gamma \to \tau^{+}\tau}^{-}$ is studied at CLIC to test CP violating QED couplings of tau leptons. CP violating effects are investigated using tau pair spin correlations which…
It was reported that the NNLO correction to the total cross section near the ttbar threshold in e+e- collisions is as large as the NLO correction to it. In the thesis, we improve the convergence of the perturbative series of the total cross…
Recent results on production and decays of polarized top quarks are reviewed. Top quark pair production in $e^+e^-$ annihilation is considered near energy threshold. For longitudinally polarized electrons the produced top quarks and…
The possible anomalous New Physics contributions to magnetic and electric dipole moments of the $\tau$ lepton have brought renewed interest in studying $\tau$-pair production at energies of the LHC and future colliders. We discuss effects…