Precision physics at LEP

Two-Loop QED Corrections to the Scattering of Four Massive Leptons

We study two-loop corrections to the scattering amplitude of four massive leptons in quantum electrodynamics. These amplitudes involve previously unknown elliptic Feynman integrals, which we compute analytically using the differential equation method. In doing so, we uncover the details of the elliptic geometry underlying this scattering amplitude and show how to exploit its properties to obtain compact, easy-to-evaluate series expansions that describe the scattering of four massive leptons in QED in the kinematical regions relevant for Bhabha and Møller scattering processes.

Two-loop corrections to Bhabha scattering

The two-loop radiative photonic corrections to Bhabha scattering are computed in the leading order of the small electron mass expansion up to the nonlogarithmic term. After including the soft photon bremsstrahlung, we obtain the infrared-finite result for the differential cross section, which can directly be applied to a precise luminosity determination of the present and future e+ e- colliders.

Model-independent analysis of muon g(mu) - 2

We consider possible physics beyond the standard model that could account for the large recently reported [Muon g-2 Collaboration, H. N. Brown et al., Phys. Rev. Lett. 86, 2227 (2001)] effect in g(mu)-2. If the underlying theory can be treated perturbatively, then the only possibilities are models that contain particles that yield "direct" contributions, e.g., supersymmetric models, models with unexpectedly light leptoquarks, or with a rather exotic heavy vector boson. If the underlying theory involves strong interactions, as in technicolor models, then the discrepancy could be accounted for by a variety of mechanisms.