Probing leptogenesis

The focus of this paper lies on the possible experimental tests of leptogenesis scenarios. We consider both leptogenesis generated from oscillations, as well as leptogenesis from out-of-equilibrium decays. As the Akhmedov–Rubakov–Smirnov (ARS) mechanism allows for heavy neutrinos in the GeV range, this opens up a plethora of possible experimental tests, e.g. at neutrino oscillation experiments, neutrinoless double beta decay, and direct searches for neutral heavy leptons at future facilities. In contrast, testing leptogenesis from out-of-equilibrium decays is a quite difficult task. We comment on the necessary conditions for having successful leptogenesis at the TeV-scale. We further discuss possible realizations and their model specific testability in extended seesaw models, models with extended gauge sectors, and supersymmetric leptogenesis. Not being able to test high-scale leptogenesis directly, we present a way to falsify such scenarios by focusing on their washout processes. This is discussed specifically for the left–right symmetric model and the observation of a heavy [Formula: see text], as well as model independently when measuring [Formula: see text] washout processes at the LHC or neutrinoless double beta decay.

STUDY OF e+e− INTERACTIONS AT CENTER-OF-MASS ENERGIES OF 130 AND 136 GeV

At the end of 1995, the LEP collider at CERN was operated at center-of-mass energies of 130 and 136 GeV and data corresponding to about 6 pb−1 were collected by each of the four LEP experiments. The cross-sections for fermion-pair production processes and the forward-backward asymmetries for charged lepton pairs were measured and compared to the standard model predictions. Events containing only energetic photons in the final state were used to look for effects arising from new physics. Direct searches for new particles predicted by various models beyond the standard model were performed. Searches for pair or singly produced excited leptons, for unstable charged and neutral heavy leptons, and for supersymmetric particles (chargino, neutralino, scalar leptons and scalar top quark) resulted in new exclusion limits. The ALEPH collaboration reported an excess of four-jet events in its data, which was not confirmed by the other LEP experiments.