Multiphoton signals of a (96 GeV?) stealth boson

Cascade decays of new scalars into final states with multiple photons and possibly quarks may lead to distinctive experimental signatures at high-energy colliders. Such signals are even more striking if the scalars are highly boosted, as when produced from the decay of a much heavier resonance. We study this type of events within the framework of the minimal stealth boson model, an anomaly-free $\text{U}(1)_{Y'}$ extension of the Standard Model with two complex scalar singlets. It is shown that, while those signals may have cross sections that might render them observable with LHC Run 2 data, they have little experimental coverage. We also establish a connection with a CMS excess observed in searches for new scalars decaying into diphoton final states near 96 GeV. In particular, we conclude that the predicted multiphoton signatures are compatible with such excess.Comment: LaTeX 32 pages. Comments added and discussions extended. Final version in EPJ

A closer look at the possible CMS signal of a new gauge boson

The CMS collaboration has recently reported a 2.8$\sigma$ excess of $eejj$ events with an invariant mass around 2 TeV. This observation can be explained in the context of standard model extensions with new gauge bosons $W'$, $Z'$ and heavy neutrinos coupling (mainly) to the electron. We discuss additional signals that allow to confirm or discard the $W'$ and $Z'$ hypotheses.Comment: ReVTeX 5 page

A new bridge between leptonic CP violation and leptogenesis

Flavor effects due to lepton interactions in the early Universe may have played an important role in the generation of the cosmological baryon asymmetry through leptogenesis. If the only source of high-energy CP violation comes from the left-handed leptonic sector, then it is possible to establish a bridge between flavored leptogenesis and low-energy leptonic CP violation. We explore this connection taking into account our present knowledge about low-energy neutrino parameters and the matter-antimatter asymmetry observed in the Universe. In this framework, we find that leptogenesis favors a hierarchical light neutrino mass spectrum, while for quasi-degenerate and inverted hierarchical neutrino masses there is a very narrow allowed window. The absolute neutrino mass scale turns out to be m < 0.1 eV.Comment: 10 pages, 3 figure

Lepton flavour violation in the supersymmetric type-II seesaw mechanism

We summarize the predictions for the radiative decays l_j->l_i \gamma within the context of the supersymmetric type II seesaw mechanism considering universal boundary conditions for the soft SUSY breaking terms. The dependence on the low-energy neutrino parameters is discussed and the deviations from the analytical results for large $\tan\beta$ analyzed.Comment: 3 pages, 4 figures. To appear in the proceedings of 16th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY08), Seoul, Korea, 16-21 Jun 200