Search

We discuss several manifestations of charged lepton flavour violation at high energies. Focusing on a supersymmetric type I seesaw, considering constrained and semi-constrained supersymmetry breaking scenarios, we analyse different observables, both at the LHC and at a future Linear Collider. We further discuss how the synergy between low- and high-energy observables can shed some light on the underlying mechanism of lepton flavour violation., Comment: 6 pages, 6 figures. To appear in the proceedings of the "Linear Collider Workshop - LC13", ECT* Trento, 16 - 20 September 2013

It has been pointed out that supersymmetric extensions of the Standard Model can induce significant changes to the theoretical prediction of the ratio $��(K\rightarrow e��)/��(K\rightarrow����)\equiv R_{K}$, through lepton flavour violating couplings. In this work we carry out a full computation of all one-loop corrections to the relevant $��\ell H^{+}$ vertex, and discuss the new contributions to $R_{K}$ arising in the context of different constrained (minimal supergravity inspired) models which succeed in accounting for neutrino data, further considering the possibility of accommodating a near future observation of a $��\to e��$ transition. We also re-evaluate the prospects for $R_{K}$ in the framework of unconstrained supersymmetric models. In all cases, we address the question of whether it is possible to saturate the current experimental sensitivity on $R_{K}$ while in agreement with the recent limits on $B$-meson decay observables (in particular BR($B_{s}\to��^+��^-$) and R($B_{u}\to����$)), as well as BR($��\to e ��$) and available collider constraints. Our findings reveal that in view of the recent bounds, and even when enhanced by effective sources of flavour violation in the right-handed $\tilde{e}-\tilde��$ sector, constrained supersymmetric (seesaw) models typically provide excessively small contributions to $R_{K}$. Larger contributions can be found in more general settings, where the charged Higgs mass can be effectively lowered, and even further enhanced in the unconstrained MSSM. However, our analysis clearly shows that even in this last case SUSY contributions to $R_{K}$ are still unable to saturate the current experimental bounds on this observable, especially due to a strong tension with the $B_{u}\to����$ bound., Revised version reflects the published article. 26 pages, 7 Figures in Encapsulated Postscript

We calculate the relic density of the lightest neutralino in a supersymmetric seesaw type-II (``triplet seesaw'') model with minimal supergravity boundary conditions at the GUT scale. The presence of a triplet below the GUT scale, required to explain measured neutrino data in this setup, leads to a characteristic deformation of the sparticle spectrum with respect to the pure mSugra expectations, affecting the calculated relic dark matter (DM) density. We discuss how the DM allowed regions in the (m_0,M_{1/2}) plane change as a function of the (type-II) seesaw scale. We also compare the constraints imposed on the models parameter space form upper limits on lepton flavour violating (LFV) decays to those imposed by DM. Finally, we briefly comment on uncertainties in the calculation of the relic neutralino density due to uncertainties in the measured top and bottom masses., Comment: 20 pages, 21 Figures in Encapsulated Postscript

In models with substructure in the fermionic sector, excited fermion states are expected. Excited leptons could be produced in the interaction of high energy quasi-horizontal cosmic neutrinos with the atmosphere via neutral and charged current processes, $\nu N \to \nu^* X$ and $\nu N \to \ell^* X$. The hadronic component X, and possibly part of the excited lepton decay products, would originate an extensive air shower, observable in large cosmic ray experiments. In this paper, the sensitivity of present and planned very high energy cosmic ray experiments to excited lepton production is estimated and discussed., Comment: v1 - 26 pages,8 figures. v2 - 22 pages, 9 figures. (v2 in single spacing) Changes from v1: - New sensitivity curves, including results for third family excited leptons and double bang signature. - Added LEP results for excited electron indirect search. - Minor text modifications

The simplest unified extension of the Minimal Supersymmetric Standard Model with bilinear R--Parity violation provides a predictive scheme for neutrino masses which can account for the observed atmospheric and solar neutrino parameters. Despite the smallness of neutrino masses R-parity violation is observable at present and future high-energy colliders, providing an unambiguous cross-check of the model., Comment: 18 pages, 38 Figures in Postscript. Talk given at the International Workshop on Astroparticle and High Energy Physics, Valencia, Spain, 14-18 October 2003, to appear in JHEP Proceedings. Uses JHEP3 LaTeX class. Added a reference, 2 Figures and a new subsection

Talk presented at the XXIX Rencontres de Moriond, Electroweak Interactions and Unified Theories, March 12-19, 1994, Meribel, Comment: FTUV/94-28 IFIC/94-26, 6 pages + two figures (.ps files included)

The simplest unified extension of the Minimal Supersymmetric Standard Model with bilinear R-Parity violation provides a predictive scheme for neutrino masses which can account for the observed atmospheric and solar neutrino anomalies. Despite the smallness of neutrino masses R-parity violation is observable at present and future high-energy colliders, providing an unambiguous cross-check of the model., Comment: Talk given by JCR at the Corfu Summer Institute, September 2001, Corfu, to appear in the Proceedings. 10 pages, Latex, 16 eps figures