Phenomenology of LFV at low-energies and at the LHC: strategies to probe the SUSY seesaw

We study the impact of a type-I SUSY seesaw concerning lepton flavour violation (LFV) at low-energies and at the LHC. At the LHC, $\chi_2^0\to \tilde \ell \,\ell \to \ell \,\ell\,\chi_1^0$ decays, in combination with other observables, render feasible the reconstruction of the masses of the intermediate sleptons, and hence the study of $\ell_i - \ell_j$ mass differences. If interpreted as being due to the violation of lepton flavour, high-energy observables, such as large slepton mass splittings and flavour violating neutralino and slepton decays, are expected to be accompanied by low-energy manifestations of LFV such as radiative and three-body lepton decays. We discuss how to devise strategies based in the interplay of slepton mass splittings as might be observed at the LHC and low-energy LFV observables to derive important information on the underlying mechanism of LFV.Comment: 6 pages, 4 figures. To appear in the proceedings of the 11th International Workshop on Tau Lepton Physics (TAU2010), Manchester, UK, 13-17 September 201

Lepton flavour violation: physics potential of a Linear Collider

We revisit the potential of a Linear Collider concerning the study of lepton flavour violation, in view of new LHC bounds and of the (very) recent developments in lepton physics. Working in the framework of a type I supersymmetric seesaw, we evaluate the prospects of observing seesaw-induced lepton flavour violating final states of the type e \mu + missing energy, arising from e+ e- and e- e- collisions. In both cases we address the potential background from standard model and supersymmetric charged currents. We also explore the possibility of electron and positron beam polarisation. The statistical significance of the signal, even in the absence of kinematical and/or detector cuts, renders the observation of such flavour violating events feasible over large regions of the parameter space. We further consider the \mu-\mu- + E^T_miss final state in the e- e- beam option finding that, due to a very suppressed background, this process turns out to be a truly clear probe of a supersymmetric seesaw, assuming the latter to be the unique source of lepton flavour violation.Comment: 30 pages, 48 figure

Potential of a Linear Collider for Lepton Flavour Violation studies in the SUSY seesaw

We study the potential of an e+- e- Linear Collider for charged lepton flavour violation studies in a supersymmetric framework where neutrino masses and mixings are explained by a type-I seesaw. Focusing on e-mu flavour transitions, we evaluate the background from standard model and supersymmetric charged currents to the e mu + missing E_T signal. We study the energy dependence of both signal and background, and the effect of beam polarisation in increasing the signal over background significance. Finally, we consider the mu- mu- + missing E_T final state in e- e- collisions that, despite being signal suppressed by requiring two e-mu flavour transitions, is found to be a clear signature of charged lepton flavour violation due to a very reduced standard model background.Comment: 8 pages, 5 figures. To appear in the proceedings of "DISCRETE 2012 - 3rd Symposium on Prospects in the Physics of Discrete Symmetries", Lisbon, Portugal, 3-7 December 201

Lepton Number Violating Radiative WW Decay in Models with R-parity Violation

Models with explicit R-parity violation can induce new rare radiative decay modes of the $W$ boson into single supersymmetric particles which also violate lepton number. We examine the rate and signature for one such decay, $W\rightarrow \tilde l\gamma$, and find that such a mode will be very difficult to observe, due its small branching fraction, even if the lepton number violating coupling in the superpotential is comparable in strength to electromagnetism. This parallels a similar result obtained earlier by Hewett in the case of radiative $Z$ decays.Comment: 10 pages, 2 figures(available on request), LaTex, ANL-HEP-PR-92-8

Production and decays of supersymmetric Higgs bosons in spontaneously broken R-parity

We study the mass spectra, production and decay properties of the lightest supersymmetric CP-even and CP-odd Higgs bosons in models with spontaneously broken R-parity (SBRP). We compare the resulting mass spectra with expectations of the Minimal Supersymmetric Standard Model (MSSM), stressing that the model obeys the upper bound on the lightest CP-even Higgs boson mass. We discuss how the presence of the additional scalar singlet states affects the Higgs production cross sections, both for the Bjorken process and the "associated production". The main phenomenological novelty with respect to the MSSM comes from the fact that the spontaneous breaking of lepton number leads to the existence of the majoron, denoted J, which opens new decay channels for supersymmetric Higgs bosons. We find that the invisible decays of CP-even Higgses can be dominant, while those of the CP-odd bosons may also be sizeable.Comment: 21 pages, 8 figures; minor changes, final version for publicatio

Degenerate neutrinos from a supersymmetric A_4 model

We investigate the supersymmetric A_4 model recently proposed by Babu, Ma and Valle. The model naturally gives quasi-degenerate neutrinos that are bi-largely mixed, in agreement with observations. Furthermore, the mixings in the quark sector are constrained to be small, making it a complete model of the flavor structure. Moreover, it has the interesting property that CP-violation in the leptonic sector is maximal (unless vanishing). The model exhibit a close relation between the slepton and lepton sectors and we derive the slepton spectra that are compatible with neutrino data and the present bounds on flavor-violating charged lepton decays. The prediction for the branching ratio of the decay tau -> mu gamma has a lower limit of 10^{-9}. In addition, the overall neutrino mass scale is constrained to be larger than 0.3 eV. Thus, the model will be tested in the very near future.Comment: 11 pages, 6 figures. Talk given at the International Workshop on Astroparticle and High Energy Physics (AHEP), Valencia, Spain, 14-18 Oct. 200