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Register a new userBounds on fourth generation induced Lepton Flavour Violating double insertions in Supersymmetry
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We derive bounds on leptonic double mass insertions of the type $delta^{l}_{i4} delta^{l}_{4j}$ in four generational MSSM, using the present limits on $l_i to l_j + gamma$. Two main features distinguish the rates of these processes in MSSM4 from MSSM3 : (a) tan$beta$ is restricted to be very small $lesssim 3 $ and (b) the large masses for the fourth generation leptons. In spite of small $tanbeta$, there is an enhancement in amplitudes with $llrr$($delta_{i4}^{ll}delta_{4j}^{rr}$) type insertions which pick up the mass of the fourth generation lepton, $m_{tau}$. We find these bounds to be at least two orders of magnitude more stringent than those in MSSM3.
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This dissertation reviews the Standard Model formalism as well as the Lepton Flavour Violating (LFV) decay processes which cause its extension, known as the physics beyond the SM. Firstly, using the experimental bounds on three body LFV decays, the corresponding bounds on two body LFV decays are reviewed. The dynamical suppression of three body LFV decays due to momentum dependent couplings is also reviewed. Secondly, the role of the LFV decays to explain the LSND excess is discussed in detail, for which the experimental bounds on three body LFV decays, i.e. mu -> 3e are used to constraint the coupling tilde{g}_{Z_{mu e}}, which is needed to calculate the anomalous muon decay mu -> e u_lbar{ u}_l. Then comparing the effective coupling of anomalous muon decay to r>1.6times 10^{-3} [9809524], it is proved that LFV is not the correct hypothesis to explain the LSND excess. Finally, LFV decays at loop order are studied in Seesaw model of neutrino masses [PRL. 86 2502 (2001)] where the smallness of the Seesaw neutrino mass may be naturally realized with m_N (mass of right-handed singlet neutrinos) of order 1 TeV. It is shown that the Higgs mass of a new scalar doublet with lepton number L=-1 needed in the model has to be larger than 50 TeV to get the branching ratio of mu -> 3e to be consistent with the existing bound on mu -> 3e. This defeats the original motivation of the model, namely that there is no physics beyond the TeV energy scale.
The MEG Experiment searches for a lepton flavour violating decay, $mu^+tomathrm{e}^+gamma $, with a branching-ratio sensitivity of $10^{-13}$ in order to explore the parameter region predicted by many theoretical models beyond the Standard Model. Detector construction and the Engineering Run were completed in 2007, and the first Physics Run will be carried out in 2008. In this paper, the prospects of MEG Physics Run in 2008 is described in addition to the experimental overview.
Many models for physics beyond the Standard Model predict lepton-flavour violating decays of charged leptons at a level which may become observable very soon. In the present paper we investigate the decays of a Tau into three charged leptons in a generic way, based on effective-field-theory methods, where the relevant operators are classified according to their chirality structure. We work out the decay distributions and discuss phenomenological implications.
In this work we study the Lepton Flavour Violating semileptonic $tau$ decays: 1) $tau to mu PP$ with $PP= pi^+pi^-, pi^0pi^0, K^+K^-, K^0 {bar K}^0$; 2) $tau to mu P$ with $P=pi^0, eta, eta$ and 3) $tau to mu V$ with $V = rho^0, phi$. We work within the context of two constrained MSSM scenarios: the CMSSM and NUHM. A full one-(SUSY)loop computation is presented and the importance of the various contributions, the $gamma$-, $Z$-, and Higgs bosons mediated ones are analysed. The hadronization of quark bilinears is performed within the chiral framework. Some discrepancies in the predicted rates for BR($tau to mu eta$), BR($tau to mu eta$) and BR($tau to mu K^+K^-$) are found with respect to previous estimates, which will be commented here. These three channels will be shown to be the most competitive ones to test simultaneously the Lepton Flavour Violation and the Higgs sector. We further present here a set of approximate formulas for all the semileptonic channels which we believe can be useful for further comparison with present and future data.
I present a general exclusion bound for the Higgs in fourth generation scenarios with a general lepton sector. Recent Higgs searches in fourth generation scenarios rule out the entire Higgs mass region between 120 and 600 GeV. That such a large range of Higgs masses are excluded is due to the presence of extra heavy flavors of quarks, which substantially increase Higgs production from gluon fusion over the Standard Model rate. However, if heavy fourth generation neutrinos are less than half of the Higgs mass, they can dominate the Higgs decay branching fraction, overtaking the standard Higgs to WW* decay rate. The Higgs mass exclusion in a fourth generation scenario is shown most generally to be 155-600 GeV, and is highly dependent on the fourth generation neutrino mixing parameter.
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