Results

Thesis & Dissertations

Loop Correction Effects in Extensions of MSSM with Vector like Generation

Abstract

An analysis of the Dirac neutrino magnetic moment in minimal supersymmetric standard model extension, with a vectorlike lepton generation is discussed. The current experimental limits on the neutrino magnetic moments are orders of magnitude larger than the prediction with the standard model interactions and thus its test appears out of reach. We compute the moments arising from the exchange of W and the charged leptons in the loop, as well as from the exchange of charginos, charged sleptons and charged mirror sleptons. It is shown that the neutrino moment in our model can be several orders of magnitude larger than what the standard model predicts, lying close to and below the current experimental upper limits and should be accessible in improved future experiment. A correlated prediction of the heaviest neutrino lifetimes from radiative decays to the lighter neutrinos via exchange of charginos and sleptons in the loops is also made. The predicted lifetimes are several orders of magnitude smaller than the one with the standard model interactions and also lie close to the current experimental limits from analyses using the cosmic background neutrino data. Within the same framework, a discussion of the electron EDM is carried out to probe the possibility of new physics beyond the standard model. We focus on the electric dipole moment of the electron since the limit on it is the most stringent. Further, theoretical computations of it are free of QCD uncertainties. The analysis presented here first explores the probe of high scales via electron electric dipole moment (EDM) within MSSM where the contributions to the EDM arise from the chargino and the neutralino exchanges in loops. Here it is shown that the electron EDM can probe mass scales from tens of TeV into the PeV range. The analysis is then extended to include a vectorlike generation which can mix with the three ordinary generations. Here new CP phases arise and it is shown that the electron EDM now has not only a supersymmetric contribution from the exchange of charginos and neutralinos but also a non-supersymmetric contribution from the exchange of W and Z bosons. It is further shown that the interference of the supersymmetric and the non-supersymmetric contribution leads to the remarkable phenomenon where the electron EDM as a function of the slepton mass rst falls and become vanishingly small and then rises again as the slepton mass increases. This phenomenon arises as a consequence of cancellation between the SUSY and the non-SUSY contribution at low scales while at high scales the SUSY contribution dies out and the EDM is controlled by the non-SUSY contribution alone. The high mass scales that can be probed by the EDM are far in excess of what accelerators will be able to probe. The sensitivity of the EDM to CP phases both in the SUSY and the non-SUSY sectors are also discussed. The u --->ey branching ratio is also analyzed to show the validity of our model where we impose the constraints on the neutrino masses and keep the electron EDM in check. The mixing with the mirrors allows the possibility of this decay here. The analysis is done at the one loop level with the exchange of charginos and neutralinos and of sleptons and mirror sleptons in the loops. A one loop analysis with W and Z boson exchange and mirror leptons and neutrinos is also considered. The effects of CP violating phases from the new sector on the decay u ---> e + y are analyzed in detail. The constraints arising from the current upper limit on the branching ratio B( ! e + ) from the MEG experiment on the parameter space of SUSY models and on vectorlike models are explored. Further, the MEG experiment is likely to improve the upper limit by an order of magnitude in the coming years. The improved limits will allow one to probe a much larger domain of the parameter space of the extended models.

Student(s)

Ahmad Kamal Itani

Supervisor(s)

Ramadan Khamice Awad, Mohammad Riad Saker