Dipole moments of tau as a sensitive probe for beyond standard model physics

Abstract

CP violating dipole moments of leptons vanish at least to three loop order and are estimated to be $({m_l\over Mev})\times 1.6\times 10^{- 40}$ e-cm in the standard model (SM), where $m_l$ is the mass of the lepton. However they can receive potentially large contributions in some beyond SM scenarios and this makes them very sensitive probes of new physics. In this article we show that a non universal interaction, involving leptoquarks to the quark-lepton pair of the third generation through helicity unsuppressed couplings of the order of ordinary gauge couplings, can generate electric and weak dipole moments of the order of $10^{-19}$ e-cm for the tau lepton. This is greater than pure supersymmetric (SUSY) and left-right (L-R) contributions by almost three orders of magnitude. It is also greater than mirror fermionic contribution by an order of magnitude. The measurements of $\dzt$ and $\dgt$ at LEP, SLC and TCF are expected to reach sensitivities of $10^{-18}$ e-cm and $10^{-19}$ e-cm respectively in near future. The observation of a non vanishing dipole moment of tau at these facilities would therefore strongly favour superstring inspired light leptoquark mediated interactions, over pure SUSY or L-R interactions and perhaps also mirror generated mixings without some sort of quark-lepton unification as its origin.