Bounds on R - Parity Violating Parameters from Fermion EDM ’ s

We study one-loop contributions to the fermion electric dipole moments in the Minimal Supersymmetric Standard Model with explicit R-parity violating interactions. We obtain new individual bounds on R-parity violating Yukawa couplings and put more stringent limits on certain parameters than those obtained previously. e-mail [email protected] e-mail [email protected] Introduction The Standard Model (SM) of electroweak interactions is constructed in such a way that it automatically conserves both the baryon number B and the lepton flavor number L. These (accidental) global symmetries of the SM result from the particle content and the SU(2)L × U(1)Y gauge invariance of the theory and naturally explain the non-observation of Band L-violating processes, as well as the stability of the nucleon. However, in supersymmetric (SUSY) extensions of the SM these features no longer follow. In fact, by promoting the SM fields to superfields, additional gaugeand Lorentz-invariant terms will be generated which violate B and L conservation. For example, in the SM the Higgs doublet and the lepton doublet have the same SU(2)×U(1) quantum numbers, but the spins of the particles are different; whereas in the SUSY extensions of the SM the distinction between the Higgs doublet and the lepton doublet disappears and one would naturally expect lepton number violation. In order to forbid Band L-violating interactions in SUSY extensions of the SM a parity quantum number defined as R = (−1)3B+L+2S , where S is the spin, is assigned to each component field and invariance under R transformation is imposed [1]. Although the assignment of the ad hoc R-parity to superfields in the SUSY extensions of the SM reproduces the global B and L U(1) symmetries of the SM, it is by no means the only symmetry which allows the construction of phenomenologically viable SUSY extensions of the SM [2]. In fact, from a phenomenological point of view, it is most important to ensure that there are no interaction terms in the Lagrangian which lead to rapid proton decay and, in this respect, other discrete symmetries can be used which are even more effective than R-parity. This is simply due the fact that R-parity only forbids dimension-four Band L-violating operators in the Lagrangian, while dimension-five operators can still remain dangerous, even if suppressed with cut-off’s as large as the Planck mass (see Aulakh et al. in Ref.[1] for an interesting alternative to R-parity which forbids dimension-four and dimensionfive B-violating interactions while allowing L-violating operators of the same dimensions in the Lagrangian). Since there is no fundamental theoretical basis for imposing R-parity conservation on the minimal supersymmetric extension of the Standard Model (MSSM), it is worthwhile to investigate the phenomenological constraints on theoretically allowed R parity breaking couplings in the MSSM. Unlike the SM in which all the elementary matter fields are fermions and, consequently, B