Flavor-Changing Top Quark Decays In MSSM Without R-Parity

The flavor changing top quark decays t → cV (V = Z, γ, g) induced by R-parity-violating couplings in the minimal supersymmetric standard model (MSSM) are evaluated. We find that the decays t → cV can be significantly enhanced relative to those in the R-parity conserving SUSY model. Our results show that the top quark FCNC decay can be as large as Br(t → cg) ∼ 10, Br(t → cZ) ∼ 10 and Br(t → cγ) ∼ 10, which are observable at the upgraded Tevatron and the LHC. PACS: 14.65.Ha, 14.80.Ly On leave of absence from Department of Physics, Henan Normal University, China The unexpected large mass of the top quark suggest that it may be more sensitive to new physics than other fermions. In the standard model (SM) the flavor changing neutral current (FCNC) decays of the top quark, t → cV , suppressed by GIM, are found to be far below the detectable levels at current and future colliders [1,2]. So, searching for such FCNC top decays serves as a powerful probe to effects of new physics, which has attracted attentions of both theorists and experimentalists. On the experimental side, the CDF [3,4] and D0 [5] collaborations have reported interesting bounds on these decays [4]. Undoubtedly more stringent bounds will be obtained in the future at the Tevatron upgrade and the LHC. On the theoretical side, a systematic study of the experimental observability for these FCNC top quark decays at the Tevatron and the LHC has been undertaken [6,7]. The results show that the sensitivity on detecting Br(t → cV ) is significant [6,7]: Br(t → cZ) ≃ 4× 10(6× 10), (1) Br(t → cγ) ≃ 4× 10(8× 10), (2) Br(t → cg) ≃ 5× 10(1× 10), (3) at the upgraded Tevatron with an integrated luminosity of 10 (100) fb, and improve several fold, Br(t → cZ) ≃ 8× 10(2× 10), (4) Br(t → cγ) ≃ 2× 10(5× 10). (5) at the LHC with similar integrated luminosities. Despite the interesting experimental possibility indicating in Eqs.(1)-(5), there is so far lacking the demonstration in the minimal supersymmetric model (MSSM), an attractive candidate for physics beyond the standard model, that such limits can be realized. In MSSM with R-parity, the predictions for branching ratios of these FCNC top quark decays were found to be below the above listed detectable levels[8]. In this paper we will show that in the case of R-parity violating MSSM [9, 10] with the existing bounds on the R-parity violating couplings, Br(t → cV ) can reach the detectable level at the upgraded Tevatron and the LHC.