B0-B-bar0 mixing in supergravity models.

Abstract

We consider the supersymmetric contributions to ${B}_{d}^{0}\ensuremath{-}{\overline{B}}_{d}^{0}$ mixing in the supergravity (SUGRA) models, which arise from box diagrams where charginos and up-type squarks or charged Higgs bosons and up-type quarks are exchanged. We have calculated $R$, which is defined to be the ratio between the minimal supersymmetric standard model (MSSM) contributions to ${x}_{d}$ and the standard model one. By choosing a particular set of Cabibbo-Kobayashi-Maskawa parameters allowed by the present data along with the present experimental data on ${x}_{d}$ and $\ensuremath{\epsilon}$, which lead to $0.7\ensuremath{\lesssim}R\ensuremath{\lesssim}1.4$ in the MSSM, we have demonstrated an indication of possible constraints on ${m}_{{\ensuremath{\chi}}_{1}^{\ifmmode\pm\else\textpm\fi{}}}$ and $tan\ensuremath{\beta}$ in the SUGRA models. As a result, for ${m}_{t}({m}_{t})=170$ GeV and $\ensuremath{\mu}>0$, we obtain ${m}_{{\ensuremath{\chi}}_{1}^{\ifmmode\pm\else\textpm\fi{}}}\ensuremath{\gtrsim}112$ GeV for $tan\ensuremath{\beta}=2$ in the no-scale SU(5)\ifmmode\times\else\texttimes\fi{}U(1) SUGRA model and ${m}_{{\ensuremath{\chi}}_{1}^{\ifmmode\pm\else\textpm\fi{}}}\ensuremath{\gtrsim}107(66)$ GeV for $tan\ensuremath{\beta}=2(4)$ in the dilaton SU(5)\ifmmode\times\else\texttimes\fi{}U(1) SUGRA model. In the minimal SU(5) SUGRA model, however, we find no constraint from $R$. It will be very interesting for one to see what values for $R$ the future experimental data would prefer.