{ital B}{sup 0}-{ital {bar B}}{sup 0} mixing in supergravity models

We consider the supersymmetric contributions to {ital B}{sup 0}{sub {ital d}}-{ital {bar B}}{sup 0}{sub {ital d}} 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 {ital R}, which is defined to be the ratio between the minimal supersymmetric standard model (MSSM) contributions to {ital x}{sub {ital 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 {ital x}{sub {ital d}} and {epsilon}, which lead to 0.7{approx_lt}{ital R}{approx_lt}1.4 in the MSSM, we have demonstrated an indication of possible constraints on {ital m}{sub {chi}{sub 1}{sup {plus_minus}}} and tan{beta} in the SUGRA models. As a result, for {ital m}{sub {ital t}}({ital m}{sub {ital t}})=170 GeV and {mu}{gt}0, we obtain {ital m}{sub {chi}{sub 1}{sup {plus_minus}}}{approx_gt}112 GeV for tan{beta}=2 in the no-scale SU(5){times}U(1) SUGRA model and {ital m}{sub {chi}{sub 1}{sup {plus_minus}}}{approx_gt}107(66) GeV for tan{beta}=2(4) in the dilaton SU(5){times}U(1) SUGRA model. In the minimal SU(5) SUGRA model, however, we find no constraint from {ital R}. It will be very interesting for one to see what values for {ital R} the futuremore » experimental data would prefer. {copyright} {ital 1996 The American Physical Society.}« less