  We present a detailed and complete calculation of the loop corrections to the
mass difference $\Delta m_{B_d^0}/m_{B_d^0}$. We include charginos and scalar
up quarks as well as gluinos and scalar down quarks on the relevant loop
diagrams. We include the mixings of the charginos and of the scalar partners of
the left and right handed quarks. We find that the gluino contribution to this
quantity is important with respect to the chargino contribution only in a small
part of phase space: mainly when the gluino mass is small ($\sim$ 100 GeV) and
the symmetry-breaking parameter $m_S$ is below 300 GeV. This contribution is
also important for very large values of $\tan\beta$ ($\sim$ 50) irrespective of
the other parameters. Otherwise, the chargino contribution dominates vastly and
can be roughly as large as that of the Standard Model. We also present the
contribution of the charged Higgs to the mass difference $\Delta
m_{B_d^0}/m_{B_d^0}$\ in the case $m_b\tan\beta\ll m_t\cot\beta$. This last
contribution can be larger than the Standard Model contribution for small
values of the Higgs mass and small values of $\tan\beta$.

High Energy Physics - Phenomenology