  We study the short- and long-term effects of an intermediate mass black hole
(IMBH) on the orbits of stars bound to the supermassive black hole (SMBH) at
the center of the Milky Way. A regularized N-body code including post-Newtonian
terms is used to carry out direct integrations of 19 stars in the S-star
cluster for 10 Myr. The mass of the IMBH is assigned one of four values from
400 Msun to 4000 Msun, and its initial semi-major axis with respect to the SMBH
is varied from 0.3-30 mpc, bracketing the radii at which inspiral of the IMBH
is expected to stall. We consider two values for the eccentricity of the
IMBH/SMBH binary, e=(0,0.7), and 12 values for the orientation of the binary's
plane. Changes at the level of 1% in the orbital elements of the S-stars could
occur in just a few years if the IMBH is sufficiently massive. On time scales
of 1 Myr or longer, the IMBH efficiently randomizes the eccentricities and
orbital inclinations of the S-stars. Kozai oscillations are observed when the
IMBH lies well outside the orbits of the stars. Perturbations from the IMBH can
eject stars from the cluster, producing hypervelocity stars, and can also
scatter stars into the SMBH; stars with high initial eccentricities are most
likely to be affected in both cases. The distribution of S-star orbital
elements is significantly altered from its currently-observed form by IMBHs
with masses greater than 1000 Msun if the IMBH/SMBH semi-major axis lies in the
range 3-10 mpc. We use these results to further constrain the allowed
parameters of an IMBH/SMBH binary at the Galactic center.
