  We present a study of the effect of bulge mass on the evolution of bar
pattern speed in isolated disk galaxies using N-body simulations. Earlier
studies have shown that disk stars at the inner resonances can transfer a
significant amount of angular momentum to the dark matter halo and this results
in the slow down of the bar pattern speed. In this paper we investigate how the
mass of the other spheroidal component, the bulge, affects bar pattern speeds.
In our galaxy models the initial bars are all rotating fast as the R parameter,
which is the ratio of the corotation radius to bar radius is less than 1.4,
which is typical of fast bars. However, as the galaxies evolve with time, the
bar pattern speed (${\Omega}_p$ ) slows down leading to R $>$1.4 for all the
models except for the model with the most massive bulge, in which the bar
formed late and did not have time to evolve. The rapid slowdown of ${\Omega}_p$
is due to the larger angular momentum transfer from the disk to the bulge, and
is due to interactions between stars at the inner resonances and those in the
bar. Hence we conclude that the decrease in ${\Omega}_p$ clearly depends on
bulge mass in barred galaxies and decreases faster for galaxies with more
massive bulges. We discuss the implications of our results for observations of
bar pattern speeds in galaxies.
