  We analyse a set of collisionless disc galaxy simulations to study the
consequences of bar formation and evolution on the M-sigma relation of
supermassive black holes. The redistribution of angular momentum driven by bars
leads to a mass increase within the central region, raising the velocity
dispersion of the bulge, sigma, on average by ~12% and as much as ~20%. If a
disc galaxy with a SMBH satisfying the M-sigma relation forms a bar, and the
SMBH does not grow in the process, then the increase in sigma moves the galaxy
off the M-sigma relation. We explore various effects that can affect this
result including contamination from the disc and anisotropy. The displacement
from the M-sigma relation for individual model barred galaxies correlates with
both M(B)/M(B+D) and beta_phi(B+D) measured within the effective radius of the
bulge. Overall, this process leads to an M-sigma for barred galaxies offset
from that of unbarred galaxies, as well as an increase in its scatter. We
assemble samples of unbarred and barred galaxies with classical bulges and find
tentative hints of an offset between the two consistent with the predicted.
Including all barred galaxies, rather than just those with a classical bulge,
leads to a significantly larger offset.
