  We perform several high resolution N-Body/SPH simulations of low surface
brightness galaxies (LSBs) embedded in cold dark matter halos to study how
likely is bar formation in such systems. The behavior of various collisionless
galaxy models is studied both in isolation and in the presence of a large
perturbing satellite. We also consider models with a dominant gaseous component
in the disk. We find that in general bar formation requires disk masses at
least a factor of 2 higher than those inferred for LSBs under the assumption of
a normal stellar mass-to-light ratio. Low surface density stellar disks
contributing less than 10% of the total virial mass are stable within NFW halos
spanning a range of concentrations. However, a purely gaseous disk can form a
bar even for quite low masses and for realistic temperatures provided that
cooling is very efficient (we adopt an isothermal equation of state) and that
the halo has a very low concentration, c < 5. The bars that form in these LSB
models are shorter than the typical halo scale radius - their overall angular
momentum content might be too low to affect significantly the inner dark halo
structure. Once formed, all the bars evolve into bulge-like structures in a few
Gyr and can excite spiral patterns in the surrounding disk component. The
recently discovered red LSBs show significant non-axisymmetric structure and
bulge-like components and share many of their structural properties with the
final states of our LSB models with massive disks. Our results imply that a
bulge-like component must be present in any low surface brightness galaxy that
ever went bar unstable in the past.
