  Disc non-axisymmetrc components, such as spirals and central bars, are
nowadays known to play an important role in shaping galactic discs. Here we use
Tree-SPH N-body simulations to examine the effect of these perturbers on two
aspects: the occurrence of multiple patterns in discs and the effects of radial
migration on disc thickening. We find that, in addition to a central bar,
multiple spiral patterns and lopsided modes develop in all models. Interaction
among these asymmetric features results in a large scale stellar migration.
However, we show that, despite the strong radial mixing, discs cannot be
thickened sufficiently to match observed thick discs. We relate this to the
adiabatic cooling as stars migrate radially outwards. We also find that the
bulge contribution to a thick-disc component for an Sa-type galaxy at ~2.5 disc
scale-lengths is less than 1% and zero in the case of a Milky Way-like,
Sb-type. Our findings cast doubt on the plausibility of thick disc formation
via stellar radial migration.
