  We study the effect of flexibility and bend angle on systems of hard
semiflexible boomerangs. These are modelled as two rodlike segments joined at
one end with an angle that can fluctuate about a preferred angle. We use a
second-virial theory for semiflexible chains with two segments, and numerically
solve for the full orientation distribution function as a function of the four
angles that determine the boomerang's orientation. We plot the single segment
distributions as a function of two angles as well as the interarm angle
distribution. For stiff boomerangs, we find prolate, oblate, and biaxial
nematic phases depending on the bend angle and density, in partial agreement
with previous results on rigid boomerangs. For the case that the preferred
interarm angle is $90^\circ$, however, we find that the biaxial nematic phase
has four-fold rather than two-fold rotational symmetry, and thus requires
fourth-rank order parameters to describe it. In addition, we find that
flexibility drastically reduces the region of stability for the biaxial nematic
phase, with the prolate nematic becoming more favourable.
