On fixed point sets and Lefschetz modules for sporadic simple groups

We consider 2-local geometries and other subgroup complexes for sporadic simple groups. For six groups, the fixed point set of a noncentral involution is shown to be equivariantly homotopy equivalent to a standard geometry for the component of the centralizer. For odd primes, fixed point sets are computed for sporadic groups having an extraspecial Sylow pp-subgroup of order p3p3, acting on the complex of those pp-radical subgroups containing a pp-central element in their centers. Vertices for summands of the associated reduced Lefschetz modules are described.