Topology of the SU(2) vacuum: a lattice study using improved cooling

We study the topological structure of the SU(2) vacuum at zero temperature: topological susceptibility, size, shape and distance distributions of the instantons. We use a cooling algorithm based on an improved action with scale invariant instanton solutions. This algorithm needs no monitoring or calibration, has an inherent cut off for dislocations and leaves unchanged instantons at physical scales. The physical relevance of our results is checked by studying the scaling and finite volume dependence. We obtain a susceptibility of (200(15) MeV)4. The instanton size distribution is peaked around 0.43 fm, and the distance distribution indicates a homogeneous, random spatial structure. (orig.)