| In the fist part of the talk I will focus on the cluster size statistics in systems of self-propelled particles (SPPs) without cohesion. I will argue that SPP systems exhibit two phases: i) a mono-disperse phase where the cluster size distribution is dominated by an exponential tail, and ii) an aggregated phase characterized by the presence of non-monotonic cluster size distributions with a peak at large cluster sizes. At the transition between these two phases, the CSD is a power-law with a critical exponent. This transition can be used as a criterion to determine the onset of collective phenomena in SPP systems. Such criterion is particularly useful in experimental SPP system where global orientational order is often not observed. In the second part of the talk I will present some recently obtained results for SPPs in the presence of obstacles. I will show that these systems exhibit a non trivial behavior as new obstacles are added into the system. |
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