Local to global principle in circle packings

One of the most spectacular results on arithmetic of Apollonian circle packings is the“almost” local to global principle for curvatures in any given integral Apollonian packing as described by Bourgain-Kontorovichin 2014. The methods in their work, inspired originally by an observation of Sarnak’s in his letter to Lagarias on Apollonian circle packings, apply to a much larger class of circle packings. In this talk, we clarify what “almost” local to global means, and describe what the larger class is, as well as what aspects of the packings in this class seem necessary in order to conclude an “almost” local to global result and how they enter the proof. This is joint work with Fuchs and Stange.