μ -ordinary Hasse invariants and the canonical filtration of a p-divisible group.
Abstract: In his 1973 paper, Katz constructed overconvergent modular forms on the modular curve geometrically, using the Hasse invariant and Lubin’s Theorem on the canonical subgroup of an elliptic curve. Many improvements have since been made on these constructions on many Shimura varieties, but this approach is now well known only when the ordinary locus is non-empty. I will try to explain how to get rid of this assumption, and detail the construction of a replacement for the Hasse invariant and the construction of the canonical filtration focusing on the local analogue of the Picard modular surface.