Title: T-Branes at the Limits of Geometry,
Abstract: Singular limits of 6D F-theory compactifications are often captured by
T-branes, namely a non-abelian configuration of intersecting 7-branes with a
nilpotent matrix of normal deformations. The long distance approximation of
such 7-branes is a Hitchin-like system in which simple and irregular poles
emerge at marked points of the geometry. When multiple matter fields localize
at the same point in the geometry, the associated Higgs field can exhibit
irregular behavior, namely poles of order greater than one. This provides a
geometric mechanism to engineer wild Higgs bundles. Physical constraints such
as anomaly cancellation and consistent coupling to gravity also limit the order
of such poles. Using this geometric formulation, we unify seemingly different
wild Hitchin systems in a single framework in which orders of poles become
adjustable parameters dictated by tuning gauge singlet moduli of the F-theory
model.