The $m=2$ amplituhedron is a positive geometry

Abstract

Amplituhedra are semi-algebraic sets of fundamental importance in particle physics. Their discovery initiated the field of Positive Geometry. We settle a central conjecture in this field: we show that the $m=2$ amplituhedron is a positive geometry. Our main new tool is a Hodge-theoretic criterion for being a positive geometry, connecting the work of Brown--Dupont with the original setup of Arkani-Hamed--Bai--Lam.