Non-splitting Flags, Iterated Circuits, σ̲ -Matrices and Cayley Configurations

Abstract

We explore four approaches to the question of defectivity for a complex projective toric variety XA associated with an integral configuration A. The explicit tropicalization of the dual variety XA∨ due to Dickenstein, Feichtner, and Sturmfels allows for the computation of the defect in terms of an affine combinatorial invariant ρ(A). We express ρ(A) in terms of affine invariants ι(A) associated to Esterov’s iterated circuits and λ(A), an invariant defined by Curran and Cattani in terms of a Gale dual of A. Thus we obtain formulae for the dual defect in terms of iterated circuits and Gale duals. An alternative expression for the dual defect of XA is given by Furukawa–Ito in terms of Cayley decompositions of A. We give a Gale dual interpretation of these decompositions and apply it to the study of defective configurations.