Coincidence Correspondences and Nonlinear Root Geometry

Abstract

We show that finite morphisms of smooth algebraic varieties naturally give rise to Cartan--Coxeter type structures. Starting from the self-fiber product $X\times_YX$ of a finite morphism $Q:X\to Y$, we construct local symmetry operators and intrinsic Cartan-type invariants from the geometry of its non-diagonal irreducible components. This provides a mechanism for reconstructing root-theoretic structures directly from algebraic correspondences rather than from reflection groups. A central part of the theory is a rank-two geometry associated with pairs of non-diagonal components. We establish a rank-two reduction theorem, derive explicit trace and determinant formulas for the corresponding operators, and obtain a classification into elliptic, parabolic, and hyperbolic transport types. These results yield intrinsic analogues of Cartan matrices, Coxeter transformations, exponents, and Dynkin diagrams associated with finite morphisms. We further prove rigidity theorems showing that the structures arising from a single finite morphism are highly constrained. To obtain richer geometries, we introduce transport atlases of compatible local finite covers equipped with connection data, leading to nonlinear Cartan fields with variable local geometry. This places classical Weyl and complex reflection geometries within a broader correspondence-based root theory extending beyond finite reflection groups.