Finite determinacy of matrices over local rings. Tangent modules to the miniversal deformation for R-linear group actions

Abstract

We consider matrices with entries in a local ring, Mat(m,n,R). Fix a group action, G on Mat(m,n,R), and a subset of allowed deformations, Σ\subseteq Mat(m,n,R). The standard question of Singularity Theory is the finite-(Σ,G)-determinacy of matrices. Finite determinacy implies algebraizability and is equivalent to a stronger notion: stable algebraizability. In our previous work this determinacy question was reduced to the study of the tangent spaces to Σand to the orbit, T_{(Σ,A)}, T_{(GA,A)} , and their quotient, the tangent module to the miniversal deformation. In particular, the order of determinacy is controlled by the annihilator of this tangent module. In this work we study this tangent module for the group action GL(m,R)\times GL(n,R) on Mat(m,n,R) and various natural subgroups of it. We obtain ready-to-use criteria of determinacy for deformations of (embedded) modules, (skew-)symmetric forms, filtered modules, filtered morphisms of filtered modules, chains of modules etc.