2011/11/15 by Andrew Snowden, Snowden, Andrew
Mathematics · #Algebraic Geometry and Number Theory #Algebraic structures and combinatorial models #Commutative Algebra and Its Applications #FOS: Mathematics #Number Theory (math.NT)
paper · pdf · doi:10.48550/arxiv.1111.3654
openalex publication_date 2011/11/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Let Runiv be the universal deformation ring of a residual representation of a local Galois group. Kisin showed that many loci in MaxSpec(Runiv[1/p]) of interest are Zariski closed, and gave a way to study the generic fiber of the corresponding quotient of Runiv. However, his method gives little information about the quotient ring before inverting p. We give a method for studying this quotient in certain cases, and carry it out in the simplest non-trivial case. Precisely, suppose that V0 is the trivial two dimensional representation and let R be the unique Zp-flat and reduced quotient of Runiv such that MaxSpec(R[1/p]) consists of ordinary representations with Hodge--Tate weights 0 and 1. We describe the functor of points of (a slightly modified version of) R and show that the irreducile components of Spec(R) are normal, Cohen--Macaulay and not Gorenstein. This has two well-known applications to global deformation rings: first, a global deformation ring employing these local conditions is torsion-free; and second, Kisin's R[1/p]=T[1/p] theorem can be upgraded in this setting to an R=T theorem.