Modular points and dimensions of Eisenstein deformation spaces

Abstract

In this article, we study two-dimensional Eisenstein deformation spaces, focusing on the Zariski density of modular points and the dimensions of their irreducible components. Over $\mathbb{Q}$, under explicit generic hypotheses, we prove that every irreducible component has characteristic zero and dimension $4$, and that modular points are Zariski dense. Over certain abelian totally real fields, we prove a big $R=\mathbb{T}$ theorem for the union of the high-dimensional components. As an arithmetic application, we establish the irregular Fontaine--Mazur conjecture in the residually reducible, multiplicity-free case for $p\ge 5$, and for $p=3$ outside one explicit local dihedral case. In a complementary direction, we prove a local-to-global finiteness theorem for pseudo-deformation rings. Combining this with ordinary finiteness and modularity-theoretic inputs, we prove Mazur's dimension conjecture over $\mathbb{Q}$ in both the residually reducible and residually irreducible cases, and deduce Emerton's equidimensionality conjecture for the $p$-adic big Hecke algebra for every odd prime.

arXiv comment63 pages. Major change