On the structure of locally potentially equivalent Galois representations

TL;DR

This paper classifies pairs of $ ext{ell}$-adic Galois representations that are locally potentially equivalent under certain conditions, revealing they are essentially trivial or abelian after twisting, and establishes criteria for their potential equivalence.

Contribution

It provides a classification of locally potentially equivalent Galois representations with connected monodromy groups, identifying when they are globally potentially equivalent under specific conditions.

Findings

Classified pairs of locally potentially equivalent Galois representations.

Showed conditions under which such representations are globally potentially equivalent.

Identified that one representation can be trivial or abelian after twisting.

Abstract

Suppose $\rho_1, \rho_2$ are two $\ell$-adic Galois representations of the absolute Galois group of a number field, such that the algebraic monodromy group of one of the representations is connected and the representations are locally potentially equivalent at a set of places of positive upper density. We classify such pairs of representations and show that up to twisting by some representation, it is given by a pair of representations one of which is trivial and the other abelian. Consequently, assuming that the first representation has connected algebraic monodromy group, we obtain that the representations are potentially equivalent, provided one of the following conditions hold: (a) the first representation is absolutely irreducible; (b) the ranks of the algebraic monodromy groups are equal; (c) the algebraic monodromy group of the second representation is also connected and (d) the commutant of the image of the second representation remains the same upon restriction to subgroups of finite index of the Galois group.