Determination of certain mod $p$ Galois representations using local constancy

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Hauptverfasser: Ganguli, Abhik, Kumar, Suneel
Format: Preprint
Veröffentlicht: 2024
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author Ganguli, Abhik
Kumar, Suneel
author_facet Ganguli, Abhik
Kumar, Suneel
contents Let $p \geq 5$ be a prime. Let $k = b + c(p-1)$ be an integer in $[2p+2, p^2 - p +3]$, where $b \in [2,p]$ and $c \in [2, p-1]$. We prove local constancy in the weight space of the mod $p$ reduction of certain two-dimensional crystalline representations of $\mathrm{Gal}(\bar{\mathbb{Q}}_p/\mathbb{Q}_p)$, where the slope $ν(a_p)$ is constrained to be in $(1, c)$ and non-integral. We use the mod $p$ local Langlands correspondence for $\text{GL}_{2} (\mathbb{Q}_{p})$ to compute the mod $p$ reductions explicitly, thereby also giving a lower bound on the radius of constancy around the weights $k$ in the above range and under additional conditions on the slope. As an application of local constancy, we obtain explicit mod $p$ reductions at many new values of $k$ and $a_p$.
format Preprint
id arxiv_https___arxiv_org_abs_2406_15600
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle Determination of certain mod $p$ Galois representations using local constancy
Ganguli, Abhik
Kumar, Suneel
Number Theory
11F80, 11F70, 11F33
Let $p \geq 5$ be a prime. Let $k = b + c(p-1)$ be an integer in $[2p+2, p^2 - p +3]$, where $b \in [2,p]$ and $c \in [2, p-1]$. We prove local constancy in the weight space of the mod $p$ reduction of certain two-dimensional crystalline representations of $\mathrm{Gal}(\bar{\mathbb{Q}}_p/\mathbb{Q}_p)$, where the slope $ν(a_p)$ is constrained to be in $(1, c)$ and non-integral. We use the mod $p$ local Langlands correspondence for $\text{GL}_{2} (\mathbb{Q}_{p})$ to compute the mod $p$ reductions explicitly, thereby also giving a lower bound on the radius of constancy around the weights $k$ in the above range and under additional conditions on the slope. As an application of local constancy, we obtain explicit mod $p$ reductions at many new values of $k$ and $a_p$.
title Determination of certain mod $p$ Galois representations using local constancy
topic Number Theory
11F80, 11F70, 11F33
url https://arxiv.org/abs/2406.15600