Non-optimal levels of some reducible mod $p$ modular representations

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1. Verfasser: Deo, Shaunak V.
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Veröffentlicht: 2022
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author Deo, Shaunak V.
author_facet Deo, Shaunak V.
contents Let $p \geq 5$ be a prime, $N$ be an integer not divisible by $p$, $\barρ_0$ be a reducible, odd and semi-simple representation of $G_{\mathbb{Q},Np}$ of dimension $2$ and $\{\ell_1,\cdots,\ell_r\}$ be a set of primes not dividing $Np$. After assuming that a certain Selmer group has dimension at most $1$, we find sufficient conditions for the existence of a cuspidal eigenform $f$ of level $N\prod_{i=1}^{r}\ell_i$ and appropriate weight lifting $\barρ_0$ such that $f$ is new at every $\ell_i$. Moreover, suppose $p \mid \ell_{i_0}+1$ for some $1 \leq i_0 \leq r$. Then, after assuming that a certain Selmer group vanishes, we find sufficient conditions for the existence of a cuspidal eigenform of level $N\ell_{i_0}^2 \prod_{j \neq i_0} \ell_j$ and appropriate weight which is new at every $\ell_i$ and which lifts $\barρ_0$. As a consequence, we prove a conjecture of Billerey--Menares in many cases.
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id arxiv_https___arxiv_org_abs_2206_06209
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publishDate 2022
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spellingShingle Non-optimal levels of some reducible mod $p$ modular representations
Deo, Shaunak V.
Number Theory
11F33, 11F80 (Primary)
Let $p \geq 5$ be a prime, $N$ be an integer not divisible by $p$, $\barρ_0$ be a reducible, odd and semi-simple representation of $G_{\mathbb{Q},Np}$ of dimension $2$ and $\{\ell_1,\cdots,\ell_r\}$ be a set of primes not dividing $Np$. After assuming that a certain Selmer group has dimension at most $1$, we find sufficient conditions for the existence of a cuspidal eigenform $f$ of level $N\prod_{i=1}^{r}\ell_i$ and appropriate weight lifting $\barρ_0$ such that $f$ is new at every $\ell_i$. Moreover, suppose $p \mid \ell_{i_0}+1$ for some $1 \leq i_0 \leq r$. Then, after assuming that a certain Selmer group vanishes, we find sufficient conditions for the existence of a cuspidal eigenform of level $N\ell_{i_0}^2 \prod_{j \neq i_0} \ell_j$ and appropriate weight which is new at every $\ell_i$ and which lifts $\barρ_0$. As a consequence, we prove a conjecture of Billerey--Menares in many cases.
title Non-optimal levels of some reducible mod $p$ modular representations
topic Number Theory
11F33, 11F80 (Primary)
url https://arxiv.org/abs/2206.06209