Mazur's conjecture on the image of Galois representations of Elliptic curves states that for $N$ large enough there is a unique elliptic curve $E$ over $\mathbb{Q}$ giving rise to a fixed mod $N$ Galois representation $\bar{\rho}: G\_{\mathbb{Q}}\rightarrow GL\_2(\mathbb{Z}/N\mathbb{Z})$.
Is there a similar expectation for normalized Hecke newforms of a fixed weight? In greater detail, let $p$ be a prime, $\bar{\rho}: G\_{\mathbb{Q}}\rightarrow GL\_2(\mathbb{Z}/p\mathbb{Z})$ be a fixed irreducible Galois representation and $k\geq 2$ a fixed integer, is the set of normalized Hecke newforms $f$ with weight $k$ and rational coefficients whose associated residual Galois representation coincides with $\bar{\rho}$ expected to be a finite set when $p$ is large enough? If not, is there a heuristic why it isn't the case?



Is it expected that the mod $p$ representation determines a normalized Hecke newform of fixed weight for p large enough?
This is not true. Take $k=2$, and $p \geq 5$. Let $\ell$ be a prime such that $p$ divides $\ell-1$. Then we know (by Mazur) that there exists a newform of weight $2$ and level $\Gamma\_0(\ell)$ whose residual semi-simple representation is $\overline{\rho} = 1 \oplus \overline{\chi}\_p$ where $\overline{\chi}\_p$ is the modulo $p$ cyclotomic character. The set of such $\ell$ is infinite. Note however that the newform we get almost never have rational coefficients (I think except if $p=5$ and $\ell=11$ in which case $X\_0(11)$ is an elliptic curve).


