The non-CM Fourier coefficient conjecture for odd discriminant level

Let kk be an integer with k3k\geq 3, and let D=p1pD=p_1\cdots p_\ell be an odd discriminant. Let SkEll(Γ1(D),ωE/Q)S_k^{\mathrm{Ell}}(\Gamma_1(D),\omega_{E/\mathbb{Q}}) denote the space of elliptic cusp forms of weight kk, level Γ1(D)\Gamma_1(D), and nebentypus ωE/Q\omega_{E/\mathbb{Q}}. A normalized newform in this space is non-CM if it does not have complex multiplication. The non-CM Fourier coefficient conjecture. If this space contains a non-CM normalized newform, then at least one such newform ff satisfies

af(pi)±pi(k1)/2for every i.a_f(p_i)\neq \pm p_i^{(k-1)/2}\quad\text{for every }i.

Here af(pi)a_f(p_i) is the pip_i-th Fourier coefficient of ff. This conjecture asserts that, among the available non-CM newforms, one can find a form avoiding the CM-type extremal values at every prime dividing the odd discriminant. The source provides no resolution, so the conjecture is recorded as open.

Sources & referencesView supporting material

Primary source

Shuji Horinaga, Yota Maeda and Takuya Yamauchi, “The Kodaira dimension of even-dimensional ball quotients”, arXiv:2507.22203 (2025).

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