Evans's conjectural hypergeometric relation for weight-two newforms

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Let a3(n)a_3(n) and a4(n)a_4(n) be the Fourier coefficients of newforms

∑n≥1a3(n)qn∈S2(Γ0(972)),∑n≥1a4(n)qn∈S2(Γ0(768)),\sum_{n\geq1}a_3(n)q^n\in S_2\left(\Gamma_0(972)\right),\qquad \sum_{n\geq1}a_4(n)q^n\in S_2\left(\Gamma_0(768)\right),

whose coefficient fields are Q(2)\mathbb{Q}\left(\sqrt{2}\right) and Q(3)\mathbb{Q}\left(\sqrt{3}\right), respectively. Let χ6\chi_6 and χ8\chi_8 denote the relevant characters of orders 66 and 88, let φ\varphi be the quadratic character, let JJ denote a Jacobi sum, and let 3F2(⋯ )q{}_3F_2(\cdots)_q denote the finite-field hypergeometric value. Evans's conjecture. If q≡1(mod6)q\equiv1\pmod{6}, then

χ6‾(12)J(χ6,χ6)−χ6‾(3)J(χ62,χ62)⋅3F2(χ6‾,φ,χ6φχ6,φχ6∣14)q={a3(p),q=p, p≡1(mod6),a3(p)2+2p,q=p2, p≡5(mod6),\overline{\chi_6}(12)J\left(\chi_6,\chi_6\right)-\overline{\chi_6}(3)J\left(\chi_6^2,\chi_6^2\right)\cdot {}_3F_2\left(\begin{array}{ccc}\overline{\chi_6},&\varphi,&\chi_6\\&\varphi\chi_6,&\varphi\chi_6\end{array}\Big|\frac14\right)_q=\begin{cases}a_3(p),&q=p,\ p\equiv1\pmod{6},\\a_3(p)^2+2p,&q=p^2,\ p\equiv5\pmod{6},\end{cases}

and if q≡1(mod8)q\equiv1\pmod{8}, then

χ8(−4)J(χ8,χ8)−χ8(−4)J(χ82,χ83)⋅3F2(χ8‾,χ83,χ8χ8‾2,φχ8∣14)q={a4(p),q=p, p≡1(mod8),a4(p)2+2p2,q=p2, p≢1(mod8).\chi_8(-4)J\left(\chi_8,\chi_8\right)-\chi_8(-4)J\left(\chi_8^2,\chi_8^3\right)\cdot {}_3F_2\left(\begin{array}{ccc}\overline{\chi_8},&\chi_8^3,&\chi_8\\&\overline{\chi_8}^2,&\varphi\chi_8\end{array}\Big|\frac14\right)_q=\begin{cases}a_4(p),&q=p,\ p\equiv1\pmod{8},\\a_4(p)^2+2p^2,&q=p^2,\ p\not\equiv1\pmod{8}.\end{cases}

These are conjectural relations connecting Fourier coefficients of weight-two newforms with non-integral coefficient fields to finite-field hypergeometric functions; the supplied text gives no resolution status.

References

Primary source

Madeline Locus Dawsey and Dermot McCarthy, “Hypergeometric Functions over Finite Fields and Modular Forms: A Survey and New Conjectures”, arXiv:2101.06303 (2021).

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