Ratios conjecture for quadratic Dirichlet L-functions over function fields

Let H2g+1\mathcal{H}_{2g+1} be the set of monic square-free polynomials of degree 2g+12g+1 over Fq[x]\mathbb{F}_q[x], and let A={α1,,αk}\mathbf{A}=\{\alpha_1,\ldots,\alpha_k\} and B={β1,,βk}\mathbf{B}=\{\beta_1,\ldots,\beta_k\}. Assume

Reαj<14,1gReβj<14(1jk).|\operatorname{Re}\alpha_j|<\frac14,\qquad \frac1g\ll\operatorname{Re}\beta_j<\frac14\qquad(1\leq j\leq k).

For C={γ1,,γk}\mathbf{C}=\{\gamma_1,\ldots,\gamma_k\}, write C={α:αC}\mathbf{C}^{-}=\{-\alpha:\alpha\in\mathbf{C}\} and q2gC=q2gj=1kγjq^{-2g\mathbf{C}}=q^{-2g\sum_{j=1}^k\gamma_j}, and define SC\mathcal{S}_{\mathbf{C}} by the Euler-product expression in the conjecture below.

Ratios Conjecture. Under these constraints,

1H2g+1DH2g+1j=1kL(1/2+αj,χD)j=1kL(1/2+βj,χD)RAq2gRS(AR)R,\frac{1}{|\mathcal{H}_{2g+1}|}\sum_{D\in\mathcal{H}_{2g+1}}\frac{\prod_{j=1}^kL(1/2+\alpha_j,\chi_D)}{\prod_{j=1}^kL(1/2+\beta_j,\chi_D)}\sim\sum_{\mathbf{R}\subset\mathbf{A}}q^{-2g\mathbf{R}}\mathcal{S}_{(\mathbf{A}\setminus\mathbf{R})\cup\mathbf{R}^{-}},

with some power-saving error term, where

SC=1ijkζq(1+γi+γj)1i<jkζq(1+βi+βj)1i,jkζq(1+βi+γj)\mathcal{S}_{\mathbf{C}}=\frac{\prod_{1\leq i\leq j\leq k}\zeta_q(1+\gamma_i+\gamma_j)\prod_{1\leq i<j\leq k}\zeta_q(1+\beta_i+\beta_j)}{\prod_{1\leq i,j\leq k}\zeta_q(1+\beta_i+\gamma_j)} ×PP1ijk(11P1+γi+γj)1i<jk(11P1+βi+βj)1i,jk(11P1+βi+γj)1\times\prod_{P\in\mathcal{P}}\prod_{1\leq i\leq j\leq k}\left(1-\frac{1}{|P|^{1+\gamma_i+\gamma_j}}\right)\prod_{1\leq i<j\leq k}\left(1-\frac{1}{|P|^{1+\beta_i+\beta_j}}\right)\prod_{1\leq i,j\leq k}\left(1-\frac{1}{|P|^{1+\beta_i+\gamma_j}}\right)^{-1} ×PP(1+(1+1P)1i+j2 evenμB(Pi)τC(Pj)P(i+j)/2).\times\prod_{P\in\mathcal{P}}\left(1+\left(1+\frac{1}{|P|}\right)^{-1}\sum_{i+j\geq2\ \mathrm{even}}\frac{\mu_{\mathbf{B}}(P^i)\tau_{\mathbf{C}}(P^j)}{|P|^{(i+j)/2}}\right).

The conjecture predicts an asymptotic formula for averages of ratios of products of quadratic Dirichlet LL-functions over function fields, extending the ratios-conjecture framework to this family; the paper proves special cases, while the full formula remains conjectural in the stated generality.

Sources & referencesView supporting material

Primary source

Hung M. Bui, Alexandra Florea and Jonathan P. Keating, “The Ratios Conjecture and upper bounds for negative moments of L-functions over function fields”, arXiv:2109.10396 (2021).

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