General recursion formula for derivatives of local representation densities

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Let qq be the residue-field cardinality, and let AαβγδA_{\alpha\beta\gamma\delta} denote the relevant diagonal hermitian form with α>β≥γ≥δ≥0\alpha>\beta\geq\gamma\geq\delta\geq0. Let A0000′(Aαβγδ)A'_{0000}(A_{\alpha\beta\gamma\delta}) be the derivative quantity and let Aλκμ(Aβγδ)A_{\lambda\kappa\mu}(A_{\beta\gamma\delta}) and A1110(Aαλκμ)A_{1110}(A_{\alpha\lambda\kappa\mu}) be the local representation densities appearing in the formula. The general local-density recursion conjecture. Under these inequalities,

A0000′(Aαβγδ)=A100(Aβγδ)A0000′(Aα100)+∑λ≥3Aλ00(Aβγδ){A0000′(Aαλ00)−A0000′(Aα(λ−2)00)}+(1−q2)∑λ≥κ≥1Aλκ0(Aβγδ)A1110(Aαλκ0)+(1+q)(1−q2)∑λ≥κ≥μ≥1Aλκμ(Aβγδ)A1110(Aαλκμ).\begin{aligned} A'_{0000}(A_{\alpha\beta\gamma\delta})={}&A_{100}(A_{\beta\gamma\delta})A'_{0000}(A_{\alpha100})\\ &+\sum_{\lambda\geq3}A_{\lambda00}(A_{\beta\gamma\delta})\left\{A'_{0000}(A_{\alpha\lambda00})-A'_{0000}(A_{\alpha(\lambda-2)00})\right\}\\ &+(1-q^2)\sum_{\lambda\geq\kappa\geq1}A_{\lambda\kappa0}(A_{\beta\gamma\delta})A_{1110}(A_{\alpha\lambda\kappa0})\\ &+(1+q)(1-q^2)\sum_{\lambda\geq\kappa\geq\mu\geq1}A_{\lambda\kappa\mu}(A_{\beta\gamma\delta})A_{1110}(A_{\alpha\lambda\kappa\mu}). \end{aligned}

The formula is conjectured from the preceding example as a general recursion for local representation densities. Its validity beyond the demonstrated example is not established in the supplied text.

References

Primary source

Sungyoon Cho, “On local representation densities of hermitian forms and special cycles II”, arXiv:2208.00378 (2022).

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