General recursion formula for derivatives of local representation densities

Let qq be the residue-field cardinality, and let AαβγδA_{\alpha\beta\gamma\delta} denote the relevant diagonal hermitian form with α>βγδ0\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)+λ3Aλ00(Aβγδ){A0000(Aαλ00)A0000(Aα(λ2)00)}+(1q2)λκ1Aλκ0(Aβγδ)A1110(Aαλκ0)+(1+q)(1q2)λκμ1Aλκμ(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.

Sources & referencesView supporting material

Primary source

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

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