Arithmetic biquadratic fundamental lemma

Let FF be the base local field, let K/K3K/K_3 be unramified, and let

Φ0:K0M2h(F),Φ1:K1M2h(F),Φ2:K2M2h(F),Φ3:K3M2h(F)\Phi_0:K_0\to M_{2h}(F),\quad \Phi_1:K_1\to M_{2h}(F),\quad \Phi_2:K_2\to M_{2h}(F),\quad \Phi_3:K_3\to M_{2h}(F)

be embeddings such that (Φ1,Φ2)(\Phi_1,\Phi_2) is a regular semisimple pair and (Φ0,Φ3)(\Phi_0,\Phi_3) is regular semisimple and matching. Let XX be the Lubin–Tate formal scheme and Y1,Y2Y_1,Y_2 the formal schemes of formal OKi\mathcal O_{K_i}-modules, with closed immersions fi:YiXf_i:Y_i\to X, and let 1\mathbf 1 be the characteristic function of GL2h(OF)\mathrm{GL}_{2h}(\mathcal O_F). Arithmetic biquadratic fundamental lemma. One has

±1log(q2)ddsO(Φ0,Φ3)(1;s,η)s=0=lenWH0(X,f1OY1OXf2OY1).\frac{\pm1}{\log(q^2)}\left.\frac{d}{ds}O_{(\Phi_0,\Phi_3)}(\mathbf 1;s,\eta)\right|_{s=0}=\operatorname{len}_W H^0\left(X,f_{1*}\mathcal O_{Y_1}\otimes_{\mathcal O_X}f_{2*}\mathcal O_{Y_1}\right).

This is the arithmetic, or central-derivative, counterpart of the biquadratic fundamental lemma: the derivative of the vanishing central orbital integral is related to an intersection length on Lubin–Tate space.

Sources & referencesView supporting material

Primary source

Benjamin Howard and Qirui Li, “Intersections in Lubin-Tate space and biquadratic fundamental lemmas”, arXiv:2010.07365 (2024).

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