  Let $V_1,V_2,V_3$ be a triple of even dimensional vector spaces over a number
field $F$ equipped with nondegenerate quadratic forms
$\mathcal{Q}_1,\mathcal{Q}_2,\mathcal{Q}_3$, respectively. Let \begin{align*} Y
\subset \prod_{i=1}V_i \end{align*} be the closed subscheme consisting of
$(v_1,v_2,v_3)$ on which
$\mathcal{Q}_1(v_1)=\mathcal{Q}_2(v_2)=\mathcal{Q}_3(v_3)$. Motivated by
conjectures of Braverman and Kazhdan and related work of Lafforgue, Ng\^o, and
Sakellaridis we prove an analogue of the Poisson summation formula for certain
functions on this space.
