The codimension-two spin-genus representation conjecture for quadratic forms

Let q:ZmZq:\mathbb{Z}^m\to\mathbb{Z} and Q:ZnZQ:\mathbb{Z}^n\to\mathbb{Z} be integral quadratic forms with m<nm<n, and let

min(q):=minxZm{0}q(x).\min(q):=\min_{x\in\mathbb{Z}^m\setminus\{0\}}q(x).

Assume that qq is primitively represented by an element of the spin genus of QQ, and that nm=2n-m=2. Codimension-two spin-genus representation conjecture. There exists a constant C(Q)>0C(Q)>0 such that

min(q)C(Q)\min(q)\geq C(Q)

implies that qq is primitively represented by QQ. The local representation and minimum conditions are insufficient in codimension two because of spinor obstructions; the conjecture addresses whether the spin-genus condition becomes sufficient for sufficiently large minimum. Its m=1m=1 case, concerning primitive representations of integers, has been established by Duke and Schulze-Pillot using estimates for Fourier coefficients of half-integral-weight forms, so the general statement is resolved only in that special case.

Sources & referencesView supporting material

Primary source

Wooyeon Kim, Andreas Wieser and Pengyu Yang, “Representations of binary quadratic forms by quaternary quadratic forms”, arXiv:2604.19437 (2026).

Additional references

2 papers in this index state this conjecture (2025–2026). The statement above is taken from the most recent of them; the others are arXiv:2511.22877.

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