The generalized joints bound for flats

Let d1,,drd_1,\dots,d_r and m1,,mrm_1,\dots,m_r be positive integers, put d=d1m1++drmrd=d_1m_1+\cdots+d_rm_r, and let a (d1m1,,drmr)(d_1^{m_1},\dots,d_r^{m_r})-joints configuration (J,F1,,Fk)(\mathcal J,\mathcal F_1,\dots,\mathcal F_k) consist of a family Fi\mathcal F_i of did_i-flats in Fd\mathbb F^d for each i[r]i\in[r], together with joints formed by the intersection of mim_i members of each family, not all lying in a hyperplane. Generalized joints conjecture. For every d=(d1m1,,drmr)\bm d=(d_1^{m_1},\dots,d_r^{m_r}), there is a constant CdC_{\bm d} such that every such configuration satisfies

JCd(F1m1Frmr)1/(m1++mr1).|\mathcal J|\leq C_{\bm d}\bigl(|\mathcal F_1|^{m_1}\cdots|\mathcal F_r|^{m_r}\bigr)^{1/(m_1+\cdots+m_r-1)}.

This would extend the joints and multijoints bounds to mixtures of flats of different dimensions. Over R\mathbb R, the source cites an existing bound with an o(1)o(1) loss, while the stated uniform bound is left open.

Sources & referencesView supporting material

Primary source

Hung-Hsun Hans Yu and Yufei Zhao, “Joints tightened”, arXiv:1911.08605 (2022).

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