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Joints of Varieties

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Tidor, J 
Yu, HHH 
Zhao, Y 


jats:titleAbstract</jats:title>jats:pWe generalize the Guth–Katz joints theorem from lines to varieties. A special case says that jats:italicN</jats:italic> planes (2-flats) in 6 dimensions (over any field) have jats:inline-formulajats:alternativesjats:tex-math$$O(N^{3/2})$$</jats:tex-math><mml:math xmlns:mml=""> mml:mrow mml:miO</mml:mi> mml:mo(</mml:mo> mml:msup mml:miN</mml:mi> mml:mrow mml:mn3</mml:mn> mml:mo/</mml:mo> mml:mn2</mml:mn> </mml:mrow> </mml:msup> mml:mo)</mml:mo> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> joints, where a joint is a point contained in a triple of these planes not all lying in some hyperplane. More generally, we prove the same bound when the set of jats:italicN</jats:italic> planes is replaced by a set of 2-dimensional algebraic varieties of total degree jats:italicN</jats:italic>, and a joint is a point that is regular for three varieties whose tangent planes at that point are not all contained in some hyperplane. Our most general result gives upper bounds, tight up to constant factors, for joints with multiplicities for several sets of varieties of arbitrary dimensions (known as Carbery’s conjecture). Our main innovation is a new way to extend the polynomial method to higher dimensional objects, relating the degree of a polynomial and its orders of vanishing on a given set of points on a variety.</jats:p>


Funder: Massachusetts Institute of Technology (MIT)


4901 Applied Mathematics, 4904 Pure Mathematics, 49 Mathematical Sciences

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Geometric and Functional Analysis

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Springer Science and Business Media LLC