Hasse principle conjecture for hypersurfaces in products of projective spaces

Let di,nid_i,n_i be positive integers for i{1,,k}i\in\{1,\ldots,k\}, and consider multidegree (d1,,dk)(d_1,\ldots,d_k) hypersurfaces in Pn1××Pnk\mathbb{P}^{n_1}\times\cdots\times\mathbb{P}^{n_k} over Q\mathbb{Q}. A hypersurface is everywhere locally soluble if it has a point over every completion of Q\mathbb{Q}, and is soluble if it has a rational point. Hasse principle conjecture. If di>ni+1d_i>n_i+1 for every ii, then 100%100\% of everywhere locally soluble hypersurfaces fail the Hasse principle. If di<ni+1d_i<n_i+1 for some ii, except when (k,n1,n2,d1,d2)=(2,1,2,2,2)(k,n_1,n_2,d_1,d_2)=(2,1,2,\geq2,2) or (2,2,1,2,2)(2,2,1,2,\geq2), then 100%100\% of everywhere locally soluble hypersurfaces satisfy the Hasse principle, and the proportion of soluble hypersurfaces equals c=νcνc=\prod_\nu c_\nu. The conjecture predicts the typical global behaviour of locally soluble hypersurfaces in products of projective spaces; the stated exceptional cases remain outside its conclusion.

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Primary source

Tom Fisher, Wei Ho and Jennifer Park, “Everywhere local solubility for hypersurfaces in products of projective spaces”, arXiv:1911.09623 (2020).

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