Gap-vector conjecture for Veronese embeddings

Let X=vd(Pn)X=v_d(\mathbb P^n) be the ddth Veronese embedding of projective nn-space, and define

jˉ:=min{j:gj(X)>0}.\bar j:=\min\{j:g_j(X)>0\}.

Here gj(X)g_j(X) denotes the jjth component of the gap vector of XX, and codimX\operatorname{codim}X denotes the codimension of XX. Gap-vector conjecture. The first nonzero component occurs at

jˉ=(n+dd)(n+1)+12(n+12)2+2(n+2d2d)2(n+1)(n+dd),\bar j=\left\lceil\binom{n+d}{d}-(n+1)+\frac{1}{2}-\sqrt{\left(n+\frac{1}{2}\right)^2+2\binom{n+2d}{2d}-2(n+1)\binom{n+d}{d}}\right\rceil,

and, for jˉjcodimX\bar j\leq j\leq\operatorname{codim}X, one has

gj(X)=(n+2d2d)j(n+1)((n+dd)j+12).g_j(X)=\binom{n+2d}{2d}-j(n+1)-\binom{\binom{n+d}{d}-j+1}{2}.

The conjecture asserts that the bounds previously established for the smallest index with positive gap are sharp, while also determining all subsequent components of the gap vector through codimension.

Sources & referencesView supporting material

Primary source

Grigoriy Blekherman, Sadik Iliman, Martina Juhnke-Kubitzke and Mauricio Velasco, “Gap vectors of real projective varieties”, arXiv:1407.0585 (2014).

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