Gap-vector conjecture for Veronese embeddings

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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 codim⁡X\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 jˉ≤j≤codim⁡X\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.

References

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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