Triple-indexed Gaussian supremum conjecture

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Let p≥1p\geq 1, let n,mn,m be positive integers, let (aijk)i,j≤n,k≤m(a_{ijk})_{i,j\leq n,k\leq m} be a triple-indexed real matrix, let T⊂RmT\subset\mathbb R^m be bounded and nonempty, and let gig_i and gj′g'_j be independent standard Gaussian random variables. Write CC for a universal constant. Triple-indexed Gaussian supremum conjecture. One has

Esup⁡∥x∥2≤1, t∈T∣∑ijkaijkgixjtk∣≤C(1pEsup⁡t∈T∣∑ijkaijkgigj′tk∣+sup⁡∥x∥2≤1Esup⁡t∈T∣∑ijkaijkgixjtk∣+sup⁡t∈T(∑ij(∑kaijktk)2)1/2+psup⁡∥x∥2≤1, t∈T(∑i(∑jkaijxjtk)2)1/2).\begin{aligned} \mathbb E\sup_{\|x\|_2\leq 1,\,t\in T}\left|\sum_{ijk}a_{ijk}g_ix_jt_k\right|\leq C\Bigg(&\frac{1}{\sqrt p}\mathbb E\sup_{t\in T}\left|\sum_{ijk}a_{ijk}g_ig'_jt_k\right|\\ &+\sup_{\|x\|_2\leq1}\mathbb E\sup_{t\in T}\left|\sum_{ijk}a_{ijk}g_ix_jt_k\right|+\sup_{t\in T}\left(\sum_{ij}\left(\sum_k a_{ijk}t_k\right)^2\right)^{1/2}\\ &+\sqrt p\sup_{\|x\|_2\leq1,\,t\in T}\left(\sum_i\left(\sum_{jk}a_{ij}x_jt_k\right)^2\right)^{1/2}\Bigg). \end{aligned}

This is the reformulation of the preceding Banach-space conjecture in finite-dimensional tensor coordinates, with TT representing a bounded nonempty subset of the coefficient space. The supplied source does not give evidence that the conjecture has been resolved.

References

Primary source

Radosław Adamczak, Rafał Latała and Rafał Meller, “Hanson-Wright inequality in Banach spaces”, arXiv:1811.00353 (2020).

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