Optimal dimension exponents for coefficient inequalities of unimodular multilinear forms

Let mm be a positive integer, let (r,p)(0,)×(1,](r,p)\in(0,\infty)\times(1,\infty], and let T:pn××pnKT:\ell_p^n\times\cdots\times\ell_p^n\to\mathbb{K} be a unimodular mm-linear form, where nn is a positive integer. The norm T\|T\| is its operator norm. Optimal dimension-exponent conjecture. There is a constant KmK_m such that

(j1,,jm=1nT(ej1,,ejm)r)1rKmnmax{mp+rprpr,0}T for 1<p2,(j1,,jm=1nT(ej1,,ejm)r)1r1.3m0.365nmax{2mr+2mpmprpr2pr,0}T for p2,\left\vert \begin{array}{l} \displaystyle\left( \sum_{j_{1},\ldots,j_{m}=1}^{n}\left\vert T(e_{j_{1}},\ldots,e_{j_{m}})\right\vert ^{r}\right) ^{\frac{1}{r}}\leq K_{m}n^{\max\{\frac{mp+r-pr}{pr},0\}}\left\Vert T\right\Vert\text{ for }1< p\leq2, \\ \displaystyle\left(\sum_{j_{1},\ldots,j_{m}=1}^{n}\left\vert T(e_{j_{1}},\ldots,e_{j_{m}})\right\vert ^{r}\right) ^{\frac{1}{r}}\leq 1.3m^{0.365}n^{\max\{\frac{2mr+2mp-mpr-pr}{2pr},0\}}\left\Vert T\right\Vert\text{ for }p\geq2, \end{array} \right.

and the exponents max{2mr+2mpmprpr2pr,0}\max\{\frac{2mr+2mp-mpr-pr}{2pr},0\} and max{mp+rprpr,0}\max\{\frac{mp+r-pr}{pr},0\} are sharp. This is presented as a consequence that would follow if the preceding conjecture were correct, so its status is conditional and open.

Sources & referencesView supporting material

Primary source

Gustavo Araujo and Daniel Marinho Pellegrino, “A Gale-Berlekamp permutation-switching problem in higher dimensions”, arXiv:1801.09194 (2018).

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