Vector-valued Maclaurin inequality

Fix vectors v1,,vmRdv_1,\dots,v_m\in\mathbb{R}^d with 1dm1\le d\le m. For integers kk satisfying 2kd2\le k\le d, let vi1vik|v_{i_1}\wedge\cdots\wedge v_{i_k}| denote the Euclidean norm of the exterior product. Vector-valued Maclaurin inequality. For every p[0,]p\in[0,\infty], one has

(1i1<<ikmvi1vikp(mk))1kp(1i1<<ik1mvi1vik1p(mk1))1(k1)p,\left(\frac{\sum\limits_{1\le i_1<\cdots<i_k\le m}|v_{i_1}\wedge\cdots\wedge v_{i_k}|^p}{\binom{m}{k}}\right)^{\frac{1}{kp}} \le \left(\frac{\sum\limits_{1\le i_1<\cdots<i_{k-1}\le m}|v_{i_1}\wedge\cdots\wedge v_{i_{k-1}}|^p}{\binom{m}{k-1}}\right)^{\frac{1}{(k-1)p}},

with equality if and only if m=dm=d and the vectors viv_i form an orthonormal basis. Here the cases p=0p=0 and p=p=\infty are understood through the corresponding limiting interpretations of the displayed expression. Earlier results establish the inequality for p=1p=1 in several cases, including k=2,3,dk=2,3,d in all dimensions when m=dm=d, and k=4k=4 in dimensions 55 and 66; the conjecture asserts the full range of exponents and parameters.

Sources & referencesView supporting material

Primary source

Silouanos Brazitikos and Finlay McIntyre, “Vector-Valued Maclaurin Inequalities”, arXiv:2102.05900 (2021).

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