The norm inequality for dimensions of projective indecomposable modules

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Let GG be a finite group and let pp be a prime. Write

IBr⁡p(G)={φ1,…,φk}.\operatorname{IBr}_p(G)=\{\varphi_1,\ldots,\varphi_k\}.

Let φ‾=(φ1(1),…,φk(1))\overline{\varphi}=(\varphi_1(1),\ldots,\varphi_k(1)) be the vector of irreducible pp-Brauer character degrees, and let c=(cφ1,…,cφk)c=(c_{\varphi_1},\ldots,c_{\varphi_k}) be the vector of dimensions of the corresponding projective indecomposable modules. Equip Rk\mathbb{R}^k with its Euclidean scalar product and norm.

The norm inequality. The inequality

∥c∥≤∥φ‾∥\lVert c\rVert\leq\lVert\overline{\varphi}\rVert

holds for every finite group.

The inequality compares the Euclidean norms of the dimensions of projective indecomposable modules and irreducible pp-Brauer characters. The source presents it as a conjecture based on examples; no resolution is supplied here.

References

Primary source

Conchita Martínez-Pérez and Wolfgang Willems, “On the dimensions of PIM's”, arXiv:1202.5430 (2012).

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