English

On Daugavet indices of thickness

Functional Analysis 2020-05-18 v2

Abstract

Inspired by R. Whitley's thickness index the last named author recently introduced the Daugavet index of thickness of Banach spaces. We continue the investigation of the behavior of this index and also consider two new versions of the Daugavet index of thickness, which helps us solve an open problem which connect the Daugavet indices with the Daugavet equation. Moreover, we will improve the formerly known estimates of the behavior of Daugavet index on direct sums of Banach spaces by establishing sharp bounds. As a consequence of our results we prove that, for every 0<δ<20<\delta<2, there exists a Banach space where the infimum of the diameter of convex combinations of slices of the unit ball is exactly δ\delta, solving an open question from the literature. Finally, we prove that an open question posed by Ivakhno in 2006 about the relation between the radius and diameter of slices has a negative answer.

Keywords

Cite

@article{arxiv.2005.02045,
  title  = {On Daugavet indices of thickness},
  author = {Rainis Haller and Johann Langemets and Vegard Lima and Rihhard Nadel and Abraham Rueda Zoca},
  journal= {arXiv preprint arXiv:2005.02045},
  year   = {2020}
}

Comments

20 pages, compared to v1 we have now solved an open question by Y. Ivakhno and our previous Question 3.7

R2 v1 2026-06-23T15:19:01.408Z