English

A Finite Skew Brace with Perfect Additive Group and Almost Simple Multiplicative Group

Group Theory 2026-07-15 v1

Abstract

We construct a finite skew brace whose additive group is perfect and whose multiplicative group is non-perfect and almost simple. This gives an affirmative answer to Problem 20.109 in the twenty-first edition of the Kourovka Notebook. The additive and multiplicative groups of our example are \PSU5(64)×A5and\Aut(\PSU5(64)), \PSU_5(64)\times A_5 \quad\text{and}\quad \Aut(\PSU_5(64)), respectively. The construction combines a skew brace with additive group A5A_5 and multiplicative group (C5C4)×C3(C_5\rtimes C_4)\times C_3, the splitting of the automorphism extension of \PSU5(64)\PSU_5(64), and a semidirect product of skew braces.

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Cite

@article{arxiv.2607.14059,
  title  = {A Finite Skew Brace with Perfect Additive Group and Almost Simple Multiplicative Group},
  author = {Massimiliano Di Matteo and Maria Ferrara},
  journal= {arXiv preprint arXiv:2607.14059},
  year   = {2026}
}

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6 pages