Central idempotents of the bifree and left-free double Burnside ring

Abstract

We determine the blocks, i.e., the primitive central idempotents, of the bifree double Burnside ring $B^{\Delta }(G,G)$ and the left-free double Burnside ring $B^{\trl}(G,G)$, as well as the primitive central idempotents of the algebras arising from scalar extension to $\QQ$.

arXiv comment24 pages; minor changes; final version; to appear in Israel Journal of Mathematics