{"title":"CHARACTER STACKS ARE PORC COUNT","authors":"Nick Bridger, Masoud Kamgarpour","doi":"10.1017/s1446788722000179","DOIUrl":"https://doi.org/10.1017/s1446788722000179","url":null,"abstract":"\u0000 We compute the number of points over finite fields of the character stack associated to a compact surface group and a reductive group with connected centre. We find that the answer is a polynomial on residue classes (PORC). The key ingredients in the proof are Lusztig’s Jordan decomposition of complex characters of finite reductive groups and Deriziotis’s results on their genus numbers. As a consequence of our main theorem, we obtain an expression for the E-polynomial of the character stack.","PeriodicalId":50007,"journal":{"name":"Journal of the Australian Mathematical Society","volume":"12 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2022-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75454684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"$boldsymbol {C}^{*}$\u0000 -ALGEBRAS FROM \u0000$boldsymbol {K}$\u0000 GROUP REPRESENTATIONS","authors":"V. Deaconu","doi":"10.1017/S1446788721000392","DOIUrl":"https://doi.org/10.1017/S1446788721000392","url":null,"abstract":"Abstract We introduce certain \u0000$C^*$\u0000 -algebras and k-graphs associated to k finite-dimensional unitary representations \u0000$rho _1,ldots ,rho _k$\u0000 of a compact group G. We define a higher rank Doplicher-Roberts algebra \u0000$mathcal {O}_{rho _1,ldots ,rho _k}$\u0000 , constructed from intertwiners of tensor powers of these representations. Under certain conditions, we show that this \u0000$C^*$\u0000 -algebra is isomorphic to a corner in the \u0000$C^*$\u0000 -algebra of a row-finite rank k graph \u0000$Lambda $\u0000 with no sources. For G finite and \u0000$rho _i$\u0000 faithful of dimension at least two, this graph is irreducible, it has vertices \u0000$hat {G}$\u0000 and the edges are determined by k commuting matrices obtained from the character table of the group. We illustrate this with some examples when \u0000$mathcal {O}_{rho _1,ldots ,rho _k}$\u0000 is simple and purely infinite, and with some K-theory computations.","PeriodicalId":50007,"journal":{"name":"Journal of the Australian Mathematical Society","volume":"34 1","pages":"318 - 338"},"PeriodicalIF":0.7,"publicationDate":"2022-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90988189","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}