{"title":"具有复合奇点的六分双实体的双元几何学","authors":"ERIK PAEMURRU","doi":"10.1017/nmj.2024.17","DOIUrl":null,"url":null,"abstract":"Sextic double solids, double covers of <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0027763024000175_inline2.png\"/> <jats:tex-math> $\\mathbb P^3$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> branched along a sextic surface, are the lowest degree Gorenstein terminal Fano 3-folds, hence are expected to behave very rigidly in terms of birational geometry. Smooth sextic double solids, and those which are <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0027763024000175_inline3.png\"/> <jats:tex-math> $\\mathbb Q$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>-factorial with ordinary double points, are known to be birationally rigid. In this paper, we study sextic double solids with an isolated compound <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0027763024000175_inline4.png\"/> <jats:tex-math> $A_n$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> singularity. We prove a sharp bound <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0027763024000175_inline5.png\"/> <jats:tex-math> $n \\leq 8$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>, describe models for each <jats:italic>n</jats:italic> explicitly, and prove that sextic double solids with <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0027763024000175_inline6.png\"/> <jats:tex-math> $n> 3$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> are birationally nonrigid.","PeriodicalId":0,"journal":{"name":"","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"BIRATIONAL GEOMETRY OF SEXTIC DOUBLE SOLIDS WITH A COMPOUND SINGULARITY\",\"authors\":\"ERIK PAEMURRU\",\"doi\":\"10.1017/nmj.2024.17\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Sextic double solids, double covers of <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\\\"http://www.w3.org/1999/xlink\\\" mime-subtype=\\\"png\\\" xlink:href=\\\"S0027763024000175_inline2.png\\\"/> <jats:tex-math> $\\\\mathbb P^3$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> branched along a sextic surface, are the lowest degree Gorenstein terminal Fano 3-folds, hence are expected to behave very rigidly in terms of birational geometry. Smooth sextic double solids, and those which are <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\\\"http://www.w3.org/1999/xlink\\\" mime-subtype=\\\"png\\\" xlink:href=\\\"S0027763024000175_inline3.png\\\"/> <jats:tex-math> $\\\\mathbb Q$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>-factorial with ordinary double points, are known to be birationally rigid. In this paper, we study sextic double solids with an isolated compound <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\\\"http://www.w3.org/1999/xlink\\\" mime-subtype=\\\"png\\\" xlink:href=\\\"S0027763024000175_inline4.png\\\"/> <jats:tex-math> $A_n$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> singularity. We prove a sharp bound <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\\\"http://www.w3.org/1999/xlink\\\" mime-subtype=\\\"png\\\" xlink:href=\\\"S0027763024000175_inline5.png\\\"/> <jats:tex-math> $n \\\\leq 8$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>, describe models for each <jats:italic>n</jats:italic> explicitly, and prove that sextic double solids with <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\\\"http://www.w3.org/1999/xlink\\\" mime-subtype=\\\"png\\\" xlink:href=\\\"S0027763024000175_inline6.png\\\"/> <jats:tex-math> $n> 3$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> are birationally nonrigid.\",\"PeriodicalId\":0,\"journal\":{\"name\":\"\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.0,\"publicationDate\":\"2024-09-18\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://doi.org/10.1017/nmj.2024.17\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"","FirstCategoryId":"100","ListUrlMain":"https://doi.org/10.1017/nmj.2024.17","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
BIRATIONAL GEOMETRY OF SEXTIC DOUBLE SOLIDS WITH A COMPOUND SINGULARITY
Sextic double solids, double covers of $\mathbb P^3$ branched along a sextic surface, are the lowest degree Gorenstein terminal Fano 3-folds, hence are expected to behave very rigidly in terms of birational geometry. Smooth sextic double solids, and those which are $\mathbb Q$ -factorial with ordinary double points, are known to be birationally rigid. In this paper, we study sextic double solids with an isolated compound $A_n$ singularity. We prove a sharp bound $n \leq 8$ , describe models for each n explicitly, and prove that sextic double solids with $n> 3$ are birationally nonrigid.