{"title":"有限群逼近性质的坏地方","authors":"Felipe Rivera-Mesas","doi":"10.5802/jtnb.1199","DOIUrl":null,"url":null,"abstract":"Given a number field $k$ and a finite $k$-group $G$, the Tame Approximation Problem for $G$ asks whether the restriction map $H^1(k,G)\\to\\prod_{v\\in\\Sigma}H^1(k_v,G)$ is surjective for every finite set of places $\\Sigma\\subseteq\\Omega_k$ disjoint from $\\text{Bad}_G$, where $\\text{Bad}_G$ is the finite set of places that either divides the order of $G$ or ramifies in the minimal extension splitting $G$. In this paper we prove that the set $\\text{Bad}_G$ is \"sharp\". To achieve this we prove that there are finite abelian $k$-groups $A$ where the map $H^1(k,A)\\to\\prod_{v\\in\\Sigma_0}H^1(k_v,A)$ is not surjective in a set $\\Sigma_0\\subseteq\\text{Bad}_A$ with particular properties, namely $\\Sigma_0$ is the set of places that do not divide the order of $A$ and ramify in the minimal extension splitting $A$.","PeriodicalId":48896,"journal":{"name":"Journal De Theorie Des Nombres De Bordeaux","volume":" ","pages":""},"PeriodicalIF":0.3000,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"1","resultStr":"{\"title\":\"Bad places for the approximation property for finite groups\",\"authors\":\"Felipe Rivera-Mesas\",\"doi\":\"10.5802/jtnb.1199\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Given a number field $k$ and a finite $k$-group $G$, the Tame Approximation Problem for $G$ asks whether the restriction map $H^1(k,G)\\\\to\\\\prod_{v\\\\in\\\\Sigma}H^1(k_v,G)$ is surjective for every finite set of places $\\\\Sigma\\\\subseteq\\\\Omega_k$ disjoint from $\\\\text{Bad}_G$, where $\\\\text{Bad}_G$ is the finite set of places that either divides the order of $G$ or ramifies in the minimal extension splitting $G$. In this paper we prove that the set $\\\\text{Bad}_G$ is \\\"sharp\\\". To achieve this we prove that there are finite abelian $k$-groups $A$ where the map $H^1(k,A)\\\\to\\\\prod_{v\\\\in\\\\Sigma_0}H^1(k_v,A)$ is not surjective in a set $\\\\Sigma_0\\\\subseteq\\\\text{Bad}_A$ with particular properties, namely $\\\\Sigma_0$ is the set of places that do not divide the order of $A$ and ramify in the minimal extension splitting $A$.\",\"PeriodicalId\":48896,\"journal\":{\"name\":\"Journal De Theorie Des Nombres De Bordeaux\",\"volume\":\" \",\"pages\":\"\"},\"PeriodicalIF\":0.3000,\"publicationDate\":\"2020-09-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"1\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal De Theorie Des Nombres De Bordeaux\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://doi.org/10.5802/jtnb.1199\",\"RegionNum\":4,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal De Theorie Des Nombres De Bordeaux","FirstCategoryId":"100","ListUrlMain":"https://doi.org/10.5802/jtnb.1199","RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"MATHEMATICS","Score":null,"Total":0}
Bad places for the approximation property for finite groups
Given a number field $k$ and a finite $k$-group $G$, the Tame Approximation Problem for $G$ asks whether the restriction map $H^1(k,G)\to\prod_{v\in\Sigma}H^1(k_v,G)$ is surjective for every finite set of places $\Sigma\subseteq\Omega_k$ disjoint from $\text{Bad}_G$, where $\text{Bad}_G$ is the finite set of places that either divides the order of $G$ or ramifies in the minimal extension splitting $G$. In this paper we prove that the set $\text{Bad}_G$ is "sharp". To achieve this we prove that there are finite abelian $k$-groups $A$ where the map $H^1(k,A)\to\prod_{v\in\Sigma_0}H^1(k_v,A)$ is not surjective in a set $\Sigma_0\subseteq\text{Bad}_A$ with particular properties, namely $\Sigma_0$ is the set of places that do not divide the order of $A$ and ramify in the minimal extension splitting $A$.