{"title":"On definable groups and D-groups in certain fields with a generic derivation","authors":"Ya’acov Peterzil, Anand Pillay, Françoise Point","doi":"10.4153/s0008414x24000063","DOIUrl":null,"url":null,"abstract":"<p>We continue our study from Peterzil et al. (2022, <span>Preprint</span>, arXiv:2208.08293) of finite-dimensional definable groups in models of the theory <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline1.png\"><span data-mathjax-type=\"texmath\"><span>$T_{\\partial }$</span></span></img></span></span>, the model companion of an o-minimal <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline2.png\"><span data-mathjax-type=\"texmath\"><span>${\\mathcal {L}}$</span></span></img></span></span>-theory <span>T</span> expanded by a generic derivation <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline3.png\"><span data-mathjax-type=\"texmath\"><span>$\\partial $</span></span></img></span></span> as in Fornasiero and Kaplan (2021, <span>Journal of Mathematical Logic</span> 21, 2150007).</p><p>We generalize Buium’s notion of an algebraic <span>D</span>-group to <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline4.png\"><span data-mathjax-type=\"texmath\"><span>${\\mathcal {L}}$</span></span></img></span></span>-definable <span>D</span>-groups, namely <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline5.png\"><span data-mathjax-type=\"texmath\"><span>$(G,s)$</span></span></img></span></span>, where <span>G</span> is an <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline6.png\"><span data-mathjax-type=\"texmath\"><span>${\\mathcal {L}}$</span></span></img></span></span>-definable group in a model of <span>T</span>, and <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline7.png\"><span data-mathjax-type=\"texmath\"><span>$s:G\\to \\tau (G)$</span></span></img></span></span> is an <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline8.png\"><span data-mathjax-type=\"texmath\"><span>${\\mathcal {L}}$</span></span></img></span></span>-definable group section. Our main theorem says that every definable group of finite dimension in a model of <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline9.png\"><span data-mathjax-type=\"texmath\"><span>$T_\\partial $</span></span></img></span></span> is definably isomorphic to a group of the form <span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_eqnu1.png\"><span data-mathjax-type=\"texmath\"><span>$$ \\begin{align*}(G,s)^\\partial=\\{g\\in G:s(g)=\\nabla g\\},\\end{align*} $$</span></span></img></span></p><p>for some <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline10.png\"><span data-mathjax-type=\"texmath\"><span>${\\mathcal {L}}$</span></span></img></span></span>-definable <span>D</span>-group <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline11.png\"><span data-mathjax-type=\"texmath\"><span>$(G,s)$</span></span></img></span></span> (where <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline12.png\"><span data-mathjax-type=\"texmath\"><span>$\\nabla (g)=(g,\\partial g)$</span></span></img></span></span>).</p><p>We obtain analogous results when <span>T</span> is either the theory of <span>p</span>-adically closed fields or the theory of pseudo-finite fields of characteristic <span><span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240202124840300-0805:S0008414X24000063:S0008414X24000063_inline13.png\"><span data-mathjax-type=\"texmath\"><span>$0$</span></span></img></span></span>.</p>","PeriodicalId":501820,"journal":{"name":"Canadian Journal of Mathematics","volume":"15 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Canadian Journal of Mathematics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.4153/s0008414x24000063","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
We continue our study from Peterzil et al. (2022, Preprint, arXiv:2208.08293) of finite-dimensional definable groups in models of the theory $T_{\partial }$, the model companion of an o-minimal ${\mathcal {L}}$-theory T expanded by a generic derivation $\partial $ as in Fornasiero and Kaplan (2021, Journal of Mathematical Logic 21, 2150007).
We generalize Buium’s notion of an algebraic D-group to ${\mathcal {L}}$-definable D-groups, namely $(G,s)$, where G is an ${\mathcal {L}}$-definable group in a model of T, and $s:G\to \tau (G)$ is an ${\mathcal {L}}$-definable group section. Our main theorem says that every definable group of finite dimension in a model of $T_\partial $ is definably isomorphic to a group of the form $$ \begin{align*}(G,s)^\partial=\{g\in G:s(g)=\nabla g\},\end{align*} $$
for some ${\mathcal {L}}$-definable D-group $(G,s)$ (where $\nabla (g)=(g,\partial g)$).
We obtain analogous results when T is either the theory of p-adically closed fields or the theory of pseudo-finite fields of characteristic $0$.