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\newtheorem{prop}{Proposition} \newtheorem{cor}{Corollary} \newtheorem*{utheorem}{Theorem} \newtheorem*{ulemma}{Lemma} \newtheorem*{uprop}{Proposition} \newtheorem*{ucor}{Corollary} \theoremstyle{definition} \newtheorem{defn}{Definition} \newtheorem{example}{Example} \newtheorem*{udefn}{Definition} \newtheorem*{uexample}{Example} \theoremstyle{remark} \newtheorem{remark}{Remark} \newtheorem{note}{Note} \newtheorem*{uremark}{Remark} \newtheorem*{unote}{Note} %------------------------------------------------------------------- \begin{document} %------------------------------------------------------------------- \section*{analytification} \begin{quote}% under construction \end{quote} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{analytic_geometry}{}\paragraph*{{Analytic geometry}}\label{analytic_geometry} [[!include analytic geometry -- contents]] \hypertarget{complex_geometry}{}\paragraph*{{Complex geometry}}\label{complex_geometry} [[!include complex geometry - contents]] \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak \noindent\hyperlink{definition}{Definition}\dotfill \pageref*{definition} \linebreak \noindent\hyperlink{examples}{Examples}\dotfill \pageref*{examples} \linebreak \noindent\hyperlink{properties}{Properties}\dotfill \pageref*{properties} \linebreak \noindent\hyperlink{Existence}{Existence and fully faithfulness (GAGA)}\dotfill \pageref*{Existence} \linebreak \noindent\hyperlink{GeometricRealizationInA1Homotopy}{As geometric realization in $\mathbb{A}^1$-homotopy theory}\dotfill \pageref*{GeometricRealizationInA1Homotopy} \linebreak \noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak \noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak \noindent\hyperlink{complex_analytification}{Complex analytification}\dotfill \pageref*{complex_analytification} \linebreak \noindent\hyperlink{ReferencesNonArchimedeanAnalytification}{Non-archimedean analytification}\dotfill \pageref*{ReferencesNonArchimedeanAnalytification} \linebreak \hypertarget{idea}{}\subsection*{{Idea}}\label{idea} Analytification is the process of universally turning an [[algebraic space]] into an [[analytic space]]. \hypertarget{definition}{}\subsection*{{Definition}}\label{definition} Let $X \to Spec(\mathbb{C})$ be a [[scheme]] of [[locally finite type]] over the [[complex numbers]]. Its set $X(\mathbb{C})$ of ``complex points'' is the set of [[maximal ideals]], since $\mathbb{C}$ is an [[algebraically closed field]], e.g. \hyperlink{Neeman07}{Neeman 07, prop. 4.2.4}). This set $X(\mathbb{C})$ canonically carries the [[complex analytic topology]]. As such it is a [[topological space]] written $X^{an}$. Equipped with the canonical [[structure sheaf]] $\mathcal{O}_{X^{an}}$ this is a [[complex analytic space]]. This $(X^{an}, \mathcal{O}_{X^{an}})$ is called the \emph{analytification} of $X$. This construction extends to a [[functor]] from the [[category]] of [[schemes]] over $\mathbb{C}$ to that of [[complex analytic spaces]]. See e.g. (\hyperlink{Neeman07}{Neeman 07, section 4, p.71}, \hyperlink{Danilov91}{Danilov 91, chapter 3, paragraph 1, section 1.1 (p.61)} Generalization to [[structured (infinity,1)-toposes]] is in (\hyperlink{Lurie08}{Lurie 08, remark 4.4.13}). \hypertarget{examples}{}\subsection*{{Examples}}\label{examples} The analytification of the [[projective space]] $\mathbb{P}^1$ is the [[complex projective space]] $(\mathbb{P}^1)^{an} \simeq \mathbb{C}\mathbb{P}^1$, hence the [[Riemann sphere]]. The analytification of an [[elliptic curve]] is the [[complex torus]]. see e.g. (\hyperlink{Danilov91}{Danilov 91, example in chapter 3, paragraph 1, section 1.1. (p. 61)}) \hypertarget{properties}{}\subsection*{{Properties}}\label{properties} \hypertarget{Existence}{}\subsubsection*{{Existence and fully faithfulness (GAGA)}}\label{Existence} The analytification of an [[algebraic space]] over the [[complex numbers]] which is \begin{enumerate}% \item [[locally of finite type]] \item [[locally separated]] \end{enumerate} is a [[complex analytic space]]. Moreover, under suitable conditions analytification is a [[fully faithful functor]]. This is a classical result due to (\hyperlink{Artin70}{Artin 70, theorem 7.3}). A textbook account of the proof is in (\hyperlink{Neeman07}{Neeman 07, section 10}). Discussion in more general [[analytic geometry]] is in (\hyperlink{ConradTemkin09}{Conrad-Temkin 09, section 2.2}). Generalization to [[algebraic stacks]]/[[Deligne-Mumford stacks]]/[[geometric stacks]] is in (\hyperlink{Lurie04}{Lurie 04}, \hyperlink{Hall11}{Hall 11}, \hyperlink{GeraschenkoZureickBrown12}{Geraschenko \& Zureick-Brown 12}). \hypertarget{GeometricRealizationInA1Homotopy}{}\subsubsection*{{As geometric realization in $\mathbb{A}^1$-homotopy theory}}\label{GeometricRealizationInA1Homotopy} For $k \hookrightarrow \mathbb{C}$ a field, then the functor that takes a smooth complex scheme to the the [[homotopy type]] underlying its analytification induces [[geometric realization]] \begin{displaymath} Sh_\infty(Sch^{sm}_k) \to Sh_\infty(Sch^{sm}_k)^{\mathbb{A}^1} \to \infty Grpd \end{displaymath} (\hyperlink{Isaksen01}{Isaksen 01}, \hyperlink{DuggerIsaksen05}{Dugger-Isaksen 05, theorem 5.2}) \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item [[GAGA]] \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} \hypertarget{complex_analytification}{}\subsubsection*{{Complex analytification}}\label{complex_analytification} Original articles include \begin{itemize}% \item [[Michael Artin]], \emph{Algebraization of formal moduli: II. Existence of modifications}, Annals of Math., 91 no. 1 (1970), pp. 88--135. \item [[Alexander Grothendieck]], [[SGA]] I, Expos\'e{} XII \end{itemize} A review of that is in \begin{itemize}% \item Yan Zhao, \emph{G\'e{}om\'e{}trie alg\'e{}brique et g\'e{}om\'e{}trie analytique}, 2013 (\href{http://pub.math.leidenuniv.nl/~jinj/2013/efg/gaga.pdf}{pdf}) \end{itemize} Textbook accounts include \begin{itemize}% \item [[Amnon Neeman]], \emph{Algebraic and analytic geometry}, London Math. Soc. Lec. Note Series \textbf{345}, 2007 (\href{http://www.cambridge.org/us/academic/subjects/mathematics/geometry-and-topology/algebraic-and-analytic-geometry}{publisher}) \item [[Vladimir Danilov]], chapter 3 of \emph{Cohomology of algebraic varieties}, in I. Shafarevich (ed.), \emph{Algebraic Geometry II}, volume 35 of \emph{Encyclopedia of mathematical sciences}, Springer 1991 (\href{http://books.google.de/books?id=ZhzXJHUgcRUC&lpg=PA67&ots=aVQoeMkBwc&dq=analytification&pg=PA61&redir_esc=y#v=onepage&q=analytification&f=false}{GoogleBooks})) \end{itemize} Discussion for [[real analytic spaces]] includes \begin{itemize}% \item [[Johannes Huisman]], section 2 of \emph{The exponential sequence in real algebraic geometry and Harnack's Inequality for proper reduced real schemes}, Communications in Algebra, Volume 30, Issue 10, 2002 (\href{http://pageperso.univ-brest.fr/~huisman/rech/publications/exphi.pdf}{pdf}) \end{itemize} Generalizations to [[higher geometry]] are in \begin{itemize}% \item [[Brian Conrad]], M. Temkin, \emph{Non-Archimedean analytification of algebraic spaces}, J. Algebraic Geom. 18 (2009), no. 4, 731--788 (\href{http://arxiv.org/abs/0706.3441}{arXiv:0706.3441}) \item [[Jacob Lurie]], \emph{[[Tannaka duality for geometric stacks]]}, (\href{http://arxiv.org/abs/math/0412266}{arXiv:math.AG/0412266}) \item [[Jacob Lurie]], \emph{[[Structured Spaces]]}, 2008 \item [[Jack Hall]], \emph{Generalizing the GAGA Principle} (\href{http://arxiv.org/abs/1101.5123}{arXiv:1101.5123}) \item [[Anton Geraschenko]], David Zureick-Brown, \emph{Formal GAGA for good moduli spaces} (\href{http://arxiv.org/abs/1208.2882}{arXiv:1208.2882}) \end{itemize} See also \begin{itemize}% \item [[Walter Gubler]]. \emph{Forms and currents on the analytification of an algebraic variety (after Chambert-Loir and Ducros)} (\href{http://arxiv.org/abs/1303.7364}{arXiv:1303.7364}) \end{itemize} Discussion in the context of [[hypercovers]] and [[A1-homotopy theory]] is in \begin{itemize}% \item [[Daniel Isaksen]], \emph{\'E{}tale realization of the $\mathbb{A}^1$-homotopy theory of schemes}, 2001 (\href{http://www.math.uiuc.edu/K-theory/0495/}{K-theory archive}) \item [[Daniel Dugger]] and [[Daniel Isaksen]], \emph{Hypercovers in topology}, 2005 (\href{http://www.math.uiuc.edu/K-theory/0528/hypercover.pdf}{pdf}, \href{http://www.math.uiuc.edu/K-theory/0528/}{K-Theory archive}) \end{itemize} \hypertarget{ReferencesNonArchimedeanAnalytification}{}\subsubsection*{{Non-archimedean analytification}}\label{ReferencesNonArchimedeanAnalytification} Discussion in more general [[rigid analytic geometry]] is in \begin{itemize}% \item [[Brian Conrad]], Michael Temkin, \emph{Non-archimedean analytification of algebraic spaces} (\href{http://arxiv.org/pdf/0706.3441}{arXiv:0706.3441}) \end{itemize} [[!redirects analytifications]] \end{document}