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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*{derived algebraic geometry} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{higher_geometry}{}\paragraph*{{Higher geometry}}\label{higher_geometry} [[!include higher geometry - contents]] \hypertarget{higher_algebra}{}\paragraph*{{Higher algebra}}\label{higher_algebra} [[!include higher algebra - contents]] \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak \noindent\hyperlink{terminology}{Terminology}\dotfill \pageref*{terminology} \linebreak \noindent\hyperlink{motivation}{Motivation}\dotfill \pageref*{motivation} \linebreak \noindent\hyperlink{history}{History}\dotfill \pageref*{history} \linebreak \noindent\hyperlink{terminology_derived_versus_}{Terminology ``derived'' versus ``$\infty$-''}\dotfill \pageref*{terminology_derived_versus_} \linebreak \noindent\hyperlink{definitions}{Definitions}\dotfill \pageref*{definitions} \linebreak \noindent\hyperlink{structured_toposes}{structured $(\infty,1)$-toposes}\dotfill \pageref*{structured_toposes} \linebreak \noindent\hyperlink{RelationToDerivedNoncommutativeGeometry}{Relation to derived noncommutative geometry}\dotfill \pageref*{RelationToDerivedNoncommutativeGeometry} \linebreak \noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak \noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak \hypertarget{idea}{}\subsection*{{Idea}}\label{idea} \emph{Derived algebraic geometry} is the specialization of [[higher geometry]] and [[homotopical algebraic geometry]] to the [[(infinity,1)-category]] of [[simplicial commutative rings]] (or sometimes, coconnective commutative [[dg-algebras]]). Hence it is a generalization of ordinary [[algebraic geometry]] where instead of [[commutative rings]], [[derived schemes]] are locally modelled on [[simplicial commutative rings]]. Derived algebraic geometry is the correct setting for certain problems arising in [[algebraic geometry]] that involve [[intersection theory]] and [[deformation theory]] (see below). \hypertarget{terminology}{}\subsection*{{Terminology}}\label{terminology} Sometimes the term \emph{derived algebraic geometry} is also used for the related subject of [[spectral algebraic geometry]], where [[commutative ring spectra]] are used instead of [[simplicial commutative rings]]. Sometimes it may also refer to the subject of [[derived noncommutative algebraic geometry]]. \hypertarget{motivation}{}\subsection*{{Motivation}}\label{motivation} There are several motivations for the study of derived algebraic geometry. \begin{enumerate}% \item The [[hidden smoothness principle]] of [[Maxim Kontsevich]], which conjectures that in classical [[algebraic geometry]], the non-[[smoothness]] of certain [[moduli spaces]] is a consequence of the fact that they are in fact truncations of [[derived moduli stacks]] (which are [[smooth]]). \item [[intersection theory|Intersection theory]]: a [[geometric]] interpretation of the [[Serre intersection formula]] for non-flat [[intersections]]. \item [[deformation theory|Deformation theory]]: a [[geometric]] interpretation of the [[cotangent complex]]. (In derived algebraic geometry, the [[cotangent complex]] $\mathbf{L}_X$ of $X$ \emph{is} its [[cotangent space]]. \end{enumerate} For more detail on the final two points, see \hyperlink{VezzosiWhatIs}{(Vezzosi, 2011)}. \hypertarget{history}{}\subsection*{{History}}\label{history} The original approach to derived algebraic geometry was via [[dg-schemes]], introduced by [[Maxim Kontsevich]]. Using [[dg-schemes]], [[Ionut Ciocan-Fontanine]] and [[Mikhail Kapranov]] constructed the first [[derived moduli spaces]] (derived [[Hilbert scheme]] and derived [[Quot scheme]]). [[Bertrand Toen]] and [[Gabriele Vezzosi]] developed [[homotopical algebraic geometry]], which is [[algebraic geometry]] in any [[HAG context]], i.e. over any [[symmetric monoidal model category]] satisfying certain assumptions. As special cases they recover the [[algebraic geometry]] of [[Grothendieck]] and the [[higher stacks]] of [[Carlos Simpson]], and also develop new theories of [[derived algebraic geometry]], [[complicial algebraic geometry]], and [[brave new algebraic geometry]]. In his thesis [[Jacob Lurie]] also developed fundamentals of derived algebraic geometry, using the language of [[structured (infinity,1)-toposes]] where [[Bertrand Toen|Toen]]-[[Gabriele Vezzosi|Vezzosi]] used [[model toposes]]. He also developed a version of derived algebraic geometry which is locally modelled on [[E-∞ rings]], called [[spectral algebraic geometry]]. \hypertarget{terminology_derived_versus_}{}\subsection*{{Terminology ``derived'' versus ``$\infty$-''}}\label{terminology_derived_versus_} The adjective ``derived'' means pretty much the same as the ``$\infty$-'' in [[∞-category]], so this is higher algebraic geometry in the sense being locally represented by higher algebras. The word stems from the use of ``derived'' as in [[derived functor]]. This came from the study of derived moduli problem. Namely to parametrize the moduli, one first looks at some space of ``cochains'' which are candidates for structures to parametrize. then one cuts those which indeed satisfy the axioms (``equations'') for the structures. Satisfying these equations is a limit-type construction, hence left exact and one is lead to right derived functors to improve; exactness on the right; this leads to use cochain complexes. The obtained moduli is too big as there are many isomorphic structures, so one needs to quotient by the automorphisms; this is a colimit type construction hence right exact. The improved quotient is the left derived functor, what is obtained by passing to stacks. \hypertarget{definitions}{}\subsection*{{Definitions}}\label{definitions} \hypertarget{structured_toposes}{}\subsubsection*{{structured $(\infty,1)$-toposes}}\label{structured_toposes} In \hyperlink{LurieStructured}{Lurie, Structured spaces} a definition of [[derived algebraic scheme]] and [[derived Deligne-Mumford stack]] is given in the wider context of [[generalized scheme]]s realized as locally affine [[structured (∞,1)-topos]]es. See these links for more details. \begin{remark} \label{}\hypertarget{}{} This definition is based on the observation that it is a deficiency of the ordinary definition of [[scheme]] to demand that underlying a scheme is a [[topological space]] and that a better definition is obtained by demanding it to have an underlying [[locale]]. But a [[locale]] is a [[0-topos]]. This motivates then the definition of a [[generalized scheme]] as a (locally affine, [[structured (infinity,1)-topos|structured]]) [[(∞,1)-topos]]. \end{remark} \hypertarget{RelationToDerivedNoncommutativeGeometry}{}\subsection*{{Relation to derived noncommutative geometry}}\label{RelationToDerivedNoncommutativeGeometry} Under some conditions, [[derived schemes]] $X$ in the sense of ([[Structured Spaces|Lurie, Structured Spaces]]) are faithfully encoded by their [[stable (∞,1)-categories]] $QCoh(X)$ of [[quasicoherent sheaves]]. This is the content of [[Tannaka duality for geometric stacks]], ([[Quasi-Coherent Sheaves and Tannaka Duality Theorems|Lurie, Quasi-Coherent Sheaves and Tannaka Duality Theorems]]). Therefore one can turn this around and declare that a suitable [[stable (∞,1)-category]] $\mathcal{A}$ which is not of the form $QCoh(X)$ for an actual [[derived scheme]] $X$ represents a generalized, ``noncommutative'' derived scheme. This is much like a [[2-category theory]] or rather [[(∞,2)-category]] theory analog of how in [[algebraic geometry]] the opposite of the category of [[monoids]] (algebras) is regarded as a category of generalized spaces. This might be (and has been) called \emph{[[2-algebraic geometry]]}. Accordingly, one can decide to regard the [[opposite (∞,1)-category]] of suitable (e.g. [[monoidal (∞,1)-category|monoidal]]) [[stable (∞,1)-categories]] as being a category of ``noncommutative derived schemes''. This is effectively the perspective on [[noncommutative algebraic geometry]] that [[Maxim Kontsevich]] has been promoting. Often and traditionally, all this is expressed in terms of certain presentations for these [[stable (∞,1)-categories]] by [[triangulated category|triangulated]] [[derived categories]] or better, [[dg-enhancement|enhancements]] as [[dg-categories]]. In this fashion then in [[derived noncommutative algebraic geometry]], a [[space]] is by definition a [[dg-category]] that is smooth and proper in an appropriate sense. The relation between [[noncommutative algebraic geometry]] and [[derived algebraic geometry]] may then be summed up by the adjunction \begin{displaymath} Pf : \DSt(k)^{op} \rightleftarrows NCSp(k) : \mathcal{M}_- \end{displaymath} where $Pf(X)$ denotes the [[dg-category]] of [[perfect complexes]] on the [[derived stack]] $X$, and $\mathcal{M}_\mathcal{C}$ denotes the [[derived moduli stack of objects in a dg-category|derived moduli stack of objects]] in the [[dg-category]] $\mathcal{C}$. See [[derived moduli stack of objects in a dg-category]] for details. \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item [[homotopical algebraic geometry]] \item [[E-∞ geometry]] \item [[dg-geometry]] \item [[spectral algebraic geometry]] \item [[brave new algebraic geometry]] \item [[higher stacks]] \item [[higher differential geometry]] \item [[derived category of coherent sheaves]] \item [[derived noncommutative algebraic geometry]] \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} (For references on [[dg-schemes]], the historical precursor to [[derived schemes]], see there.) The main references are \begin{itemize}% \item [[Jacob Lurie]], [[Derived Algebraic Geometry]] \item [[Jacob Lurie]], \emph{[[structured (∞,1)-topos|Structured Spaces]]} \end{itemize} \begin{itemize}% \item [[Bertrand Toën]], [[Gabriele Vezzosi]], \emph{Homotopical algebraic geometry II: geometric stacks and applications}, 2004, \href{http://arxiv.org/abs/math/0404373}{arXiv:math/0404373}. \item [[Bertrand Toën]], [[Gabriele Vezzosi]], \emph{From HAG to DAG: derived moduli stacks}, in Axiomatic, enriched and motivic homotopy theory, 173--216, NATO Sci. Ser. II Math. Phys. Chem., 131, Kluwer Acad. Publ., Dordrecht, 2004, \href{http://arxiv.org/abs/math/0210407}{math.AG/0210407}. \end{itemize} The following notes deal with the theory modelled on coconnective [[commutative dg-algebras]]. \begin{itemize}% \item [[Dennis Gaitsgory]], \emph{Notes on geometric Langlands: stacks}, \href{http://www.math.harvard.edu/~gaitsgde/GL/Stackstext.pdf}{pdf}. \end{itemize} The following notes deal with the theory modelled on [[E-infinity ring spectra]] ([[E-infinity geometry]]): \begin{itemize}% \item [[Clark Barwick]], \emph{Applications of derived algebraic geometry to homotopy theory}, lecture notes, mini-course in Salamanca, 2009, \href{https://dl.dropboxusercontent.com/u/1741495/papers/salamanca.pdf}{pdf}. \end{itemize} See also the surveys \begin{itemize}% \item [[Bertrand Toën]], \emph{Higher and derived stacks: a global overview}, lecture notes, 2006, \href{http://arxiv.org/abs/math/0604504}{arXiv:math/0604504}. \item [[Gabriele Vezzosi]], \emph{What is a derived stack?}, 2011, \href{http://www.ams.org/notices/201107/rtx110700955p.pdf}{pdf}. \end{itemize} \begin{itemize}% \item [[Bertrand Toën]], \emph{Derived algebraic geometry}, \href{http://arxiv.org/abs/1401.1044}{arxiv/1401.1044} \end{itemize} Discussion of [[derived noncommutative algebra]] over [[E-n algebras]] is in \begin{itemize}% \item [[John Francis]], \emph{Derived algebraic geometry over $\mathcal{E}_n$-Rings} (\href{http://math.northwestern.edu/~jnkf/writ/thezrev.pdf}{pdf}) \item [[John Francis]], \emph{The tangent complex and Hochschild cohomology of $\mathcal{E}_n$-rings} (\href{http://math.northwestern.edu/~jnkf/writ/cotangentcomplex.pdf}{pdf}) \end{itemize} \end{document}