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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*{generalized complex geometry} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{complex_geometry}{}\paragraph*{{Complex geometry}}\label{complex_geometry} [[!include complex geometry - contents]] \hypertarget{differential_geometry}{}\paragraph*{{Differential geometry}}\label{differential_geometry} [[!include synthetic differential 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{on_a_vector_space}{On a vector space}\dotfill \pageref*{on_a_vector_space} \linebreak \noindent\hyperlink{on_a_manifold}{On a manifold}\dotfill \pageref*{on_a_manifold} \linebreak \noindent\hyperlink{in_terms_of_reduction_of_the_structure_group}{In terms of reduction of the structure group}\dotfill \pageref*{in_terms_of_reduction_of_the_structure_group} \linebreak \noindent\hyperlink{properties}{Properties}\dotfill \pageref*{properties} \linebreak \noindent\hyperlink{examples_2}{Examples}\dotfill \pageref*{examples_2} \linebreak \noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak \noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak \noindent\hyperlink{general}{General}\dotfill \pageref*{general} \linebreak \noindent\hyperlink{as_targets_for_models}{As targets for $\sigma$-models}\dotfill \pageref*{as_targets_for_models} \linebreak \noindent\hyperlink{mirror_symmetry}{Mirror symmetry}\dotfill \pageref*{mirror_symmetry} \linebreak \noindent\hyperlink{geometry_of_supergravity}{Geometry of supergravity}\dotfill \pageref*{geometry_of_supergravity} \linebreak \hypertarget{idea}{}\subsection*{{Idea}}\label{idea} \emph{Generalized complex geometry} is the study of the geometry of [[symplectic Lie n-algebroid|symplectic Lie 2-algebroid]] called [[standard Courant algebroid]]s $\mathfrak{c}(X)$ (over a [[smooth manifold]] $X$). This geometry of symplectic Lie 2-algebroids turns out to unify, among other things, [[complex geometry]] with [[symplectic geometry]]. This unification notably captures central aspects of [[T-duality]]. \hypertarget{Definition}{}\subsection*{{Definition}}\label{Definition} \hypertarget{on_a_vector_space}{}\subsubsection*{{On a vector space}}\label{on_a_vector_space} Let $V$ be a [[dimension|finite dimensional]] [[vector space]] over the [[real numbers]]. Recall that a \emph{[[complex structure]]} on $V$ is a [[linear map]] \begin{displaymath} J : V \to V \end{displaymath} such that $J \circ J = - id_V$. And a [[symplectic structure]] on $V$ is equivalently a linear [[isomorphism]] \begin{displaymath} \omega : V \to V^* \end{displaymath} such that \begin{displaymath} \omega^* = - \omega \,, \end{displaymath} where $V^*$ denotes the [[dual vector space]] and $\omega^*$ the dual linear map. The following definition may be thought of as combining these two concepts. \begin{defn} \label{}\hypertarget{}{} A \textbf{generalized complex structure} on $V$ is a [[linear map]] \begin{displaymath} \mathcal{J} : V \oplus V^* \to V \oplus V^* \end{displaymath} (an [[endomorphism]] of the [[direct sum]] of $V$ with its [[dual vector space]]) such that it is both \begin{enumerate}% \item a [[complex structure]] on $V \oplus V^*$ in that $\mathcal{J}^2 = - id$; \item a [[symplectic structure]] on $V \oplus V^*$ in that $\mathcal{J}^* = - \mathcal{J}$. \end{enumerate} \end{defn} The following shows that this is indeed a joint generalization of complex and symplectic structures. \begin{example} \label{}\hypertarget{}{} Let $J : V \to V$ be an ordinary complex structure on $V$. Then the linear endomorphism of $V \oplus V^*$ defined by [[matrix calculus]] as \begin{displaymath} \mathcal{J}_j := \left( \itexarray{ -J & 0 \\ 0 & J^* } \right) \end{displaymath} is a generalized complex structure on $V$. Similarly, let $\omega : V \to V^*$ be an ordinary symplectic structure on $V$. then the endomorphism \begin{displaymath} \mathcal{J}_\omega := \left( \itexarray{ 0 & - \omega^{-1} \\ \omega & 0 } \right) \end{displaymath} is a generalized complex structure on $V$. \end{example} \hypertarget{on_a_manifold}{}\subsubsection*{{On a manifold}}\label{on_a_manifold} A generalized complex structure on a manifold is a generalized complex structure on the fibers of the [[generalized tangent bundle]]. (\ldots{}) \hypertarget{in_terms_of_reduction_of_the_structure_group}{}\subsubsection*{{In terms of reduction of the structure group}}\label{in_terms_of_reduction_of_the_structure_group} A generalized complex structure on $V \oplus V^*$ is equivalently a [[reduction of the structure group]] along the inclusion \begin{displaymath} U(n,n) \hookrightarrow O(2n,2n) \,, \end{displaymath} where the left hand is identified as $U(n,n) = O(2n,2n) \cap GL(2n, \mathbb{C})$ (\hyperlink{Gualtieri}{Gualtieri, prop. 4.6}). The analog of this with the unitary group replaced by the orthogonal group yields \emph{[[type II geometry]]}. \hypertarget{properties}{}\subsection*{{Properties}}\label{properties} One finds (as described at [[standard Courant algebroid]]) that \begin{itemize}% \item choices of sub-[[Lie algebroid]]s of $\mathfrak{c}(X)$ encode (almost) \textbf{[[Dirac structure]]s} and -- after [[complexification]] -- \textbf{generalized [[complex structure]]s}; \item choices of [[section]]s of the canonical morphism $\mathfrak{c}(X) \to T X$ to the [[tangent Lie algebroid]]s encode \textbf{generalized Riemannian metrics}: pairs consisting of a (possibly [[pseudo-Riemannian metric|pseudo]]-)[[Riemannian metric]] and a [[differential form|2-form]]. In applications in [[string theory]], this encodes the field of [[gravity]] and the [[Kalb–Ramond field]], respectively. (There are also proposals for how the [[dilaton]] field appears in this context.) \end{itemize} In components these are structures found on the [[vector bundle]] \begin{displaymath} T X \oplus T^* X \,, \end{displaymath} the [[direct sum]] of the [[tangent bundle]] with the cotangent bundle of $X$. Generalized complex geometry thus generalizes and unifies \begin{itemize}% \item [[complex geometry]], \item [[symplectic geometry]], and \item [[Riemannian geometry]]. \end{itemize} It was in particular motivated by the observation that this provides a natural formalism for describing [[T-duality]]. \hypertarget{examples_2}{}\subsection*{{Examples}}\label{examples_2} \begin{itemize}% \item [[generalized Calabi-Yau manifold]] \end{itemize} \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item [[generalized tangent bundle]], [[generalized vielbein]] \item [[type II geometry]] \item [[exceptional generalized geometry]] \item [[Bn-geometry]] \item [[generalized contact geometry]] \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} \hypertarget{general}{}\paragraph*{{General}}\label{general} Generalized complex geometry was proposed by [[Nigel Hitchin]] as a formalism in [[differential geometry]] that would be suited to capture the phenomena that physicists encountered in the study of [[T-duality]]. It was later and is still developed by his students, notably Gualtieri and Cavalcanti. A standard reference is the PhD thesis \begin{itemize}% \item [[Marco Gualtieri]], \emph{Generalized complex geometry} (\href{http://arxiv.org/abs/math/0401221}{arXiv:math/0401221}) \end{itemize} A survey set of slides with an eye towards the description of the [[Kalb-Ramond field]] and [[bundle gerbe]]s is \begin{itemize}% \item [[Nigel Hitchin]], \emph{B-Fields, gerbes and generalized geometry} Oxford Durham Symposium 2005 (\href{http://www.maths.dur.ac.uk/events/Meetings/LMS/2005/GCFTST/Talks/hitchin1.pdf}{pdf}) \item [[Nigel Hitchin]], \emph{Lectures on generalized geometry} (\href{http://arxiv.org/abs/1008.0973}{arxiv/1008.0973}) \end{itemize} \hypertarget{as_targets_for_models}{}\paragraph*{{As targets for $\sigma$-models}}\label{as_targets_for_models} Generalized complex structures may serve as [[target spaces]] for [[sigma-models]]. Relations to the [[Poisson sigma-model]] and the [[Courant sigma-model]] are discussed in \begin{itemize}% \item [[Alberto Cattaneo]], Jian Qiub, [[Maxim Zabzine]], \emph{2D and 3D topological field theories for generalized complex geometry}, \href{http://projecteuclid.org/getRecord?id=euclid.atmp/1288619156}{euclid} \href{http://www.ams.org/mathscinet-getitem?mr=2721659}{MR2012a:81255} \href{http://www.math.uzh.ch/fileadmin/math/preprints/GC_BV.pdf}{pdf} \end{itemize} \hypertarget{mirror_symmetry}{}\paragraph*{{Mirror symmetry}}\label{mirror_symmetry} \begin{itemize}% \item Oren Ben-Bassat, \emph{Mirror symmetry and generalized complex manifolds. I. The transform on vector bundles, spinors, and branes}, J. Geom. Phys. \textbf{56} (2006), no. 4, 533--558 \href{http://arxiv.org/abs/math/0405303}{math.AG/0405303} \href{http://www.ams.org/mathscinet-getitem?mr=2199280}{MR2006k:53067} \href{http://dx.doi.org/10.1016/j.geomphys.2005.03.004}{doi} \end{itemize} \hypertarget{geometry_of_supergravity}{}\paragraph*{{Geometry of supergravity}}\label{geometry_of_supergravity} Generalized complex geometry and variants of [[exceptional generalized complex geometry]] are natural for describing [[supergravity]] background compactifications in [[string theory]] with their [[T-duality]] and [[U-duality]] symmetries ([[non-geometric vacua]]). \begin{itemize}% \item Ian Ellwood, \emph{NS-NS fluxes in Hitchin's generalized geometry} (\href{http://arxiv.org/abs/hep-th/0612100}{arXiv:hep-th/0612100}) \item Paulo Pires Pacheco, [[Daniel Waldram]], \emph{M-theory, exceptional generalised geometry and superpotentials} (\href{http://arxiv.org/abs/0804.1362}{arXiv:0804.1362}) \item [[Mariana Graña]], [[Ruben Minasian]], Michela Petrini, [[Daniel Waldram]], \emph{T-duality, generalized geometry and non-geometric backgrounds}, J. High Energy Phys. 2009, no. 4, 075, 39 pp. \href{http://xxx.lanl.gov/abs/0807.4527}{arXiv:0807.4527} \href{http://www.ams.org/mathscinet-getitem?mr=2505954}{MR2010i:81323} \href{http://dx.doi.org/10.1088/1126-6708/2009/04/075}{doi} \item David Andriot, [[Ruben Minasian]], Michela Petrini, \emph{Flux backgrounds from twists}, J. High Energy Phys. 2009, no. 12, 028 \href{http://arxiv.org/abs/0903.0633}{arXiv:0903.0633} \href{http://www.ams.org/mathscinet-getitem?mr=2593014}{MR2011c:81201} \href{http://dx.doi.org/10.1088/1126-6708/2009/12/028}{doi} \end{itemize} [[!redirects generalized complex structure]] [[!redirects generalized complex structures]] \end{document}