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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*{extended topological quantum field theory} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{functorial_quantum_field_theory}{}\paragraph*{{Functorial Quantum Field Theory}}\label{functorial_quantum_field_theory} [[!include functorial quantum field theory - contents]] \hypertarget{physics}{}\paragraph*{{Physics}}\label{physics} [[!include physicscontents]] \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak \noindent\hyperlink{definition}{Definition}\dotfill \pageref*{definition} \linebreak \noindent\hyperlink{the_category_of_extended_cobordisms}{The category of extended cobordisms}\dotfill \pageref*{the_category_of_extended_cobordisms} \linebreak \noindent\hyperlink{extended_tqft}{Extended TQFT}\dotfill \pageref*{extended_tqft} \linebreak \noindent\hyperlink{examples}{Examples}\dotfill \pageref*{examples} \linebreak \noindent\hyperlink{classes_of_examples_by_dimension}{Classes of examples by dimension}\dotfill \pageref*{classes_of_examples_by_dimension} \linebreak \noindent\hyperlink{generic_examples}{Generic examples}\dotfill \pageref*{generic_examples} \linebreak \noindent\hyperlink{specific_examples}{Specific examples}\dotfill \pageref*{specific_examples} \linebreak \noindent\hyperlink{properties}{Properties}\dotfill \pageref*{properties} \linebreak \noindent\hyperlink{construction_of_etqfts}{Construction of ETQFT's}\dotfill \pageref*{construction_of_etqfts} \linebreak \noindent\hyperlink{classification_of_etqfts}{Classification of ETQFT's}\dotfill \pageref*{classification_of_etqfts} \linebreak \noindent\hyperlink{relation_of_etqft_to_aqft}{Relation of ETQFT to AQFT}\dotfill \pageref*{relation_of_etqft_to_aqft} \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{Extended quantum field theory} (or \emph{multi-tiered quantum field theory}) is the fully [[local quantum field theory|local]] formulation of [[functorial quantum field theory]], formulated in [[higher category theory]] Whereas a \begin{itemize}% \item [[category theory|1-categorical]] [[TQFT]] may be regarded as a rule that allows one to compute topological invariants $Z(\Sigma)$ assigned to $d$-dimensional [[manifold]]s by cutting these manifolds into a sequence $\{\Sigma_i\}$ of $d$-dimensional composable [[cobordism]]s with $(d-1)$-dimensional boundaries $\partial \Sigma_i$, e.g. $\Sigma = \Sigma_2 \coprod_{\partial \Sigma_1 = \partial \Sigma_2} \Sigma_1$, then assigning quantities $Z(\Sigma_i)$ to each of these and then composing these quantities in some way, e.g. as $Z(\Sigma) = Z(\Sigma_2)\circ Z(\Sigma_1)$; \end{itemize} we have that \begin{itemize}% \item in extended [[TQFT]] $Z(\Sigma)$ may be computed by decomposing $\Sigma$ into $d$-dimensional pieces with piecewise smooth boundaries, whose boundary strata are of arbitrary codimension $k$. \end{itemize} For that reason extended QFT is also sometimes called \textbf{local} or \textbf{localized} QFT. In fact, the notion of locality in [[quantum field theory]] is precisely this notion of locality. And, as also discussed at [[FQFT]], this higher dimensional version of locality is naturally encoded in terms of [[higher category theory|n-functoriality]] of $Z$ regarded as a functor on a [[higher category theory|higher category]] of [[cobordism]]s. \hypertarget{definition}{}\subsection*{{Definition}}\label{definition} \hypertarget{the_category_of_extended_cobordisms}{}\subsubsection*{{The category of extended cobordisms}}\label{the_category_of_extended_cobordisms} The definition of a $j$-cobordism is recursive. A $(j+1)$-cobordism between $j$-cobordisms is a [[compact space|compact]] [[orientation|oriented]] $(j+1)$-dimensional [[smooth manifold]] with corners whose the boundary is the [[disjoint union]] of the target $j$-cobordism and the orientation reversal of the source $j$-cobordism. (The base case of the recursion is the [[empty set]], thought of as a $(-1)$-dimensional manifold.) $n Cob_d$ is an $n$-category with smooth compact oriented $(d-n)$-manifolds as objects and cobordisms of cobordisms up to $n$-cobordisms, up to diffeomorphism, as morphisms. There are various suggestions with more or less detail for a precise definition of a higher category $n Cob_n$ of fully extended $n$-dimensional cobordisms. A very general (and very natural) one consists in taking a further step in categorification: one takes $n$-cobordisms as $n$-morphisms and smooth homotopy classes of diffeomorphisms beween them as $(n+1)$-morphisms. Next one iterates this; see details at [[(∞,n)-category of cobordisms]]. See \begin{itemize}% \item [[extended cobordism]]. \end{itemize} \hypertarget{extended_tqft}{}\subsubsection*{{Extended TQFT}}\label{extended_tqft} Fix a [[base ring]] $R$, and let $C$ be the [[symmetric monoidal category|symmetric monoidal]] $n$-category of $n$-$R$-modules. An $n$-extended $C$-valued TQFT of dimension $d$ is a symmetric $n$-tensor functor $Z: n Cob_d \rightarrow C$ that maps \begin{itemize}% \item smooth compact oriented $d$-manifolds to elements of $R$ \item smooth compact oriented $(d-1)$-manifolds to $R$-modules \item cobordisms of smooth compact oriented $(d-1)$-manifolds to $R$-linear maps between $R$-modules \item smooth compact oriented $(d-2)$-manifolds to $R$-linear [[additive categories]] \item cobordisms of smooth compact oriented $(d-2)$-manifolds to functors between $R$-linear categories \item etc \ldots{} \item smooth compact oriented $(d-n)$-manifolds to $R$-linear $(n-1)$-categories \item cobordisms of smooth compact oriented $(d-n)$-manifolds to $(n-1)$-functors between $R$-linear $(n-1)$-categories \end{itemize} with compatibility conditions and gluing formulas that must be satisfied\ldots{} For instance, since the functor $Z$ is required to be monoidal, it sends monoidal units to monoidal units. Therefore, the $d$-dimensional [[vacuum]] is mapped to the unit element of $R$, the $(d-1)$-dimensional vacuum to the $R$-module $R$, the $(d-2)$-dimensional vacuum to the category of $R$-modules, etc. Here $n$ can range between $0$ and $d$. This generalizes to an arbitrary symmetric monoidal category $C$ as codomain category. \hypertarget{examples}{}\subsection*{{Examples}}\label{examples} \hypertarget{classes_of_examples_by_dimension}{}\subsubsection*{{Classes of examples by dimension}}\label{classes_of_examples_by_dimension} $n=1$ gives ordinary [[TQFT]]. The most common case is when $R = \mathbb{C}$ (the [[complex numbers]]), giving unitary ETQFT. The most common cases for $C$ are \begin{itemize}% \item $C = n Hilb(R)$, the category of $n$-[[n-Hilbert space|Hilbert spaces]] over a topological field $R$. As far as we know this is only defined up to $n=2$. \item $C = n Vect(R)$, the category of $n$-[[n-vector space|vector spaces]] over a field $R$. \item $C = n Mod(R)$, the (conjectured?) category of $n$-[[n-module|modules]] over a commutative ring $R$. \end{itemize} 3d: [[Turaev-Viro model]] \hypertarget{generic_examples}{}\subsubsection*{{Generic examples}}\label{generic_examples} By the [[cobordism hypothesis]]-theorem every [[fully dualizable object]] in a symmetric monoidal $(\infty,n)$-category with duals provides an example. \hypertarget{specific_examples}{}\subsubsection*{{Specific examples}}\label{specific_examples} \begin{itemize}% \item [[Levin-Wen model]] \item \href{Topological+Quantum+Field+Theories+from+Compact+Lie+Groups#3dCSFullyExtended}{Chern-Simons theory as a fully extended TQFT} \item \ldots{}many more\ldots{} \end{itemize} See also at \emph{[[TCFT]]}. \hypertarget{properties}{}\subsection*{{Properties}}\label{properties} \hypertarget{construction_of_etqfts}{}\subsubsection*{{Construction of ETQFT's}}\label{construction_of_etqfts} \begin{itemize}% \item By generators and relations \item By path integrals (this is Daniel Freed's approach) \item By modular tensor n-categories? \end{itemize} \hypertarget{classification_of_etqfts}{}\subsubsection*{{Classification of ETQFT's}}\label{classification_of_etqfts} Assume $Z: n Cob_d \rightarrow n Vect(R)$ is an extended TQFT. Since $Z$ maps the $(d-1)$-dimensional vacuum to $R$ as an $R$-vector space, by functoriality $Z$ is forced to map a $d$-dimensional closed manifold to an element of $R$. Iterating this argument, one is naturally led to conjecture that, under the correct categorical hypothesis, the behaviour of $Z$ is enterely determined by its behaviour on $(d-n)$-dimensional manifolds. See details at [[cobordism hypothesis]]. \hypertarget{relation_of_etqft_to_aqft}{}\subsubsection*{{Relation of ETQFT to AQFT}}\label{relation_of_etqft_to_aqft} See \begin{itemize}% \item [[topological chiral homology]]. \end{itemize} also \begin{itemize}% \item \emph{\href{http://arxiv.org/abs/0806.1079}{AQFT from n-functorial QFT}}. \end{itemize} \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item [[local quantum field theory]] \item [[extended Lagrangian]] \end{itemize} More on extended QFTs is also at \begin{itemize}% \item [[FQFT]] \end{itemize} [[!include Isbell duality - table]] \hypertarget{references}{}\subsection*{{References}}\label{references} \begin{itemize}% \item [[Dan Freed]], Remarks on Chern-Simons theory \item Daniel Freed, Quantum Groups from Path Integrals. \href{http://arxiv.org/abs/q-alg/9501025}{arXiv} \item Daniel Freed, Higher Algebraic Structures and Quantization. \href{http://arxiv.org/abs/hep-th/9212115}{arXiv} \item [[John Baez]] and [[James Dolan]], Higher-dimensional Algebra and Topological Quantum Field Theory. \href{http://arxiv.org/abs/q-alg/9503002}{arXiv} \item [[Jacob Lurie]], \emph{[[On the Classification of Topological Field Theories]]}. \href{http://arxiv.org/abs/0905.0465}{arXiv} \end{itemize} With an eye towards the full extension of [[Chern-Simons theory]]: \begin{itemize}% \item [[Dan Freed]], \emph{Remarks on Fully Extended 3-Dimensional Topological Field Theories} (2011) (\href{http://www.ma.utexas.edu/users/dafr/stringsmath_np.pdf}{pdf}) \item [[Dan Freed]], [[Mike Hopkins]], [[Jacob Lurie]], [[Constantin Teleman]], \emph{[[Topological Quantum Field Theories from Compact Lie Groups]]} , in P. R. Kotiuga (ed.) \emph{A celebration of the mathematical legacy of Raoul Bott} AMS (2010) (\href{http://arxiv.org/abs/0905.0731}{arXiv}) \item [[Dan Freed]], \emph{[[4-3-2 8-7-6]]}, talk at \emph{\href{https://people.maths.ox.ac.uk/tillmann/ASPECTS.html}{ASPECTS of Topology}} Dec 2012 \end{itemize} For TQFTs appearing in [[solid state physics]] in the context of [[topological order]]: \begin{itemize}% \item [[Daniel Freed]], [[Gregory Moore]], \emph{Twisted equivariant matter}, \href{http://arxiv.org/abs/1208.5055}{arxiv/1208.5055} (uses [[equivariant K-theory]] to classify free fermion gapped phases with symmetry) \item [[Daniel Freed]], \emph{Short-range entanglement and invertible field theories} (\href{http://arxiv.org/abs/1406.7278}{arXiv:1406.7278}) \end{itemize} [[!redirects EQFT]] [[!redirects extended TQFT]] [[!redirects extended quantum field theory]] [[!redirects extended QFT]] [[!redirects extended quantum field theories]] [[!redirects extended topological quantum field theories]] [[!redirects extended QFTs]] [[!redirects extended topological field theory]] [[!redirects extended topological field theories]] [[!redirects extended field theory]] [[!redirects extended field theories]] [[!redirects multi-tiered field theory]] [[!redirects multi-tiered field theories]] [[!redirects multi-tiered quantum field theory]] [[!redirects multi-tiered quantum field theories]] [[!redirects extended TQFTs]] [[!redirects extended TFT]] [[!redirects extended TFTs]] \end{document}