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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*{super algebra} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{superalgebra_and_supergeometry}{}\paragraph*{{Super-Algebra and Super-Geometry}}\label{superalgebra_and_supergeometry} [[!include supergeometry - contents]] \begin{quote}% from \href{Ausdehnungslehre#Grassmann44}{Grassmann 1844, p. 61 and 84} \end{quote} \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{Idea}{Idea}\dotfill \pageref*{Idea} \linebreak \noindent\hyperlink{basic_idea}{Basic idea}\dotfill \pageref*{basic_idea} \linebreak \noindent\hyperlink{AbstractIdea}{Abstract idea}\dotfill \pageref*{AbstractIdea} \linebreak \noindent\hyperlink{AssociativeSuperalgebras}{Associative superalgebras}\dotfill \pageref*{AssociativeSuperalgebras} \linebreak \noindent\hyperlink{definition}{Definition}\dotfill \pageref*{definition} \linebreak \noindent\hyperlink{superalgebras}{Superalgebras}\dotfill \pageref*{superalgebras} \linebreak \noindent\hyperlink{RelatedNotions}{Related notions}\dotfill \pageref*{RelatedNotions} \linebreak \noindent\hyperlink{examples}{Examples}\dotfill \pageref*{examples} \linebreak \noindent\hyperlink{endomorphisms_algebras_matrix_algebras}{Endomorphisms algebras, matrix algebras}\dotfill \pageref*{endomorphisms_algebras_matrix_algebras} \linebreak \noindent\hyperlink{grassmann_algebra}{Grassmann algebra}\dotfill \pageref*{grassmann_algebra} \linebreak \noindent\hyperlink{clifford_algebra}{Clifford algebra}\dotfill \pageref*{clifford_algebra} \linebreak \noindent\hyperlink{Properties}{Properties}\dotfill \pageref*{Properties} \linebreak \noindent\hyperlink{RelationToOrdinaryCommutativeAlgebra}{Relation to ordinary commutative algebras}\dotfill \pageref*{RelationToOrdinaryCommutativeAlgebra} \linebreak \noindent\hyperlink{relation_to_matrix_algebras}{Relation to matrix algebras}\dotfill \pageref*{relation_to_matrix_algebras} \linebreak \noindent\hyperlink{Picard2Groupoid}{Picard 3-group, Brauer group}\dotfill \pageref*{Picard2Groupoid} \linebreak \noindent\hyperlink{AlgebraOverSuperpoints}{Algebra in the topos over superpoints}\dotfill \pageref*{AlgebraOverSuperpoints} \linebreak \noindent\hyperlink{the_topos}{The topos}\dotfill \pageref*{the_topos} \linebreak \noindent\hyperlink{AlgebraInToposOverSuperPoints-TheLineObject}{The line object $\mathbb{R}$}\dotfill \pageref*{AlgebraInToposOverSuperPoints-TheLineObject} \linebreak \noindent\hyperlink{SuperModulesAsbbKModules}{$\mathbb{R}$-Modules}\dotfill \pageref*{SuperModulesAsbbKModules} \linebreak \noindent\hyperlink{associative_and_lie_superalgebras}{Associative and Lie Superalgebras}\dotfill \pageref*{associative_and_lie_superalgebras} \linebreak \noindent\hyperlink{properties_2}{Properties}\dotfill \pageref*{properties_2} \linebreak \noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak \noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak \noindent\hyperlink{definition_15}{Definition}\dotfill \pageref*{definition_15} \linebreak \noindent\hyperlink{brauer_groups_and_picard_2groupoid}{Brauer groups and Picard 2-groupoid}\dotfill \pageref*{brauer_groups_and_picard_2groupoid} \linebreak \hypertarget{Idea}{}\subsection*{{Idea}}\label{Idea} \hypertarget{basic_idea}{}\subsubsection*{{Basic idea}}\label{basic_idea} In the general sense, \emph{superalgebra} is the study of ([[higher algebra|higher]]) [[algebra]] \begin{itemize}% \item [[internalization|internal]] to the [[symmetric monoidal category]] of $\mathbb{Z}_2$-[[graded vector spaces]] ([[super vector spaces]]); \end{itemize} equivalently \begin{itemize}% \item over the [[base topos]] on [[superpoints]]. \end{itemize} More specifically, a \emph{[[supercommutative superalgebra]]} is an [[commutative algebra]] in the context of superalgebra. See at \emph{[[geometry of physics -- superalgebra]]} for more on this. In the following we first discuss \begin{itemize}% \item \emph{\hyperlink{AssociativeSuperalgebras}{Associative superalgebras}} \end{itemize} as [[monoids]] in the [[symmetric monoidal category]] of [[super vector spaces]]. Then we pass to the perspective of \begin{itemize}% \item \emph{\hyperlink{AlgebraOverSuperpoints}{Algebra in the topos over superpoints}} \end{itemize} and consider systematically [[algebra]] in the [[sheaf topos]] over the [[site]] of [[superpoints]] and show how this reproduces and generalizes the previous notions. See (\hyperlink{Sachse}{Sachse}) and the references at \emph{[[super ∞-groupoid]]} for some history of the topos-theoretic perspective on superalgebra. \hypertarget{AbstractIdea}{}\subsubsection*{{Abstract idea}}\label{AbstractIdea} We discuss the general abstract \emph{raison d' \^e{}tre} of super algebra. Readers looking for just the plain definition should probably \hyperlink{AssociativeSuperalgebras}{skip to below} on first reading. One way to understand the relevance of [[supercommutative superalgebra]] is [[Deligne's theorem on tensor categories]], which states that well-behaved [[tensor categories]] over the [[complex numbers]] are [[equivalence of categories|equivalent]] to [[categories of representations]] of [[supergroups]]. From this perspective the crucial sign rule is related to the [[symmetric monoidal category|symmetric]] [[braided monoidal category|braiding]] in [[tensor categories]]. This in turn may itself be understood from a more general perspective as follows. Superalgebra is [[universal property|universal]] in the following sense. The crucial super-grading rule (the ``Koszul sign rule'', \hyperlink{Grassmann1844}{Grassmann 1844, \S{}37, \S{}55}) \begin{displaymath} a \otimes b = (-1)^{deg(a) deg(b)} b \otimes a \end{displaymath} in the [[symmetric monoidal category]] of $\mathbb{Z}$-[[graded vector spaces]] is induced from the [[subcategory]] which is the [[abelian 2-group]] of metric graded [[lines]]. This in turn is the [[free construction|free]] [[abelian 2-group]] (groupal [[symmetric monoidal category]]) on a single generator. (This point of view is amplified in the first part of (\hyperlink{Kapranov13}{Kapranov 13}), whose second part is about [[super 2-algebra]], more details in \hyperlink{Kapranov15}{Kapranov 15}). Generally then super-grading and hence super-algebra arises from the [[truncated object|2-truncation]] (3-[[coskeleton]]) of the free [[abelian ∞-group]] on a single generator, which is the [[sphere spectrum]] $\mathbb{S}$. So the $\mathbb{Z}_2$-grading of superalgebra comes from the [[stable homotopy groups of spheres]] $\pi_n(\mathbb{S})$ in degree 1 and 2: \newline | [[free construction|free object]] on single [[generators and relations|generator]]: | [[abelian group]] | [[abelian 2-group]] | [[abelian 3-group]] | [[abelian 4-group]] | | | [[abelian 7-group]] | [[abelian ∞-group|abelian 8-group]] | [[abelian ∞-group]] | This suggests (as indicated in (\hyperlink{Kapranov13}{Kapranov 13}, \hyperlink{Kapranov15}{Kapranov 15})) that in full generality [[higher geometry|higher]] [[supergeometry]] is to be thought of as $\mathbb{S}$-[[graded object|graded]] geometry, hence [[Isbell duality|dually]] as [[higher algebra]] with [[∞-group of units]] [[augmented ∞-group|augmented]] over the [[sphere spectrum]]. But notice that this is canonically so for every [[E-∞ ring]], see at \emph{\href{infinity-group+of+units#AugmentedDefinition}{∞-group of units -- Augmented definition}}. This would mean: In [[higher geometry]]/[[higher algebra]] supergeometry/superalgebra is intrinsic, canonically given. Using this together with [[Hisham Sati|Sati]]`s \emph{[[Geometric and topological structures related to M-branes]]} and the [[image of the J-homomorphism]] [[!include image of J -- table]] we can derive the terminology in the above table as indicated now. \begin{quote}% The following uses the notions of \emph{[[motivic quantization]]} as indicated there, to be expanded. \end{quote} \begin{itemize}% \item \textbf{$d = 1$ [[sigma-model]]} The [[local coefficients]] for [[quantization|quantizing]] the ([[spinning particle|spinning]]) [[particle]] on the [[boundary]] of the [[string]] ending on a [[D-brane]] (by K-theoretic [[geometric quantization by push-forward]]/[[D-brane charge]]) are \begin{displaymath} \itexarray{ B BU(1) &\simeq& B K(\mathbb{Z},2) &\to& B gl_1(KU) &\to& KU \text{-}Mod } \end{displaymath} for $KU$ the [[complex K-theory spectrum]] [[E-∞ ring]], and hence the characteristic twists are in degree 2 of the group of units, hence of the \href{infinity-group%20of%20units#AugmentedDefinition}{graded ∞-group of units} \begin{displaymath} gl^{gr}_1(KU) \to \mathbb{S} \end{displaymath} hence are graded by the second [[homotopy group]] \begin{displaymath} \pi_2(\mathbb{S}) \simeq \mathbb{Z}_2 \end{displaymath} of the sphere spectrum. \item \textbf{$d = 2$ [[sigma-model]]} The [[local coefficients]] for [[quantization|quantizing]] the [[string]] (on the [[boundary]] of the [[M2-brane]] ending on an [[M9-brane]]) are \begin{displaymath} \itexarray{ B B^2 U(1) &\simeq& B K(\mathbb{Z},3) &\to& B gl_1(tmf) &\to& tmf \text{-}Mod } \end{displaymath} for the [[tmf]] [[E-∞ ring]], and hence the characteristic twists are in degree 3 of the group of units, hence of the graded group of units \begin{displaymath} gl^{gr}_1(tmf) \to \mathbb{S} \end{displaymath} hence are graded by the third [[homotopy group]] \begin{displaymath} \pi_3(\mathbb{S}) \simeq \mathbb{Z}_{24} \end{displaymath} of the sphere spectrum. \item \textbf{$d = 5$ [[sigma-model]]} The [[local coefficients]] for [[quantization|quantizing]] the [[Yang monopole]] (on the [[boundary]] of the [[M5-brane]] ending on an [[M9-brane]]) are \begin{displaymath} \itexarray{ B B^5 U(1) &\simeq& B K(\mathbb{Z},6) &\to& B gl_1(K(5)) &\to& K(5) \text{-}Mod } \,, \end{displaymath} and hence the characteristic twists are in degree 6 of the group of units, hence of the graded group of units \begin{displaymath} gl^{gr}_1(K(5)) \to \mathbb{S} \end{displaymath} hence are graded by the sixth [[homotopy group]] \begin{displaymath} \pi_6(\mathbb{S}) \simeq \mathbb{Z}_{2} \end{displaymath} of the sphere spectrum. \end{itemize} \hypertarget{AssociativeSuperalgebras}{}\subsection*{{Associative superalgebras}}\label{AssociativeSuperalgebras} \hypertarget{definition}{}\subsubsection*{{Definition}}\label{definition} \hypertarget{superalgebras}{}\paragraph*{{Superalgebras}}\label{superalgebras} An ordinary [[associative algebra]] (a [[vector space]] with a linear and associative and unital product operation) is a [[monoid]] in the [[monoidal category]] [[Vect]] of [[vector spaces]]. Throughout, fix a [[field]] $k$ of [[characteristic]] 0. \begin{defn} \label{SuperVectorSpaces}\hypertarget{SuperVectorSpaces}{} Write [[SVect]] for the [[symmetric monoidal category]] of [[super vector space]]s over $k$. This is the [[category]] of $\mathbb{Z}_2$-[[graded vector space]]s equipped with the unique non-trivial symmetric [[braided monoidal category|braided monoidal structure]]. Objects are vector spaces with a [[direct sum]] decomposition \begin{displaymath} V = V_{even} \oplus V_{odd} \end{displaymath} and the [[tensor product]] is given in terms of that on vector spaces by \begin{displaymath} V \otimes W = (V_{even} \otimes W_{even} \oplus V_{odd}\otimes W_{odd}) \oplus (V_{even} \otimes W_{odd} \oplus V_{odd} \otimes W_{even}) \end{displaymath} but equipped with the non-trivial braiding morphism \begin{displaymath} b_{V, W} : V \otimes W \to W \otimes V \end{displaymath} that is the usual braiding isomorphism of [[Vect]] on $V_{even} \otimes W_{even}$ and on $V_{even} \otimes W_{odd} \oplus V_{odd} \otimes W_{even}$ but is $(-1)$ times this on $V_{odd}\otimes W_{odd}$. \end{defn} \begin{defn} \label{SuperAlgebras}\hypertarget{SuperAlgebras}{} A \textbf{super (associative) algebra} over $K$ is a [[monoid]] in the [[symmetric monoidal category]] [[SVect]] of [[super vector space]]s. A \textbf{[[graded commutative algebra|(graded)-commutative (associative) algebra]]} over $K$ is a [[monoid]] in the [[symmetric monoidal category]] [[SVect]] of [[super vector space]]s. \end{defn} This means that a commutative superalgebra is a [[super vector space]] \begin{displaymath} A = A_{even} \oplus A_{odd} \end{displaymath} equipped with a morphism of super vector spaces \begin{displaymath} (-)\cdot (-) : A \otimes A \to A \end{displaymath} that is associative and commutative in the usual sense. Specifically for the commutativity this means that with $a,b \in A_{odd}$ we have \begin{displaymath} a \cdot b = - b \cdot a \,. \end{displaymath} Whereas if either of $a$ or $b$ is in $A_{even}$ we have \begin{displaymath} a \cdot b = b \cdot a \,. \end{displaymath} \hypertarget{RelatedNotions}{}\paragraph*{{Related notions}}\label{RelatedNotions} \begin{defn} \label{Center}\hypertarget{Center}{} The \textbf{[[center]]} of a superalgebra $A$ is the sub-superalgebra $Z(A) \hookrightarrow A$ spanned by all those elements $z \in A$ of homogeneous degree which graded-commute with all other homogeneois elements $a$. \end{defn} \begin{defn} \label{Opposite}\hypertarget{Opposite}{} For $A$ a superalgebra, its \textbf{opposite} $A^{op}$ is the superalgebra with the same underlying [[super vector space]] as $A$, and with multiplication defined on homogeneous elements by \begin{displaymath} a_1 \cdot_{A^{op}} a_2 \coloneqq (-1)^{{\vert a_1\vert}{\vert a_2\vert}} a_2 \cdot_{A} a_1 \,. \end{displaymath} \end{defn} \begin{defn} \label{CentralSimple}\hypertarget{CentralSimple}{} A superalgebra $A$ is called \textbf{central simple} if \begin{enumerate}% \item its [[center]], def. \ref{Center} is the ground field; \item its only 2-sided graded [[ideals]] are $0$ and $A$ itself. \end{enumerate} \end{defn} \begin{defn} \label{AlgWithBimodules}\hypertarget{AlgWithBimodules}{} Write $2sVect \simeq sAlg$ for the [[2-category]] equivalent to the one whose [[objects]] are superalgebra, [[1-morphisms]] are [[bimodules]] and [[2-morphisms]] are intertwiners. This is naturally a [[monoidal 2-category]]. \end{defn} \begin{defn} \label{2sVect}\hypertarget{2sVect}{} By the discussion at \emph{[[2-vector space]]} this is equivalently the 2-category of \textbf{super 2-vector spaces}. [[equivalence|Equivalence]] in $2sVect \simeq sAlg$ is also called \emph{[[Morita equivalence]]} of super-algebras. \end{defn} \begin{defn} \label{Azumaya}\hypertarget{Azumaya}{} A superalgebra is an [[Azumaya algebra]] if it is an invertible object in the [[monoidal 2-category]] $s2Vect \simeq sAlg$, def. \ref{AlgWithBimodules}. \end{defn} \begin{remark} \label{}\hypertarget{}{} The group of [[equivalence classes]] of Azumaya super algebras is called the super \emph{[[Brauer group]]}, see there for more details. \end{remark} \hypertarget{examples}{}\subsubsection*{{Examples}}\label{examples} \hypertarget{endomorphisms_algebras_matrix_algebras}{}\paragraph*{{Endomorphisms algebras, matrix algebras}}\label{endomorphisms_algebras_matrix_algebras} \begin{defn} \label{EndomorphismSuperalgebra}\hypertarget{EndomorphismSuperalgebra}{} For $V \in SVect$ a [[super vector space]], its [[endomorphism ring]] is canonically a super-algebra. Superalgebras isomorphic to ones of this form, are also called \textbf{matrix super algebras}. \end{defn} \begin{prop} \label{EndomorphismSuperalgebrasAreCentralSimple}\hypertarget{EndomorphismSuperalgebrasAreCentralSimple}{} A matrix superalgebra, def. \ref{EndomorphismSuperalgebra} is central simple, def. \ref{CentralSimple}. \end{prop} \hypertarget{grassmann_algebra}{}\paragraph*{{Grassmann algebra}}\label{grassmann_algebra} \begin{itemize}% \item For $V$ a [[vector space]] or [[graded vector space]] the [[Grassmann algebra]] $\wedge^\bullet V$ is a super algebra. This are the \emph{free} superalgebras. \end{itemize} \hypertarget{clifford_algebra}{}\paragraph*{{Clifford algebra}}\label{clifford_algebra} An class of examples of non-(graded)-commutative superalgebra are [[Clifford algebra]]. In fact, let $V$ be a [[vector space]] equipped with symmetric [[inner product]] $\langle -,- \rangle$. Write $\wedge^\bullet V$ be the [[Grassmann algebra]] on $V$. The inner product makes this a super [[Poisson algebra]]. The [[Clifford algebra]] $Cl(V, \langle -,- \rangle)$ is the [[deformation quantization]] of this. \begin{example} \label{ComplexCl1}\hypertarget{ComplexCl1}{} There is a superalgebra over the [[complex numbers]] of the form \begin{displaymath} A = \mathbb{C} \oplus \mathbb{C}\langle u\rangle \,, \end{displaymath} where the single odd generator satisfies $u \cdot u = 1$. \end{example} \hypertarget{Properties}{}\subsubsection*{{Properties}}\label{Properties} \hypertarget{RelationToOrdinaryCommutativeAlgebra}{}\paragraph*{{Relation to ordinary commutative algebras}}\label{RelationToOrdinaryCommutativeAlgebra} \begin{defn} \label{InclusionOfCommutativeSuperalgebras}\hypertarget{InclusionOfCommutativeSuperalgebras}{} Given some [[ground field]] $k$, write \begin{displaymath} \iota \colon CAlg_k \hookrightarrow SCAlg_k \end{displaymath} for the [[full subcategory]] of ordinary [[commutative algebras]] over $k$ into [[supercommutative superalgebras]] (as those having trivial odd part). \end{defn} \begin{prop} \label{AdjointsToInclusionOfPlainAlgebra}\hypertarget{AdjointsToInclusionOfPlainAlgebra}{} The inclusion $\iota$ of def. \ref{InclusionOfCommutativeSuperalgebras} has \begin{enumerate}% \item a [[right adjoint]] $(-)_{even}$ given by restricting a superalgebra to its even part; \item a [[left adjoint]] $(-)/((-)_{odd})$ given by forming the ``[[body]]'', the [[quotient]] by the ideal generated by the odd part (by the ``[[soul]]''). \end{enumerate} \end{prop} This is immediate, but conceptually important, it is made explicit for instance in (\hyperlink{CarchediRoytenberg12}{Carchedi-Roytenberg 12, example 3.18}). \begin{remark} \label{AdjointTripleBetweenPlainAndSuperalgebra}\hypertarget{AdjointTripleBetweenPlainAndSuperalgebra}{} Prop. \ref{AdjointsToInclusionOfPlainAlgebra} gives an [[adjoint triple]] of the form \begin{displaymath} CAlg_k \stackrel{\overset{(-)/((-)_{odd})}{\longleftarrow}}{\stackrel{\hookrightarrow}{\underset{(-)_{even}}{\longleftarrow}}} SCAlg_k \end{displaymath} and hence an [[adjoint cylinder]], which induces a pair of [[adjoint modalities]] ([[fermionic modality]] $\dashv$ [[bosonic modality]]). See at \emph{[[super smooth infinity-groupoid]]} for more on this. \end{remark} \hypertarget{relation_to_matrix_algebras}{}\paragraph*{{Relation to matrix algebras}}\label{relation_to_matrix_algebras} \begin{prop} \label{}\hypertarget{}{} A superalgebra is isomorphic to a matrix algebra, def. \ref{EndomorphismSuperalgebra}, precisely if it is [[equivalence|equivalent]] in $2 sVect \simeq Alg$, def. \ref{AlgWithBimodules}, ([[Morita equivalence|Morita equivalent]]) to the ground field super algebra. \end{prop} \hypertarget{Picard2Groupoid}{}\paragraph*{{Picard 3-group, Brauer group}}\label{Picard2Groupoid} We discuss the [[Picard 3-group]] of $2sVect \simeq sAlg$, def. \ref{AlgWithBimodules}, hence the corresponding [[Brauer group]]. See also at \emph{[[super line 2-bundle]]}. \begin{theorem} \label{AzumayaAreCentralSimple}\hypertarget{AzumayaAreCentralSimple}{} A superalgebra is invertible/Azumaya, def. \ref{Azumaya}, precisely if it is finite dimensional and central simple, def. \ref{CentralSimple}. \end{theorem} This is due to (\hyperlink{Wall}{Wall}). \begin{theorem} \label{}\hypertarget{}{} The [[Brauer group]] of superalgebras over the [[complex numbers]] is the [[cyclic group of order 2]]. That over the [[real numbers]] is cyclic of order 8: \begin{displaymath} sBr(\mathbb{C}) \simeq \mathbb{Z}_2 \end{displaymath} \begin{displaymath} sBr(\mathbb{R}) \simeq \mathbb{Z}_8 \,. \end{displaymath} The non-trivial element in $sBr(\mathbb{R})$ is that presented by the superalgebra $\mathbb{C} \oplus \mathbb{C} u$ of example \ref{ComplexCl1}, with $u \cdot u = 1$. \end{theorem} This is due to (\hyperlink{Wall}{Wall}). The following generalizes this to the higher [[homotopy groups]]. \begin{prop} \label{}\hypertarget{}{} The [[homotopy groups]] of the [[braided 3-group]] $sAlg^\times$ of Azumaya superalgebra are \begin{tabular}{l|l|l} &$sAlg^\times_{\mathbb{C}}$&$sAlg^\times_{\mathbb{R}}$\\ \hline $\pi_2$&$\mathbb{C}^\times$&$\mathbb{R}^\times$\\ $\pi_1$&$\mathbb{Z}_2$&$\mathbb{Z}_2$\\ $\pi_0$&$\mathbb{Z}_2$&$\mathbb{Z}_8$\\ \end{tabular} where the [[groups of units]] $\mathbb{C}^\times$ and $\mathbb{R}^\times$ are regarded as [[discrete groups]]. \end{prop} This appears in (\hyperlink{Freed}{Freed, (1.38)}). \hypertarget{AlgebraOverSuperpoints}{}\subsection*{{Algebra in the topos over superpoints}}\label{AlgebraOverSuperpoints} We now consider [[higher algebra]] in the [[(∞,1)-topos]] over [[super points]]: the [[cohesive (∞,1)-topos]] $\mathbf{H} =$ [[Super∞Grpd]]. \hypertarget{the_topos}{}\subsubsection*{{The topos}}\label{the_topos} \begin{defn} \label{}\hypertarget{}{} Write $SuperPoint$ for the [[site]] of [[superpoint]]s. Write \begin{displaymath} SuperSet := Sh(SuperPoint) \end{displaymath} for the [[sheaf topos]] (a [[presheaf topos]]) over this site. Write \begin{displaymath} Super \infty Grpd := Sh_{(\infty,1)}(SuperPoint) \end{displaymath} for the [[(∞,1)-sheaf (∞,1)-topos]] over this site: the [[(∞,1)-topos]] of [[super ∞-groupoid]]s. \end{defn} \hypertarget{AlgebraInToposOverSuperPoints-TheLineObject}{}\subsubsection*{{The line object $\mathbb{R}$}}\label{AlgebraInToposOverSuperPoints-TheLineObject} \begin{defn} \label{EmbeddingOfSupermanifoldsIntoSheavesOnSuperpoints}\hypertarget{EmbeddingOfSupermanifoldsIntoSheavesOnSuperpoints}{} Write \begin{displaymath} j \colon SuperSmthMfd \hookrightarrow Sh(SuperPoint) \end{displaymath} for the restricted [[Yoneda embedding]] of [[supermanifolds]] given by the canonical inclusion $SuperPoint \hookrightarrow SuperSmoothManifold$. \end{defn} \begin{defn} \label{TheRealLine}\hypertarget{TheRealLine}{} Write \begin{displaymath} \mathbb{R} := j(\mathbb{R}) \in Sh(SuperPoint) \end{displaymath} for the presheaf represented by the [[real line]], regarded as a [[supermanifold]]. Equipped with its canonical [[internalization|internal]] [[ring]] structure this is \begin{displaymath} \mathbb{R} \in Ring(Sh(SuperPoint)) \,. \end{displaymath} \end{defn} \begin{remark} \label{}\hypertarget{}{} By the discussion at [[supermanifold]] (in the section \href{http://ncatlab.org/nlab/show/supermanifold#AsLocallyRingedSpacesProperties}{As locally ringed spaces - Properties}) $\mathbb{R}$ sends the formal dual of a [[Grassmann algebra]] to its even subalgebra \begin{displaymath} \mathbb{R} : Spec \wedge^\bullet V \mapsto (\wedge^\bullet V)_{even} \,. \end{displaymath} This is canonically equipped with the structure of a (unital) [[commutative ring]] in $SuperSet$. \end{remark} In (\hyperlink{Sachse}{Sachse}) this appears around (21). \hypertarget{SuperModulesAsbbKModules}{}\subsubsection*{{$\mathbb{R}$-Modules}}\label{SuperModulesAsbbKModules} \begin{defn} \label{}\hypertarget{}{} Write $Mod_{\mathbb{R}}(SuperSet)$ for the [[Mod|category of modules]] over $\mathbb{R}$ of def. \ref{TheRealLine} in $SuperSet$. \end{defn} \begin{prop} \label{EmbeddingOfSVectIntoKMod}\hypertarget{EmbeddingOfSVectIntoKMod}{} The restriction of the embedding of def. \ref{EmbeddingOfSupermanifoldsIntoSheavesOnSuperpoints} to supermanifolds which are [[super vector spaces]] is a [[functor]] \begin{displaymath} j : SVect_{\mathbb{R}} = Mod_{\mathbb{R}}(Set) \hookrightarrow Mod_{\mathbb{K}}(SuperSet) \end{displaymath} from real [[super vector spaces]] to internal modules over $\mathbb{R}$ that sends $V \in SVect_{\mathbb{R}}$ to \begin{displaymath} j(V) : Spec \Lambda \mapsto (\Lambda \otimes_\mathbb{R} V)_{even} = (\Lambda_{even} \otimes_\mathbb{R} V_{even}) \oplus (\Lambda_{odd} \otimes_\mathbb{R} V_{odd}) \,. \end{displaymath} This is a [[full and faithful functor]]. \end{prop} This appears as (\hyperlink{Sachse}{Sachse, corollary 3.2}). \begin{proof} The proof is a variation on the [[Yoneda lemma]]. \end{proof} This means that ordinary [[super vector spaces]] are embedded as a [[full subcategory]] in $\mathbb{K}$-modules in the topos over [[super points]]. \hypertarget{associative_and_lie_superalgebras}{}\subsubsection*{{Associative and Lie Superalgebras}}\label{associative_and_lie_superalgebras} \begin{prop} \label{}\hypertarget{}{} The functor $j$ from prop \ref{EmbeddingOfSVectIntoKMod} induces a [[full and faithful functor]] \begin{displaymath} SAlg_{\mathbb{R}}(Set) \hookrightarrow Alg_{\mathbb{R}}(SuperSet) \end{displaymath} of superalgebras over $\mathbb{R}$ as in def. \ref{SuperAlgebras} and internal [[associative algebra]]s over $\mathbb{R}$ in $SuperSet$. Similarly we have a faithful embedding \begin{displaymath} SLieAlg_{\mathbb{R}}(Set) \hookrightarrow LieAlg_{\mathbb{R}}(SuperSet) \end{displaymath} of ordinary [[super Lie algebras]] over $\mathbb{R}$ into the internal [[Lie algebras]] over $\mathbb{R}$. \end{prop} This appears as (\hyperlink{Sachse}{Sachse, corollary 3.3}). \hypertarget{properties_2}{}\subsection*{{Properties}}\label{properties_2} (\ldots{}) \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item [[supercommutative algebra]], [[differential graded-commutative superalgebra]] [[model structure on differential graded-commutative superalgebras]] \item [[smooth superalgebra]] \item [[supermanifold]] \item [[super 2-algebra]] \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} \hypertarget{definition_15}{}\subsubsection*{{Definition}}\label{definition_15} The concept of [[Grassmann algebra]] and the super-sign rule is due to \begin{itemize}% \item [[Hermann Grassmann]], \emph{[[Ausdehnungslehre]]}, 1844 \end{itemize} Review of basic superalgebra includes \begin{itemize}% \item [[Yuri Manin]], chapter 3 of \emph{[[Gauge Field Theory and Complex Geometry]]}, Grundlehren der Mathematischen Wissenschaften 289, Springer 1988 \item [[Dennis Westra]], \emph{Superrings and supergroups}, 2009 (\href{http://www.mat.univie.ac.at/~michor/westra_diss.pdf}{pdf}) \end{itemize} Discussion of superalgebra as algebra in certain [[symmetric monoidal category|symmetric monoidal]] [[tensor categories]] is in \begin{itemize}% \item [[Pierre Deligne]], \emph{Cat\'e{}gorie Tensorielle} (\href{https://www.math.ias.edu/files/deligne/Tensorielles.pdf}{pdf}) \end{itemize} (see also at [[Deligne's theorem on tensor categories]]). Lecture notes include \begin{itemize}% \item [[Daniel Freed]], \emph{[[Five lectures on supersymmetry]]} \end{itemize} The observation that the study of super-structures in mathematics is usefully regarded as taking place over the [[base topos]] on the [[site]] of [[super points]] has been made around 1984 in \begin{itemize}% \item [[Albert Schwarz]], \emph{On the definition of superspace}, Teoret. Mat. Fiz. (1984) Volume 60, Number 1, Pages 37--42, (\href{http://www.mathnet.ru/links/b12306f831b8c37d32d5ba8511d60c93/tmf5111.pdf}{russian original pdf}) \item [[Alexander Voronov]], \emph{Maps of supermanifolds} , Teoret. Mat. Fiz. (1984) Volume 60, Number 1, Pages 43--48 \end{itemize} and in \begin{itemize}% \item V. Molotkov., \emph{Infinite-dimensional $\mathbb{Z}_2^k$-supermanifolds} , ICTP preprints, IC/84/183, 1984. \end{itemize} A summary/review is in the appendix of \begin{itemize}% \item Anatoly Konechny and [[Albert Schwarz]], \emph{On $(k \oplus l|q)$-dimensional supermanifolds} in \emph{Supersymmetry and Quantum Field Theory} ([[Dmitry Volkov]] memorial volume) Springer-Verlag, 1998, Lecture Notes in Physics, 509 , J. Wess and V. Akulov (editors)(\href{http://arxiv.org/abs/hep-th/9706003}{arXiv:hep-th/9706003}) \emph{Theory of $(k \oplus l|q)$-dimensional supermanifolds} Sel. math., New ser. 6 (2000) 471 - 486 \item [[Albert Schwarz]], I. Shapiro, \emph{Supergeometry and Arithmetic Geometry} (\href{http://arxiv.org/abs/hep-th/0605119}{arXiv:hep-th/0605119}) \end{itemize} For more along these lines see also the references at \emph{[[supermanifold]]} and at \emph{[[super infinity-groupoid]]}. Discussion in terms of [[smooth algebras]] ([[synthetic differential supergeometry]]) is in \begin{itemize}% \item [[David Carchedi]], [[Dmitry Roytenberg]], \emph{On theories of superalgebras of differentiable functions}, Theory and Applications of Categories, Vol. 28, 2013, No. 30, pp 1022-1098. (\href{http://arxiv.org/abs/1211.6134}{arxiv:1211.6134}, \href{http://www.tac.mta.ca/tac/volumes/28/30/28-30abs.html}{TAC}) \end{itemize} \hypertarget{brauer_groups_and_picard_2groupoid}{}\subsubsection*{{Brauer groups and Picard 2-groupoid}}\label{brauer_groups_and_picard_2groupoid} [[Brauer groups]] of superalgebras are discussed in \begin{itemize}% \item [[Daniel Freed]], Lectures on twisted K-theory and orientifolds (\href{http://www.ma.utexas.edu/users/dafr/ESI.pdf}{pdf}) \end{itemize} \begin{itemize}% \item [[C. T. C. Wall]], \emph{Graded Brauer groups}, J. Reine Angew. Math. 213 (1963/1964), 187-199. \end{itemize} \begin{itemize}% \item [[Pierre Deligne]], \emph{Notes on spinors} in \emph{[[Quantum Fields and Strings]]} \item [[Peter Donovan]], [[Max Karoubi]], \emph{Graded Brauer groups and K-theory with local coefficients}, Publications Math. IHES 38 (1970), 5-25 (\href{http://www.math.jussieu.fr/~karoubi/Donavan.K.pdf}{pdf}) \end{itemize} See also at \emph{[[super line 2-bundle]]} for more on this. Discussion of superalgebra as induced from free groupal symmetric monoidal categories ([[abelian 2-groups]]) and hence ultimately from the [[sphere spectrum]] is in \begin{itemize}% \item [[Mikhail Kapranov]], \emph{Categorification of supersymmetry and stable homotopy groups of spheres}, talk at \emph{\href{http://mathserver.neu.edu/~bwebster/ACRT/}{Algebra, Combinatorics and Representation Theory: in memory of Andrei Zelevinsky (1953-2013)}} April 2013 (\href{http://mathserver.neu.edu/~bwebster/ACRT/calendar-with-abstracts.pdf}{abstract pdf}, \href{https://youtu.be/StbRti1fV7A}{video}) \item [[Mikhail Kapranov]], \emph{Supergeometry in mathematics and physics}, in [[Gabriel Catren]], [[Mathieu Anel]], (eds.) \emph{[[New Spaces for Mathematics and Physics]]} (\href{http://arxiv.org/abs/1512.07042}{arXiv:1512.07042}) \item [[Mikhail Kapranov]], \emph{Super-geometry}, talk at \emph{\href{http://ercpqg-espace.sciencesconf.org/program}{New Spaces for Mathematics \& Physics}}, IHP Paris, Oct-Sept 2015 (\href{https://www.youtube.com/watch?v=bjsNwKYT8JE}{video recording}) \end{itemize} [[!redirects super algebras]] [[!redirects superalgebra]] [[!redirects super-algebra]] [[!redirects superalgebras]] [[!redirects even rules]] [[!redirects commutative superalgebra]] [[!redirects commutative superalgebras]] [[!redirects commutative super-algebra]] [[!redirects commutative super-algebras]] [[!redirects super-commutative superalgebra]] [[!redirects super-commutative superalgebras]] [[!redirects super-commutative super-algebra]] [[!redirects super-commutative super-algebras]] \end{document}