Spahn the higher derived cahiers topos (Rev #9)

Redirected from "coherence theorem for symmetric monoidal categories".
Note: coherence and strictification for symmetric monoidal categories and coherence and strictification for symmetric monoidal categories both redirect for "coherence theorem for symmetric monoidal categories".

Confession

The Cahiers topos being the sheaf topos on the site SDCartSp of infinitessimally thickened cartesian spaces is an important example of a differentially cohesive toppos. More generally the higher cahiers topos being the (,1)(\infty,1)-sheaf (,1)(\infty,1)-topos on the (,1)(\infty,1)-site SDCartSp is an important example of a differentially cohesive (,1)(\infty,1)-topos.

However the (,1)(\infty,1)-topos arising in this way is (still) a 1-localic (i.e. localic) (,1)(\infty,1)-topos; in other words this notion of higher cahiers topos is no more intelligible than just the classical Cahiers topos. In fact there hasn’t been described any example of a differentially cohesive non-localic (,1)(\infty,1)-topos.

Apology and Redemption

What is SDCartSpS D Cart Sp? The construction is a follows: Let T:=CartSp smoothT:=Cart Sp_{smooth} denote the opposite of the category of cartesian spaces of finite dimension (as \mathbb{R}-vector spaces, so these are essentially of the form n\mathbb{R}^n). TT is the syntactic category of the Lawvere theory of smooth algebras. Define InfPointTAlg opInf Point\hookrightarrow T Alg^{op} to be the subcategory of Weil algebras; i.e. the subcategory on those objects having as vector space at least dimension 11 and which are nilpotent as algebras. Then SDCartSpS D Cart Sp is defined to be the category of objects being of the form a product n×D\mathbb{R}^n\times D with DInfPointD\in Inf Point and nn\in \mathbb{N}.

By substituting into this receipt InfPoint:=CAlg k sm op\infty Inf Point:={{C Alg_k}_{sm}}^{op} (see below) for InfPointInf Point we obtain the notion of higher derived Cahiers topos which is not nn-localic for any n<n\lt\infty. In the following shall be argued that it is differentially cohesive.

Requisites

Let SpSp denote the ∞-category of spectra, E Ring:=CAlg(Sp)E_\infty Ring:=CAlg(Sp) the ∞-category of commutative algebra objects in SpSp, for RE RingR\in E_\infty Ring let Mod R(Sp)Mod_R(Sp) denote the category of RR-module objects in SpSp. A derived moduli problem is defined to be a functor X:E RingGrpdX:E_\infty Ring\to \infty Grpd (There is also a notion of classical moduli problem where an instance is called to be enhanced by an associated derived moduli problem). For a field kk let CAlg k:=k/E RingCAlg_k:=k/E_\infty Ring denote the coslice of E RingE_\infty Ring over kk and call it the ∞-category of E E_\infty-algebras; such a kk-algebra AA is called to be discrete if its homotopy groups vanish for i0i\neq 0.

An object of the symmetric monoidal (by the usual tensor product) category Chain kChain_k of chain complexes over kk is called a commutative differential graded algebra over kk. There are functors Chain kMod kChain_k\to Mod_k and CAlg(Chain k)CAlg(Mod k)CAlg kCAlg(Chain_k)\to CAlg(Mod_k)\simeq CAlg_k. A quasi-isomorphism in CAlg dgCAlg_{dg} is defined to be a morphism inducing an isomorphism between the underlying chain complexes. There is a notion of smallness for kk-module spectra and E E_\infty-algebras over kk (see below); the corresponding full sub ∞-categories are denoted by Mod k sm{Mod_k}_sm resp. CAlg k sm{CAlg_k}_sm. A formal moduli problem over kk is defined to be a functor X:CAlg k smGrpdX:{CAlg_k}_{sm}\to \infty Grpd such that X(k)X(k) is contractible and XX preserves pullbacks of maps inducing epimorphisms between the 00-th homotopy groups.

The (Grothendieck) tangent space of a formal moduli problem X:CAlg k smGrpdX:{CAlg_k}_{sm}\to \infty Grpd is defined to be a map T X(0):=X(k[ϵ]/ϵ 2)X(k)T_X(0):=X(k[\epsilon]/\epsilon^2)\to X(k). T X(0)GrpdT_X(0)\in \infty Grpd is a topological space. Define T X(n):=X(kk[n])T_X(n):=X(k\otimes k[n]) where k[n]k[n] denotes the nn-fold shift of kk (as a kk-module spectrum). One can elaborate that T X(n1)T_X(n-1) is the loop space of T X(n)T_X(n); define the tangent complex of the formal moduli problem XX to be the sequence T X:=(T X(n)) n0T_X:=(T_X(n))_{n\ge 0}; T XT_X is a kk-module spectrum. The operation T ()T_{(-)} reflects equivalences.

Let kk be a field of characteristic zero. A differential graded Lie algebra over kk is defined to be a Lie algebra object in Chain kChain_k: a chain complex gg equipped with a binary operation [;]:ggg[-;-]:g\otimes g\to g such that [x,y]+(1) d(x)d(y)[y,x]=0[x,y]+(-1)^{d(x)d(y)}[y,x]=0 and (1) d(z)d(x)[x,[y,z]]+(1) d(x)d(y)[y,[z,x]]+(1) d(y)d(x)[z,[x,y]]=0(-1)^{d(z)d(x)}[x,[y,z]]+(-1)^{d(x)d(y)}[y,[z,x]] + (-1)^{d(y)d(x)}[z,[x,y]]=0 for homogenous elements xg d(x),yg d(y),zg d(z)x\in g_{d(x)},y\in g_{d(y)},z\in g_{d(z)}. The category of differential graded Lie algebras over kk localized at quasi-isomorphisms is denoted by Lie k dgLie_k^{dg} and just also called the category of differential graded Lie algebras over kk.

(Theorem 5.3): Let kk be a field of characteristic zero, let ModuliFun(CAlg k sm,Grpd)Moduli\hookrightarrow Fun({CAlg_k}_{sm},\infty Grpd) the full subcategory spanned by formal moduli problems over kk, let Lie k dgLie_k^{dg} denotes the ∞-category of differential graded Lie algebras over kk. Then there is an equivalence ModuliLie k dgModuli\stackrel{\sim}{\to}Lie_k^{dg}.

Proof

We first summarize the proof for the 11-localic case from [Schr11] Proposition 4.5.8: A covering family in SDCartSpS D Cart Sp is define to be of the form {U i×D(f,id)U×D}\{U_i\times D\stackrel{(f,id)}{\to}U\times D\} where {U iU}\{U_i\to U\} is a covering family in CartSp smoothCart Sp_{smooth}. Hence such a covering family by definition does not depend on the thickening components DD. ?: Since all DD are contractible a morphism VUV\to U is an epimorphisms iff D×VD×UD\times V\to D\times U is an epimorphism. Thus it suffices to show that CartSp topCart Sp_{top} is an (,1)(\infty,1)-cohesive site: CartSp topCart Sp_{top} has finite products given by m× n m+n\mathbb{R}^m\times \mathbb{R}^n\simeq \mathbb{R}^{m+n}. Every object has a point *= 0 n*=\mathbb{R}^0\to \mathbb{R}^n. Let {U iU} i\{U_i\to U\}_i be a good open covering family. This implies that the Cech nerve ζ( iU iU)[CartSp op,sSet]\zeta(\coprod_i U_i\to U)\in [Cart Sp^{op}, s Set] is degree-wise a coproduct of representables. Hence the nerve theorem implies colimζ( iU i)colimU=*colim \zeta(\coprod_i U_i)\stackrel{\sim}{\to} colim U=* is an equivalence (the statement of the nerve theorem is that colimζ(U iU)SingUcolim \zeta(U_i\to U)\simeq Sing U is an equivalence, our statement is then implied by the fact that UU as a cartesian space is contractible). Finally limζ( iU i)limU=CartSp loc(*,U)lim \zeta(\coprod_i U_i)\stackrel{\sim}{\to} lim U= Cart Sp_{loc}(*,U) is an equivalence: The morphism \sim has the right lifting property wrt. all boundary inclusions and hence it is an equivalence.

Now we define the (,1)(\infty,1)-site SDCartSp\infty S D Cart Sp: Let kk be a field. Define E Ring:=CAlg(Sp)E_\infty Ring:=C Alg (Sp), CAlg k:=k/E RingC Alg_k:=k/E_\infty Ring. For an associative ring RR let Mod R:=Chain R/qiMod_R:=Chain_R/q-i; i.e. the category of chain complexes of RR-modules modulo quasi-isomorphisms. (Definition 4.4): An object VMod kV\in Mod_k is called to be small if (1) For every integer nn, the homotopy group π n(V)\pi_n(V) is a finite dimensional kk-vector space. (2) π n(V)\pi_n(V) vanishes for n<0n\lt 0 and n>>0n\gt\gt 0. An object ACAlg kA\in CAlg_k is called to be small if it is small as a kk-module spectrum and satisfies (3): The commutative ring π 0A\pi_0 A has a unique maximal ideal pp and the composite map kπ 0Aπ 0A/pk\to \pi_0 A\to \pi_0 A/p is an isomorphism. The full subcategory of Mod kMod_k spanned by the small kk-module spectra is denoted by Mod k sm{Mod_k}_{sm}. The full subcategory of CAlg kC Alg_k spanned by the small E E_\infty-algebras over kk is denoted by CAlg k sm{CAlg_k}_{sm}. And we take

InfPoint:=CAlg k sm\infty Inf Point:={CAlg_k}_{sm}

and we could write InfPointSmoothAlg:=CAlg k=k/E Ring=k/CAlg(Sp)\infty Inf Point\hookrightarrow\infty Smooth Alg:={CAlg_k}=k/E_\infty Ring=k/CAlg(Sp)

References

Revision on February 14, 2013 at 06:04:14 by Stephan Alexander Spahn?. See the history of this page for a list of all contributions to it.