nLab complex analytic ∞-groupoid


under construction


(,1)(\infty,1)-Topos Theory

(∞,1)-topos theory





Extra stuff, structure and property



structures in a cohesive (∞,1)-topos

Higher geometry

Complex geometry

Analytic geometry



A complex analytic \infty-groupoid is an ∞-groupoid equipped with geometric structure in the sense of complex analytic geometry, such that complex analytic spaces constitute a full subcategory of the 0-truncated complex analytic \infty-groupoids. Hence a complex analytic \infty-groupoid is an (∞,1)-sheaf/∞-stack on the site of complex manifolds (or some of its dense subsites). This is directly analogous to how (∞,1)-sheaves over the site of smooth manifolds may be regarded as smooth ∞-groupoids.



Write CplxMfdCplxMfd for the category of complex manifolds, regarded as a site with the standard Grothendieck topology.


DiscSteinSpCplxMfd \mathbb{C}Disc \hookrightarrow SteinSp \hookrightarrow CplxMfd

for the full subcategories of Stein spaces and of complex polydiscs, respectively, regarded as sites by equipping them with the induced coverages.


The inclusions in def. exhibit dense subsite inclusions.



AnalyticGrpdSh (CplxMfd) \mathbb{C}Analytic\infty Grpd \coloneqq Sh_\infty(CplxMfd)

for the hypercomplete (∞,1)-sheaf (∞,1)-topos over the sites of complex manifolds def. .


By the discussion at model structure on simplicial presheaves this means that AnalyticGrpd\mathbb{C}Analytic\infty Grpd is equivalently the simplicial localization of any of the hypercomplete local model structures on simplicial (pre-)sheaves, such as the Joyal model structure on simplicial sheaves.

This is considered in (Hopkins-Quick 12, section 2.1).




The global section geometric morphism

Γ:AnalyticGrpdGrpd \Gamma \;\colon\; \mathbb{C}Analytic\infty Grpd \longrightarrow \infty Grpd

exhibits a cohesive (∞,1)-topos.


We discuss the existence of the extra left adjoint Π\Pi (the shape modality). This proceeds essentially as in the discussion of the cohesion of Smooth∞Grpd (see there) only that where there one may choose good open covers here we have to choose genuine split hypercovers by polydiscs. The rest of the proof is verbatim as for Smooth∞Grpd.

To start with, since the hypercompletion depends only on the underlying sheaf topos of a site we may represent

AnalyticGrpdL lwhesPSh(Discs) proj,loc \mathbb{C}Analytic\infty Grpd \simeq L_{lwhe} sPSh(\mathbb{C}Discs)_{proj, loc}

by the simplicial localization of the local model structure on simplicial presheaves over Disc\mathbb{C}Disc, localized (by the theorem of descent recognition along hypercovers) at the hypercovers U XU_\bullet\to X as seen over CplxMfdCplxMfd restricted to XX a polydisc (this roundabout way since Disc\mathbb{C}Disc does not carry a Grothendieck topology but just a coverage).

Now before Bousfield localization we have a simplicially enriched Quillen adjunction

sPSh(Disc) proj,locΔlimsSet Quillen sPSh(\mathbb{C}Disc)_{proj, loc} \stackrel{\overset{\underset{\to}{\lim}}{\longrightarrow}}{\underset{\Delta}{\longleftarrow}} sSet_{Quillen}

which is simplicial-degree wise just the defining adjunction of the colimit functor lim\underset{\to}{\lim} left adjoint to the constant presheaf functor.

To see that this descends to a Quillen adjunction on the local model structure, by the recognition theorem for simplicial Quillen adjunctions we hence need to check that Δ\Delta preserves fibrant objects with respect to the local model structure, hence that any constant simplicial presheaf ΔS\Delta S for SS a Kan complex already satisfies descent with respect to hypercovers as seen over CplxMfdCplxMfd.

By the theorem of descent recognition along hypercovers ΔS\Delta S satisfies descent precisely if for each hypercover U XU_\bullet \to X of any polydisc XX. the induced morphism of derived hom-spaces

RHom(X,ΔS)RHom(U ,ΔS) RHom(X, \Delta S) \longrightarrow RHom(U_\bullet, \Delta S)

in the global model structure on simplicial presheaves is a weak equivalence. This RHomRHom in turn may be computed as the sSetsSet-enriched hom object out of a cofibrant resolution X^X\hat X \to X and U^ U \hat U_\bullet \to U_\bullet, respectively. By the recognition of cofibrant objects in the projective model structure the representable XX is already cofibrant and a sufficient condition for a resolution U^ U \hat U_\bullet \to U_\bullet to be cofibrant is that it is a split hypercover.

Since DiscCplxMfd\mathbb{C}Disc \hookrightarrow CplxMfd is a dense subsite, we may always choose such a split hypercover such that U^ \hat U_\bullet consists simplicial-degreewise of coproducts of polydiscs: by the proposition at hypercover – Existence of split refinements

Since the colimit of a representable functor is the point, this means that with such a choice limU^ \underset{\to}{\lim} \hat U_\bullet is the simplicial set obtained by replacing in the hypercover by polydiscs each polydisc by a point. Forgetting the complex structure on all manifolds involved, one sees that this is precisely the “etale homotopy type” of XX as seen by the site CartSp of Cartesian spaces, by the discussion at Smooth∞Grpd, and this comes out as the ordinary homotopy type of the underlying topological space of XX. But this is of course contractible.

In conclusion this means that

RHom(U ,ΔS) sPSh(Disc)(U^ ,ΔS) sSet(Sing(X),S) sSet(*,S) S \begin{aligned} RHom(U_\bullet, \Delta S) &\simeq sPSh(\mathbb{C}Disc)(\hat U_\bullet, \Delta S) \\ & \simeq sSet(Sing(X), S) \\ & \simeq sSet(\ast, S) \\ &\simeq S \end{aligned}

Therefore the descent condition for ΔS\Delta S is satisfied. (This is also the statement of (Hopkins-Quick 12, lemma 2.3, prop. 2.4, lemma 2.5, prop. 2.6)).

From here on the argument for the cohesion of AnalyticGrpd\mathbb{C}Analytic \infty Grpd proceeds as at ∞-cohesive site (which might just as well be adapted to the hyper-discussion here).


For XCplxMfdAnalyticGrpdX\in CplxMfd \hookrightarrow \mathbb{C}Analytic\infty Grpd a complex manifold, then the shape Π(X)\Pi(X) is the homotopy type of its underlying topological space.

In (Hopkins-Quick 12)) this is part of prop. 2.6.

Oka principle

Discussion of the Oka principle in terms of AnalyticGrpd\mathbb{C}Analytic\infty Grpd is in (Larusson 01).


Say that a complex manifold XX is an Oka manifold if for every Stein manifold Σ\Sigma the canonical inclusion

Maps hol(Σ,X)Maps top(Σ,X) Maps_{hol}(\Sigma, X) \longrightarrow Maps_{top}(\Sigma, X)

from the mapping space of holomorphic functions to that of continuous functions (both equipped with the compact-open topology) is a weak homotopy equivalence.


This is the case precisely if Maps hol(,X)Psh (SteinSp)Maps_{hol}(-,X) \in Psh_\infty(SteinSp) satisfies descent with respect to finite covers.

(Larusson 01, theorem 2.1)


By corollary , in terms of cohesion, prop. , definition should (…check…) read

Π[Σ,X][Π(Σ),Π(X)]. \Pi[\Sigma,X] \simeq \flat [\Pi(\Sigma), \Pi(X)] \,.

Complex analytic differential generalized cohomology

By prop. AnalyticGrpd\mathbb{C}Analytic \infty Grpd is cohesive and hence by the discussion at differential cohomology hexagon the objects E^Stab(AnalyticGrpd)\hat E \in Stab(\mathbb{C}Analytic \infty Grpd) (hence the sheaves of spectra on Mfd\mathbb{C}Mfd ) qualify as differential cohomology refinements of the cohomology theories represented by the shapes EΠE^E\coloneqq \Pi \hat E \in Spectra.

Discussion of such complex analytic differential generalized cohomology is in (Hopkins-Quick 12, section 4),.


Multiplicative group and holomorphic line nn-bundles

The multiplicative group is a canonical ∞-group object

𝔾 mGrp(AnalyticGrpd) \mathbb{G}_m \in Grp(\mathbb{C}Analytic\infty Grpd)

given as an (∞,1)-presheaf by the assignment

𝔾 m:Σ𝒪 Σ × \mathbb{G}_m \;\colon\; \Sigma \mapsto \mathcal{O}_\Sigma^\times

that sends a Stein manifold to the multiplicative abelian group of non-vanishing holomorphic functions on it.

The delooping B𝔾 m\mathbf{B}\mathbb{G}_m is the universal moduli stack for holomorphic line bundles (the Picard stack) and the double delooping B 2𝔾 m\mathbf{B}^2 \mathbb{G}_m that for holomorphic line 2-bundles (the Brauer stack).


Last revised on November 20, 2021 at 07:31:24. See the history of this page for a list of all contributions to it.