arXiv subjects

David Carchedi

Publications and source records attributed to David Carchedi.

14 recordsLinked to original sources

arXiv2025

Quasi-coherent sheaves and D-modules in Derived Differential Supergeometry

Derived geometry provides powerful tools to handle non-transverse intersections and singular moduli problems arising in geometry and theoretical physics. While derived algebraic geometry has been extensively developed, classical field theories -- formulated as variational problems involving sections of smooth fiber bundles over manifolds -- naturally require the language of differential geometry, infinite-dimensional analysis (e.g., Fr\'echet manifolds), and additional geometric structures on spacetime, such as smooth metrics. Moreover, field theories incorporating fermionic matter fields necessitate extending the framework to include supermanifolds. This article is the first in a sequence aimed at rigorously modeling the derived space of solutions to the field equations of Lagrangian gauge theories as derived $\Ci$-stacks. While this article does not explicitly discuss physics or field theory, it develops foundational aspects of derived differential geometry which are useful in their own right and contribute to the further development of the field. Moreover, these results provide essential groundwork for subsequent papers rigorously constructing derived spaces of solutions to Euler-Lagrange equations. We establish foundational results extending existing work on derived manifolds into supergeometric and infinite-dimensional contexts, and explicitly relate these constructions to differential operators and PDE theory. This paper an excerpt from a larger manuscript currently in preparation and is made available now to disseminate key foundational developments.

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arXiv2023

Derived Manifolds as Differential Graded Manifolds

On one hand, together with Pelle Steffens, we recently characterized the infinity category of derived manifolds up to equivalence by a universal property. On the other hand, it is shown in recent work of Behrend-Liao-Xu that the category of differential graded manifolds admits a homotopy theory. In this paper, we prove that the associated infinity category of dg-manifolds is equivalent to that of derived manifolds. This allows the well developed theory of dg-geometry to live in symbiosis with infinity categorical approach to derived differential geometry. As a consequence, we prove that a dg-C-infinity-algebra is homotopically finitely presented if and only if it is quasi-isomorphic to smooth functions on a dg-manifold.

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arXiv2019

On the Universal Property of Derived Manifolds

It is well known that any model for derived manifolds must form a higher category. In this paper, we propose a universal property for this higher category, classifying it up to equivalence. Namely, the $\infty$-category $\mathbf{DMfd}$ of derived manifolds has finite limits, is idempotent complete, and receives a functor from the category of manifolds which preserves transverse pullbacks and the terminal object, and moreover is universal with respect to these properties. We then show this universal property is equivalent to another one, intimately linking the $\infty$-category of derived manifolds to the theory of $C^\infty$-rings. More precisely, $\mathbb{R}$ is a $C^\infty$-ring object in $\mathbf{DMfd}$, and the pair $\left(\mathbf{DMfd},\mathbb{R}\right)$ is universal among idempotent complete $\infty$-categories with finite limits and a $C^\infty$-ring object. We then show that (a slight extension beyond the quasi-smooth setting of) Spivak's original model satisfies our universal property.

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arXiv2019

On the profinite homotopy type of log schemes

We complete the program, initiated in [6], to compare the many different possible definitions of the underlying homotopy type of a log scheme. We show that, up to profinite completion, they all yield the same result, and thus arrive at an unambiguous definition of the profinite homotopy type of a log scheme. Specifically, in [6], we define this to be the profinite étale homotopy type of the infinite root stack, and show that, over $\mathbb{C},$ this agrees up to profinite completion with the Kato-Nakayama space. Other possible candidates are the profinite shape of the Kummer étale site $X_{\mbox{két}},$ or of the representable étale site of $\sqrt[\infty]{X}.$ Our main result is that all of these notions agree, and moreover the profinite étale homotopy type of the infinite root stack is not sensitive to whether or not it is viewed as a pro-system in stacks, or as an actual stack (by taking the limit of the pro-system). We furthermore show that in the log regular setting, all these notions also agree with the étale homotopy type of the classical locus $X^{\mbox{triv}}$ (up to an appropriate completion). We deduce that, over an arbitrary locally Noetherian base, the étale homotopy type of $\mathbb{G}_m^N$ agrees with that of $Bμ_\infty^N$ up to completion.

math.AG↗

arXiv2018

Relative Étale Realizations of Motivic Spaces and Dwyer-Friedlander $K$-Theory of Noncommutative Schemes

In this paper, we construct a refined, relative version of the étale realization functor of motivic spaces, first studied by Isaksen and Schmidt. Their functor goes from the $\infty$-category of motivic spaces over a base scheme $S$ to the $\infty$-category of $p$-profinite spaces, where $p$ is a prime which is invertible in all residue fields of $S$. In the first part of this paper, we refine the target of this functor to an $\infty$-category where $p$-profinite spaces is a further completion. Roughly speaking, this $\infty$-category is generated under cofiltered limits by those spaces whose associated "local system" on $S$ is $A^1$-invariant. We then construct a new, relative version of their étale realization functor which takes into account the geometry and arithmetic of the base scheme $S$. For example, when $S$ is the spectrum of a field $k$, our functor lands in a certain $\infty$-category equivariant for the absolute Galois group. Our construction relies on a relative version of étale homotopy types in the sense of Artin-Mazur-Friedlander, which we also develop in some detail, expanding on previous work of Barnea-Harpaz-Schlank. We then stabilize our functor, in the $S^1$-direction, to produce an étale realization functor for motivic $S^1$-spectra (in other words, Nisnevich sheaves of spectra which are $A^1$-invariant). To this end, we also develop an $\infty$-categorical version of the theory of profinite spectra, first explored by Quick. As an application, we refine the construction of the étale $K$-theory of Dwyer and Friedlander, and define its non-commutative extension. This latter invariant should be seen as an $\ell$-adic analog of Blanc's theory of semi-topological $K$-theory of non-commutative schemes. We then formulate and prove an analog of Blanc's conjecture on the torsion part of this theory, generalizing the work of Antieau and Heller.

math.AG↗

arXiv2016

Kato-Nakayama spaces, infinite root stacks, and the profinite homotopy type of log schemes

For a log scheme locally of finite type over $\mathbb{C}$, a natural candidate for its profinite homotopy type is the profinite completion of its Kato-Nakayama space. Alternatively, one may consider the profinite homotopy type of the underlying topological stack of its infinite root stack. Finally, for a log scheme not necessarily over $\mathbb{C}$, another natural candidate is the profinite étale homotopy type of its infinite root stack. We prove that, for a fine saturated log scheme locally of finite type over $\mathbb{C}$, these three notions agree. In particular, we construct a comparison map from the Kato-Nakayama space to the underlying topological stack of the infinite root stack, and prove that it induces an equivalence on profinite completions. In light of these results, we define the profinite homotopy type of a general fine saturated log scheme as the profinite étale homotopy type of its infinite root stack.

math.AG↗

arXiv2016

On the étale homotopy type of higher stacks

A new approach to étale homotopy theory is presented which applies to a much broader class of objects than previously existing approaches, namely it applies not only to all schemes (without any local Noetherian hypothesis), but also to arbitrary higher stacks on the étale site of such schemes, and in particular to all algebraic stacks. This approach also produces a more refined invariant, namely a pro-object in the infinity category of spaces, rather than in the homotopy category. We prove a profinite comparison theorem at this level of generality, which states that if $\mathcal{X}$ is an arbitrary higher stack on the étale site of affine schemes of finite type over $\mathbb{C},$ then the étale homotopy type of $\mathcal{X}$ agrees with the homotopy type of the underlying stack $\mathcal{X}_{top}$ on the topological site, after profinite completion. In particular, if $\mathcal{X}$ is an Artin stack locally of finite type over $\mathbb{C}$, our definition of the étale homotopy type of $\mathcal{X}$ agrees up to profinite completion with the homotopy type of the underlying topological stack $\mathcal{X}_{top}$ of $\mathcal{X}$ in the sense of Noohi. In order to prove our comparison theorem, we provide a modern reformulation of the theory of local systems and their cohomology using the language of $\infty$-categories which we believe to be of independent interest.

math.AG↗

arXiv2016

Higher Orbifolds and Deligne-Mumford Stacks as Structured Infinity Topoi

We develop a universal framework to study smooth higher orbifolds on the one hand and higher Deligne-Mumford stacks (as well as their derived and spectral variants) on the other, and use this framework to obtain a completely categorical description of which stacks arise as the functor of points of such objects. We choose to model higher orbifolds and Deligne-Mumford stacks as infinity-topoi equipped with a structure sheaf, thus naturally generalizing the work of Lurie, but our approach applies not only to different settings of algebraic geometry such as classical algebraic geometry, derived algebraic geometry, and the algebraic geometry of commutative ring spectra as in Lurie's work, but also to differential topology, complex geometry, the theory of supermanifolds, derived manifolds etc., where it produces a theory of higher generalized orbifolds appropriate for these settings. This universal framework yields new insights into the general theory of Deligne-Mumford stacks and orbifolds, including a representability criterion which gives a categorical characterization of such generalized Deligne-Mumford stacks. This specializes to a new categorical description of classical Deligne-Mumford stacks, a result sketched in previous work of the author, which extends to derived and spectral Deligne-Mumford stacks as well.

math.CT↗

arXiv2015

On The Homotopy Type of Higher Orbifolds and Haefliger Classifying Spaces

We describe various equivalent ways of associating to an orbifold, or more generally a higher étale differentiable stack, a weak homotopy type. Some of these ways extend to arbitrary higher stacks on the site of smooth manifolds, and we show that for a differentiable stack X arising from a Lie groupoid G, the weak homotopy type of X agrees with that of BG. Using this machinery, we are able to find new presentations for the weak homotopy type of certain classifying spaces. In particular, we give a new presentation for the Borel construction of an almost free action of a Lie group G on a smooth manifold M as the classifying space of a category whose objects consists of smooth maps R^n to M which are transverse to all the G-orbits, where n=dim M - dim G. We also prove a generalization of Segal's theorem, which presents the weak homotopy type of Haefliger's groupoid $Γ^q$ as the classifying space of the monoid of self-embeddings of R^q, and our generalization gives analogous presentations for the weak homotopy type of the Lie groupoids $Γ^{Sp}_{2q}$ and $RΓ^q$ which are related to the classification of foliations with transverse symplectic forms and transverse metrics respectively. We also give a short and simple proof of Segal's original theorem using our machinery.

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arXiv2013

Étale Stacks as Prolongations

In this article, we derive many properties of étale stacks in various contexts, and prove that étale stacks may be characterized categorically as those stacks that arise as prolongations of stacks on a site of spaces and local homeomorphisms. Moreover, we show that the bicategory of étale differentiable stacks and local diffeomorphisms is equivalent to the 2-topos of stacks on the site of smooth manifolds and local diffeomorphisms. An analogous statement holds for other flavors of manifolds (topological, $C^k,$ complex, super...), and topological spaces locally homeomorphic to a given space $X.$ A slight modification of this result also holds in an even more general context, including all étale topological stacks, and Zariski étale stacks, and we also sketch a proof of an analogous characterization of Deligne-Mumford algebraic stacks. We go on to characterize effective étale stacks as precisely those stacks arising as the prolongations of sheaves. It follows that étale stacks (and in particular orbifolds) induce a small gerbe over their effective part, and all gerbes over effective étale stacks arise in this way. As an application, we show that well known Lie groupoids arising in foliation theory give presentations for certain moduli stacks. For example, there exists a classifying stack for Riemannian metrics, presented by Haefliger's groupoid $RΓ$ and submersions into this stack classify Riemannian foliations, and similarly for symplectic structures, with the role of $RΓ$ replaced with $Γ^{Sp}.$ We also prove some unexpected results, for example: the category of smooth $n$-manifolds and local diffeomorphisms has binary products.

math.DG↗

arXiv2013

On Theories of Superalgebras of Differentiable Functions

This is the first in a series of papers laying the foundations for a differential graded approach to derived differential geometry (and other geometries in characteristic zero). In this paper, we study theories of supercommutative algebras for which infinitely differentiable functions can be evaluated on elements. Such a theory is called a super Fermat theory. Any category of superspaces and smooth functions has an associated such theory. This includes both real and complex supermanifolds, as well as algebraic superschemes. In particular, there is a super Fermat theory of C-infinity superalgebras. C-infinity superalgebras are the appropriate notion of supercommutative algebras in the world of C-infinity rings, the latter being of central importance both to synthetic differential geometry and to all existing models of derived smooth manifolds. A super Fermat theory is a natural generalization of the concept of a Fermat theory introduced by E. Dubuc and A. Kock. We show that any Fermat theory admits a canonical superization, however not every super Fermat theory arises in this way. For a fixed super Fermat theory, we go on to study a special subcategory of algebras called near-point determined algebras, and derive many of their algebraic properties.

math.DG↗

arXiv2012

Homological Algebra for Superalgebras of Differentiable Functions

This is the second in a series of papers laying the foundations for a differential graded approach to derived differential geometry (and other geometries in characteristic zero). In this paper, we extend the classical notion of a dg-algebra to define, in particular, the notion of a differential graded algebra in the world of C-infinity rings. The opposite of the category of differential graded C-infinity algebras contains the category of differential graded manifolds as a full subcategory. More generally, this notion of differential graded algebra makes sense for algebras over any (super) Fermat theory, and hence one also arrives at the definition of a differential graded algebra appropriate for the study of derived real and complex analytic manifolds and other variants. We go on to show that, for any super Fermat theory S which admits integration, a concept we define and show is satisfied by all important examples, the category of differential graded S-algebras supports a Quillen model structure naturally extending the classical one on differential graded algebras, both in the bounded and unbounded case (as well as differential algebras with no grading). Finally, we show that, under the same assumptions, any of these categories of differential graded S-algebras have a simplicial enrichment, compatible in a suitable sense with the model structure.

math.AG↗

arXiv2012

Sheaf Theory for Étale Geometric Stacks

We generalize the notion of a small sheaf of sets over a topological space or manifold to define the notion of a small stack of groupoids over an étale topological or differentiable stack. We then provide a construction analogous to the étalé space construction in this context, establishing an equivalence of 2-categories between small stacks over an étale stack and local homeomorphisms over it. We go on to characterize small sheaves and gerbes. We show that ineffective data of étale stacks is completely described by the theory of small gerbes. Furthermore, it is shown that étale stacks (and in particular orbifolds) induce a small gerbe over their effective part, and all gerbes arise in this way. It follows that ineffective orbifolds, sometimes called non-reduced orbifolds, encode a canonical gerbe over their effective (or reduced) part. For nice enough classes of maps, for instance submersions, we show that étale stacks are equivalent to a 2-category of gerbed effective étale stacks. Along the way, we also prove that the 2-category of topoi is a full reflective sub-2-category of localic stacks.

math.AT↗

arXiv2012

Compactly Generated Stacks: A Cartesian Closed Theory of Topological Stacks

A convenient bicategory of topological stacks is constructed which is both complete and Cartesian closed. This bicategory, called the bicategory of compactly generated stacks, is the analogue of classical topological stacks, but for a different Grothendieck topology. In fact, there is an equivalence of bicategories between compactly generated stacks and those classical topological stacks which admit locally compact Hausdorff atlases. Compactly generated stacks are also equivalent to a bicategory of topological groupoids and principal bundles, just as in the classical case. If a classical topological stack and a compactly generated stack have a presentation by the same topological groupoid, then they restrict to the same stack over locally compact Hausdorff spaces and are homotopy equivalent.

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