arXiv subjects

Timothy Logvinenko

Publications and source records attributed to Timothy Logvinenko.

17 recordsLinked to original sources

arXiv2025

The Hochschild homology of a noncommutative symmetric quotient stack

We prove an orbifold type decomposition theorem for the Hochschild homology of the symmetric powers of a small DG category $\mathcal{A}$. In noncommutative geometry, these can be viewed as the noncommutative symmetric quotient stacks of $\mathcal{A}$. We use this decomposition to show that the total Hochschild homology of the symmetric powers of $\mathcal{A}$ is isomorphic to the symmetric algebra $S^*(\mathrm{HH}_\bullet(\mathcal{A}) \otimes t \mathbb{k}[t])$. Our methods are explicit - we construct mutually inverse homotopy equivalences of the standard Hochschild complexes involved. These explicit maps are then used to induce from the symmetric algebra onto the total Hochschild homology the structures of the Fock space for the Heisenberg algebra of $\mathcal{A}$, of a Hopf algebra, and of a free $\lambda$-ring generated by $\mathrm{HH}_\bullet(\mathcal{A})$.

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arXiv2025

The Heisenberg algebra of a vector space and Hochschild homology

For any noncommutative smooth and proper variety we construct three actions of the Heisenberg algebra on the total Hochschild homology of its symmetric quotient stacks. One is defined algebraically using the orbifold decomposition of Hochschild homology. One decategorifies the 2-categorical Heisenberg action of Gyenge-Koppensteiner-Logvinenko. One is defined representation theoretically via explicit operators intrinsic to the symmetric quotient stacks. We then show all three to coincide, and thus give alternative descriptions of one natural action. For ordinary commutative varities, we give a fourth, geometrical description by correspondences similar to those used by Grojnowski and Nakajima for the Hilbert schemes of points on surfaces.

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arXiv2023

Unbounded twisted complexes

We define unbounded twisted complexes and bicomplexes generalising the notion of a (bounded) twisted complex over a DG category [BK90]. These need to be considered relative to another DG category $B$ admitting countable direct sums and shifts. The resulting DG category of unbounded twisted complexes has a fully faithful convolution functor into Mod-$B$ which filters through $B$ if the latter admits change of differential. As an application, we rewrite definitions of $A_{\infty}$-structures in terms of twisted complexes to make them work in an arbitrary monoidal DG category or a DG bicategory.

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arXiv2023

$A_{\infty}$-structures in monoidal DG categories and strong homotopy unitality

We define $A_{\infty}$-structures -- algebras, coalgebras, modules, and comodules -- in an arbitrary monoidal DG category or bicategory by rewriting their definitions in terms of unbounded twisted complexes. We develop new notions of strong homotopy unitality and bimodule homotopy unitality to work in this level of generality. For a strong homotopy unital $A_{\infty}$-algebra we construct Free-Forgetful homotopy adjunction, its Kleisli category, and its derived category of modules. Analogous constructions for $A_{\infty}$-coalgebras require bicomodule homotopy counitality. We define homotopy adjunction for $A_{\infty}$-algebra and $A_{\infty}$-coalgebra and show such pair to be derived module-comodule equivalent. As an application, we obtain the notions of an $A_{\infty}$-monad and of an enhanced exact monad. We also show that for any adjoint triple $(L,F,R)$ of functors between enhanced triangulated categories the adjunction monad $RF$ and the adjunction comonad $LF$ are derived module-comodule equivalent.

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arXiv2021

The Heisenberg category of a category

Starting with a k-linear or DG category admitting a (homotopy) Serre functor, we construct a k-linear or DG 2-category categorifying the Heisenberg algebra of the numerical K-group of the original category. We also define a 2-categorical analogue of the Fock space representation of the Heisenberg algebra. Our construction generalises and unifies various categorical Heisenberg algebra actions appearing in the literature. In particular, we give a full categorical enhancement of the action on derived categories of symmetric quotient stacks introduced by Krug, which itself categorifies a Heisenberg algebra action proposed by Grojnowski.

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arXiv2019

$\mathbb{P}^n$-functors

We propose a new theory of (non-split) P^n-functors. These are F: A -> B for which the adjunction monad RF is a repeated extension of Id_A by powers of an autoequivalence H and three conditions are satisfied: the monad condition, the adjoints condition, and the highest degree term condition. This unifies and extends the two earlier notions of spherical functors and split P^n-functors. We construct the P-twist of such F and prove it to be an autoequivalence. We then give a criterion for F to be a P^n-functor which is stronger than the definition but much easier to check in practice. It involves only two conditions: the strong monad condition and the weak adjoints condition. For split P^n-functors, we prove Segal's conjecture on their relation to spherical functors. Finally, we give four examples of non-split P^n-functors: spherical functors, extensions by zero, cyclic covers, and family P-twists. For the latter, we show the P-twist to be the derived monodromy of associated Mukai flop, the so-called `flop-flop = twist' formula.

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arXiv2017

On uniqueness of P-twists

We prove that for any $\mathbb{P}^n$-functor all the convolutions (double cones) of the three-term complex $FHR \xrightarrow{\psi} FR \xrightarrow{tr} Id$ defining its $\mathbb{P}$-twist are isomorphic. We also introduce a new notion of a non-split $\mathbb{P}^n$-functor.

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arXiv2016

Bar category of modules and homotopy adjunction for tensor functors

Given a DG-category A we introduce the bar category of modules Modbar(A). It is a DG-enhancement of the derived category D(A) of A which is isomorphic to the category of DG A-modules with A-infinity morphisms between them. However, it is defined intrinsically in the language of DG-categories and requires no complex machinery or sign conventions of A-infinity categories. We define for these bar categories Tensor and Hom bifunctors, dualisation functors, and a convolution of twisted complexes. The intended application is to working with DG-bimodules as enhancements of exact functors between triangulated categories. As a demonstration we develop homotopy adjunction theory for tensor functors between derived categories of DG-categories. It allows us to show in an enhanced setting that given a functor F with left and right adjoints L and R the functorial complex $FR \rightarrow FRFR \rightarrow FR \rightarrow Id$ lifts to a canonical twisted complex whose convolution is the square of the spherical twist of F. We then write down four induced functorial Postnikov towers computing this convolution.

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arXiv2013

Spherical DG-functors

For two DG-categories A and B we define the notion of a spherical Morita quasi-functor A -> B. We construct its associated autoequivalences: the twist T of D(B) and the co-twist F of D(A). We give powerful sufficiency criteria for a quasi-functor to be spherical and for the twists associated to a collection of spherical quasi-functors to braid. Using the framework of DG-enhanced triangulated categories, we translate all of the above to Fourier-Mukai transforms between the derived categories of algebraic varieties. This is a broad generalisation of the results on spherical objects in [ST01] and on spherical functors in [Ann07]. In fact, this paper replaces [Ann07], which has a fatal gap in the proof of its main theorem. Though conceptually correct, the proof was impossible to fix within the framework of triangulated categories.

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arXiv2012

Derived Reid's recipe for abelian subgroups of SL3(C)

For any finite subgroup G in SL3(C), work of Bridgeland-King-Reid constructs an equivalence between the G-equivariant derived category of C^3 and the derived category of the crepant resolution Y = G-Hilb(C^3) of C^3/G. When G is abelian we show that this equivalence gives a natural correspondence between irreducible representations of G and certain sheaves on exceptional subvarieties of Y, thereby extending the McKay correspondence from two to three dimensions. This categorifies Reid's recipe and extends earlier work from [CL09] and [Log10] which dealt only with the case when C^3/G has one isolated singularity.

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arXiv2010

Orthogonally spherical objects and spherical fibrations

We introduce a relative version of the spherical objects of Seidel and Thomas. Define an object E in the derived category D(Z x X) to be spherical over Z if the corresponding functor from D(Z) to D(X) gives rise to autoequivalences of D(Z) and D(X) in a certain natural way. Most known examples come from subschemes of X fibred over Z. This categorifies to the notion of an object of D(Z x X) orthogonal over Z. We prove that such an object is spherical over Z if and only if it has certain cohomological properties similar to those in the original definition of a spherical object. We then interpret this geometrically in the case when our objects are actual flat fibrations in X over Z.

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arXiv2010

On adjunctions for Fourier-Mukai transforms

We show that the adjunction counits of a Fourier-Mukai transform $\Phi$ from $D(X_1)$ to $D(X_2)$ arise from maps of the kernels of the corresponding Fourier-Mukai transforms. In a very general setting of proper separable schemes of finite type over a field we write down these maps of kernels explicitly -- facilitating the computation of the twist (the cone of an adjunction counit) of $\Phi$. We also give another description of these maps, better suited to computing cones if the kernel of $\Phi$ is a pushforward from a closed subscheme $Z$ of $X_1 \times X_2$. Moreover, we show that we can replace the condition of properness of the ambient spaces $X_1$ and $X_2$ by that of $Z$ being proper over them and still have this description apply as is. This can be used, for instance, to compute spherical twists on non-proper varieties directly and in full generality.

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arXiv2008

Natural G-Constellation Families

Let G be a finite subgroup of GL_n(C). G-constellations are a scheme-theoretic generalization of orbits of G in C^n. We study flat families of G-constellations parametrised by an arbitrary resolution of the quotient space C^n/G. We develop a geometrical naturality criterion for such families, and show that, for an abelian G, the number of the equivalence classes of these natural families is finite. The main intended application is the derived McKay correspondence.

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arXiv2008

Reid's recipe and derived categories

We prove two existing conjectures which describe the geometrical McKay correspondence for a finite abelian G in SL3(C) such that C^3/G has a single isolated singularity. We do it by studying the relation between the derived category mechanics of computing a certain Fourier-Mukai transform and a piece of toric combinatorics known as `Reid's recipe', effectively providing a categorification of the latter.

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arXiv2008

A derived approach to geometric McKay correspondence in dimension three

We propose a three dimensional generalization of the geometric McKay correspondence described by Gonzales-Sprinberg and Verdier in dimension two. We work it out in detail when G is abelian and C^3/G has a single isolated singularity. More precisely, we show that the Bridgeland-King-Reid derived category equivalence induces a natural geometric correspondence between irreducible representations of G and subschemes of the exceptional set of G-Hilb (C^3). This correspondence appears to be related to Reid's recipe.

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arXiv2008

Derived McKay correspondence via pure-sheaf transforms

In most cases where it had been shown to exist the derived McKay correspondence D(Y) --> D^G(C^n) can be written as a Fourier-Mukai transform which sends point sheaves of the crepant resolution Y to pure sheaves in D^G(C^n). We give a sufficient condition for an object of D^G(Y x C^n) to be the defining object of such a transform. We use it to construct the first example of the derived McKay correspondence for a non-projective crepant resolution of C^3/G. Along the way we extract some more geometric sense out of the Intersection Theorem and learn to explicitly compute theta-stable families of G-constellations and their direct transforms.

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arXiv2003

Families of G-constellations over resolutions of quotient singularities

Let G be a finite subgroup of GL_n(C). A study is made of the ways in which resolutions of the quotient space C^n / G can parametrise G-constellations, that is, G-regular finite length sheaves. These generalise G-clusters, which are used in the McKay correspondence to construct resolutions of orbifold singularities. A complete classification theorem is achieved, in which all the natural families of G-constellations are shown to correspond to certain finite sets of G-Weil divisors, which are a special sort of rational Weil divisor, introduced in this paper. Moreover, it is shown that the number of equivalence classes of such families is always finite. Explicit examples are computed throughout using toric geometry.

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