CyberSec Research

We establish a quantitative relationship between mixed cohomology classes and the geometric complexity of cohomologically calibrated metric connections with totally skew torsion on product manifolds. Extending the results of Pigazzini--Toda (2025), we show that the dimension of the off-diagonal curvature subspace of a connection $\nabla^C$ is bounded below by the sum of tensor ranks of the mixed K\"unneth components of its calibration class. The bound depends only on the mixed class $[\omega]_{\mathrm{mixed}}\in H^3(M;\mathbb{R})$, hence is topological and independent of the chosen product metric. This provides a computational criterion for geometric complexity and quantifies the interaction between topology and curvature, yielding a quantified version of ``forced irreducibility'' via the dimension of $\mathfrak{hol}_p^{\mathrm{off}}(\nabla^C)$.

We prove the conjecture of James W. Cannon and Gregory R. Conner that the fundamental group of the Griffiths double cone space is isomorphic to that of the harmonic archipelago. From this and earlier work in this area, we conclude that the isomorphism class of these groups is quite large and includes groups with a great variety of descriptions.

This work develops a comprehensive algebraic model for rational stable parametrized homotopy theory over arbitrary base spaces. Building on the simplicial analogue of the foundational framework of May-Sigurdsson for parametrized spectra, and the homotopy theory of complete differential graded Lie algebras, we construct an explicit sequence of Quillen equivalences that translate the homotopy theory of rational spectra of retractive simplicial sets into the purely algebraic framework of complete differential graded modules over the completed universal enveloping algebra $\widehat{UL}$ of a Lie model $L$ of the base simplicial set $B$. Explicitly, there is a sequence of Quillen adjunctions $$ \mathbf{Sp}_B \leftrightarrows \mathbf{Sp}_L \leftrightarrows \mathbf{Sp}_{\widehat{UL}}^0 \leftrightarrows \mathbf{cdgm}_{\widehat{UL}} $$ which induces a natural, strong monoidal equivalence of categories $$ {\rm Ho}\,\mathbf{Sp}_B^{\Bbb Q}\cong {\rm Ho}\, \mathbf{cdgm}_{\widehat{UL}}. $$ This equivalence is highly effective in practice as it provides direct computational access to invariants of simplicial spectra by translating them into homotopy invariants of $\widehat{UL}$-modules. Here $\mathbf{Sp}_B$ denotes the stable model category of spectra of retractive simplicial sets over $B$, $\mathbf{Sp}_L$ denotes the stable model category of spectra of retractive complete differential graded Lie algebras over $L$, $\mathbf{Sp}_{\widehat{UL}}^0$ denotes the stable model category of connected $\widehat{UL}$-module spectra, and $\mathbf{cdgm}_{\widehat{UL}}$ denotes the category of complete differential graded $\widehat{UL}$-modules.

We compute the cohomology of the quotient algebra $\mathcal{A}(2)$ of the $\mathbb{R}$-motivic dual Steenrod algebra. We do so by running a $\rho$-Bockstein spectral sequence whose input is the cohomology of $\mathbb{C}$-motivic $\mathcal{A}(2)$. The purpose of our computation is that the cohomology of $\mathcal{A}(2)$ is the input to an Adams spectral sequence of a hypothetical $\mathbb{R}$-motivic modular forms spectrum. This Adams spectral sequence computes the homotopy groups of such an $\mathbb{R}$-motivic modular forms spectrum, which in turn can be used to make inferences about the homotopy groups of the $\mathbb{R}$-motivic sphere spectrum and eventually about the classical stable stems.

The persistence diagram is a central object in the study of persistent homology and has also been investigated in the context of random topology. The more recent notion of the verbose diagram (a.k.a. verbose barcode) is a refinement of the persistence diagram that is obtained by incorporating ephemeral persistence features as extra points along the diagonal. In this work, we initiate the study of random verbose diagrams. We establish a strong law of large numbers for verbose diagrams as a random point cloud grows in size -- that is, we prove the existence of a limiting verbose diagram, viewed as a measure on the half-plane on and above the diagonal. Also, we characterize its support and compute its total mass. Along the way, we extend the notion of the persistent Betti number, reveal the relation between this extended notion and the verbose diagram (which is an extension of the fundamental lemma of persistent homology), and establish results on the asymptotic behavior of the extended persistent Betti numbers. This work extends the main results of the work by Hiraoka, Shirai, and Trinh and its sequel by Shirai and Suzaki to the setting of verbose diagrams.

We investigate homological stability for the space of sections of Fano fibrations over curves in the context of weak approximation, and establish it for projective bundles, as well as for conic and quadric surface bundles over curves.

In this paper, we study equivariant Hurewicz fibrations, obtain their internal characteristics, and prove theorems on relationship between equivariant fibrations and fibrations generated by them. Local and global properties of equivariant fibrations are examined. An equivariant analog of the Hurewicz theorem on passing from local fibrations to global fibrations is proved. A classification of equivariant fibrations with the property of uniqueness of a covering path is given.

We show that isomorphism classes $[\mathcal{A}]$ of flat $q\times q$ matrix bundles $\mathcal{A}$ (or projectively flat rank-$q$ complex vector bundles $\mathcal{E}$) on a pro-torus $\mathbb{T}$ are in bijective correspondence with the \v{C}ech cohomology group $H^2(\mathbb{T},\mu_q:=\text{$q^{th}$ roots of unity})$ (respectively $H^2(\mathbb{Z})$) via the image of $[A]\in H^1(\mathbb{T},PGL(q,\mathcal{C}_{\mathbb{T}}))$ through $H^1(\mathbb{T},PGL(q,\mathcal{C}_{\mathbb{T}}))\xrightarrow{\quad}H^2(\mathbb{T},\mu(q,\mathcal{C}_{\mathbb{T}}))$ (respectively the first Chern class $c_1(\mathcal{E})$). This is in the spirit of Auslander-Szczarba's result identifying real flat bundles on the torus with their first two Stiefel-Whitney classes, and contrasts with classifying spaces $B\Gamma$ of compact Lie groups $\Gamma$ (as opposed to $\mathbb{T}^n\cong B\mathbb{Z}^n$), on which flat non-trivial vector bundles abound. The discussion both recovers the Disney-Elliott-Kumjian-Raeburn classification of rational non-commutative tori $\mathbb{T}^n_{\theta}$ with a different, bundle-theoretic proof, and sheds some light on the connection between topological invariants associated to $\mathbb{T}^2_{\theta}$, $\theta\in\mathbb{Q}$ by Rieffel and respectively H{\o}egh-Krohn-Skjelbred.

We prove the Derived Mapping Space Lemma, which generalizes the central theorem of Cisinski's work on calculus of fractions for $\infty$-categories, and allows us to provide a unified framework for analyzing mapping spaces in localizations of ($\infty$-)categories. As an application, we give a sufficient condition for when a cubical or simplicial category is the localization of its underlying category at homotopy equivalences.

We show that any action of a finite group on a finitely presentable group arises as the action of the group of self-homotopy equivalences of a space on its fundamental group. In doing so, we prove that any finite connected (abstract) simplicial complex $\mathbf{K}$ can be rigidified -- meaning it can be perturbed in a way that reduces the full automorphism group to any subgroup -- while preserving the homotopy type of the geometric realization $| \mathbf{K} |$.

Let $\mathscr A$ be the Steenrod algebra over the field of characteristic two, $\mathbb F_2.$ Denote by $GL(q)$ the general linear group of rank $q$ over $\mathbb F_2.$ The algebraic transfer, introduced by W. Singer [Math. Z. 202 (1989), 493-523], is a rather effective tool for unraveling the intricate structure of the (mod-2) cohomology of the Steenrod algebra, ${\rm Ext}_{\mathscr A}^{q,*}(\mathbb F_2, \mathbb F_2).$ The Kameko homomorphism is one of the useful tools to study the dimension of the domain of the Singer transfer. Singer conjectured that the algebraic transfer is always a monomorphism, but this remains open for all homology degrees $q\geq 5.$ In this paper, by constructing a novel algorithm implemented in the computer algebra system OSCAR for computing $GL(q)$-invariants of the kernel of the Kameko homomorphism, we disprove Singer's conjecture for bidegree $(6, 6+36).$

Let $M_{n,k}$ denote the homogeneous space $SO(2n) / U(k) \times SO(2n-2k) $. We study the endomorphisms of the rational cohomology algebra of $M_{n,k}$, where $n-k \neq k-1$.

Computing homology and cohomology is at the heart of many recent works and a key issue for topological data analysis. Among homological objects, homology generators are useful to locate or understand holes (especially for geometric objects). The present paper provides a characterization of the class of homology bases that are computed by standard algorithmic methods. The proof of this characterization relies on the Homological Discrete Vector Field, a combinatorial structure for computing homology, which encompasses several standard methods (persistent homology, tri-partitions, Smith Normal Form, discrete Morse theory). These results refine the combinatorial homology theory and provide novel ideas to gain more control over the computation of homology generators.

Many complex networks, ranging from social to biological systems, exhibit structural patterns consistent with an underlying hyperbolic geometry. Revealing the dimensionality of this latent space can disentangle the structural complexity of communities, impact efficient network navigation, and fundamentally shape connectivity and system behavior. We introduce a novel topological data analysis weighting scheme for graphs, based on chordless cycles, aimed at estimating the dimensionality of networks in a data-driven way. We further show that the resulting descriptors can effectively estimate network dimensionality using a neural network architecture trained in a synthetic graph database constructed for this purpose, which does not need retraining to transfer effectively to real-world networks. Thus, by combining cycle-aware filtrations, algebraic topology, and machine learning, our approach provides a robust and effective method for uncovering the hidden geometry of complex networks and guiding accurate modeling and low-dimensional embedding.

Our work investigates the action of primitive Milnor operations $St^{\Delta_i}$ on the Dickson algebra $D_n$ over $\mathbb{F}_p$, building upon a foundational formula by Nguyen Sum [3]. Our central contribution is the introduction of a normalized operator, $\delta_i$, by factoring out the ubiquitous invariant $Q_{n, 0}$. This normalization transforms $St^{\Delta_i}$ into a true derivation on the localized Dickson algebra, thereby establishing an elegant differential framework. This framework yields two new significant results: first, a closed-form formula for all higher iterates of the operator, revealing a strong factorial-based vanishing criterion for iterates of order $\geq p$. Second, the discovery of a normalized coordinate system where the action has constant coefficients. This latter insight reduces the problem of computing the associated Margolis homology to a standard Koszul complex computation, in direct analogy with a recent result by Ngo Anh Tuan [4]. As further consequences, we also construct a large family of kernel elements and describe the global structure of the action.

For an ample groupoid with torsion-free stabilizers, we construct a Chern character map going from the domain of the Baum-Connes assembly map of G to the groupoid homology groups of G with rational coefficients. As a main application, assuming the (rational) Baum-Connes conjecture, we prove the rational form of Matui's HK conjecture, i.e., we show that the operator K-groups of the groupoid C*-algebra are rationally isomorphic to the periodicized groupoid homology groups. Our construction hinges on the recent $\infty$-categorical viewpoint on bivariant K-theory, and does not rely on typical noncommutative geometry tools such as the Chern-Connes character and the periodic cyclic homology of smooth algebras. We also present applications to the homology of hyperbolic dynamical systems, the homology of topological full groups, the homotopy type of the algebraic K-theory spectrum of ample groupoids, and the Elliott invariant of classifiable C*-algebras.

We define a class of smashing localisations which we call compactly central, and classify compactly central localisations of $Sp_{(p)}$ and of $Sp$. Our main result is that $L_n^f$ is a compactly central localisation. A map $\alpha: 1 \to A$ in a presentably symmetric monoidal $\infty$-category $\mathscr{C}$ is central if there exists a homotopy $\alpha \otimes id_A \simeq id_A \otimes \alpha: A \to A \otimes A$. A central map $\alpha$ can be used to produce a smashing localisation $L_\alpha$ of $\mathscr{C}$, because the free $\mathbb{E}_1$ algebra on the $\mathbb{E}_0$ algebra $\alpha$ is an idempotent commutative algebra. When both the monoidal unit and $A$ are compact, we call $L_\alpha$ compactly central. We show that when $\mathscr{C}$ is (compactly generated) rigid, all compactly central localisations are finite in the sense of Miller. Not all finite localisations of $Sp$ are compactly central. To exhibit $L_n^f$ as compactly central, we determine properties of the $K(n)$-homology of a map between $p$-local finite spectra which ensure that some tensor power of the map is central.

A refined transfer is defined for the purpose of defining a refined version of the families torsion of Dwyer, Weiss, and Williams.