arXiv subjects

Dadi Ni

Publications and source records attributed to Dadi Ni.

8 recordsLinked to original sources

arXiv2026

Affine deformations of cotangent groupoids

We study affine deformations of the cotangent groupoid $T^*\mathcal{G} \rightrightarrows A^*$, governed by a one-form $\gamma\in\Omega^1(\mathcal G^{(2)})$, and characterize the conditions on $\gamma$ under which this construction is valid. We show that these deformations arise naturally from $\mathbb{S}^1$-central extensions of Lie groupoids via symplectic reduction, and identify the reduced symplectic form as a multiplicative magnetic form. In particular, for Kac-Moody extensions, this construction yields nontrivial deformations of quotient stacks and $\mathbb{S}^1$-gerbes.

math.SG↗

arXiv2026

An Explicit Construction of $\mathbb{S}^1$-Gerbes over the Stack $[G/G]$

For a compact and connected Lie group $G$, we present an explicit construction of an $\mathbb{S}^1$-gerbe over the differentiable stack $[G/G]$ in the framework of $\mathbb{S}^1$-central extensions of Lie groupoids. This gives a complete proof of the construction outlined earlier by Behrend--Xu--Zhang, together with an explicit proof of the differential-form identity stated there without proof. In particular, when $G$ is compact, simple, and simply connected, the Dixmier--Douady class of the resulting gerbe is the canonical generator of ${\rm H}^3_G(G,\mathbb Z)$.

math.SG↗

arXiv2025

Infinitesimal deformations of Lie algebroid pairs

We study infinitesimal deformations of Lie algebroid pairs in the category of smooth manifolds enriched with a local Artinian algebra. Given a Lie algebroid pair $(L,A)$, i.e. a Lie algebroid $L$ together with a Lie subalgebroid $A$, we investigate isomorphism classes of infinitesimal deformations of $(L,A)$ modulo automorphisms from exponentials of derivations of $L$ and those from the exponentials of inner derivations of $L$, respectively. For the associated two deformation functors, we find the associated governing $L_\infty$-algebras in the sense of extended deformation theory. Furthermore, when $(L,A)$ is a matched Lie pair, i.e. the quotient $L/A$ is also a Lie subalgebroid of $L$, we investigate isomorphism classes of infinitesimal deformations modulo automorphisms from exponentials of derivations along the normal direction $L/A$. The extended deformation theory of the associated deformation functor recovers the formal deformation theory of complex structures and that of transversely holomorphic foliations.

math.DG↗

arXiv2025

Atiyah Classes in the Context of Generalized Complex Geometry

In analogy to the classical holomorphic setting, Lang, Jia and Liu introduced the notion of the Atiyah class for a generalized holomorphic vector bundle using three different approaches: leveraging $\rm{\check{C}}$ech cohomology, employing the first jet short exact sequence, and adopting the perspective of Lie algebroid pairs. The purpose of this note is to establish the equivalence among these diverse definitions of the Atiyah class.

math.DG↗

arXiv2025

Atiyah constructions for Lie algebroid connections on fiber bundles

To address the need for a unified framework that incorporates Lie algebroid connections on both vector and principal bundles, this paper investigates a generalized Atiyah algebroid structure and its short exact sequence. Building on this generalization, we describe Atiyah-type extensions and sequences that represent Atiyah classes through three explicit constructions designed to encode Lie algebroid connections compatible with specified sub-structures. As illustrative examples, we work out an enriched Atiyah algebroid construct, providing a systematic tool to characterize certain key properties of holomorphic connections and invariant connections.

math.DG↗

arXiv2025

Hyperk\"ahler structures on leaves of hyper-Lie Poisson manifolds

Due to its rich structure and close connection with gauge theory, hyperk\"ahler manifolds have attracted increasing interest. Using infinite dimensional hyperk\"ahler reduction, Kronheimer proved that certain adjoint orbits of complexified semisimple Lie algebras admits hyperk\"ahler structures. Later on, Xu obtained a proof for the existence of hyperk\"ahler structures on adjoint orbits of $\mathfrak{sl}(2,\mathbb{C})$ from the viewpoint of symplectic geometry. This paper aims to thoroughly investigate and elucidate the key differences as well as the underlying connections between two distinct construction methods.

math.DG↗

arXiv2022

Internal symmetry of the $L_{\leqslant 3}$ algebra arising from a Lie pair

A Lie pair is an inclusion $A$ to $L$ of Lie algebroids over the same base manifold. In an earlier work, the third author with Bandiera, Sti\'{e}non, and Xu introduced a canonical $L_{\leqslant 3}$ algebra $\Gamma(\wedge^\bullet A^\vee \otimes L/A)$ whose unary bracket is the Chevalley-Eilenberg differential arising from every Lie pair $(L,A)$. In this note, we prove that to such a Lie pair there is an associated Lie algebra action by $\mathrm{Der}(L)$ on the $L_{\leqslant 3}$ algebra $\Gamma(\wedge^\bullet A^\vee \otimes L/A)$. Here $\mathrm{Der}(L)$ is the space of derivations on the Lie algebroid $L$, or infinitesimal automorphisms of $L$. The said action gives rise to a larger scope of gauge equivalences of Maurer-Cartan elements in $\Gamma(\wedge^\bullet A^\vee \otimes L/A)$, and for this reason we elect to call the $\mathrm{Der}(L)$-action internal symmetry of $\Gamma(\wedge^\bullet A^\vee \otimes L/A)$.

math.DG↗

arXiv2021

Hopf algebras arising from dg manifolds

Let $(\mathcal{M}, Q)$ be a dg manifold. The space of vector fields with shifted degrees $(\mathcal{X}(\mathcal{M})[-1], L_Q)$ is a Lie algebra object in the homology category $\mathrm{H}((C^{\infty}_{\mathcal{M}},Q)\mathrm{-}\mathbf{mod})$ of dg modules over $(\mathcal{M},Q)$, the Atiyah class $α_{\mathcal{M}}$ being its Lie bracket. The triple $(\mathcal{X}(\mathcal{M})[-1], L_Q; α_{\mathcal{M}})$ is also a Lie algebra object in the Gabriel-Zisman homotopy category $Π((C^{\infty}_{\mathcal{M}},Q)\mathrm{-}\mathbf{mod})$. In this paper, we describe the universal enveloping algebra of $(\mathcal{X}(\mathcal{M})[-1], L_Q; α_{\mathcal{M}})$ and prove that it is a Hopf algebra object in $Π((C^{\infty}_{\mathcal{M}},Q)\mathrm{-}\mathbf{mod})$. As an application, we study Fedosov dg Lie algebroids and recover a result of Stiénon, Xu, and the second author on the Hopf algebra arising from a Lie pair.

math.DG↗