arXiv subjects

Kursat Sozer

Publications and source records attributed to Kursat Sozer.

5 recordsLinked to original sources

arXiv2026

Quantum invariants of flat 2-bundles over 3-manifolds

We construct a scalar invariant of flat principal 2-bundles over 3-manifolds, with structure 2-group $\mathcal{G}$, from an involutory Hopf algebra graded by $\mathcal{G}$. Expressing $\mathcal{G}$ in terms of a crossed module $\chi$ and using the classification of such 2-bundles via the classifying space $B\chi$, this amounts to constructing a homotopy invariant of maps from 3-manifolds to $B\chi$. The construction of the invariant relies on a combinatorial description of such maps by $\chi$-colored Heegaard diagrams. When the corresponding map to $B\chi$ is nullhomotopic or, equivalently, when the associated flat principal $\mathcal{G}$-bundle is trivializable, the invariant reduces to the Kuperberg invariant of the underlying 3-manifold.

math.GT↗

arXiv2024

Hopf crossed module (co)algebras

Given a crossed module $χ$, we introduce Hopf $χ$-(co)algebras which generalize Hopf algebras and Hopf group-(co)algebras. We interpret them as Hopf algebras in some symmetric monoidal category. We prove that their categories of representations are monoidal and $χ$-graded (meaning that both objects and morphisms have degrees which are related via $χ$).

math.QA↗

arXiv2024

3d TQFTs and 3-manifold invariants

This is an invited contribution to the 2nd edition of the Encyclopedia of Mathematical Physics. We give an overview of 3-dimensional topological quantum field theories (TQFTs) and the corresponding quantum invariants of 3-manifolds. We recall the main algebraic concepts and constructions, such as modular and spherical fusion categories, the Witten-Reshetikhin-Turaev and Turaev-Viro theories, and the relation between these two TQFTs. We also briefly discuss generalizations of these constructions by providing a (non-exhaustive) review of some recent works on 3-dimensional extended TQFTs, defect TQFTs, homotopy QFTs, and non-semisimple TQFTs.

math.GT↗

arXiv2023

Monoidal categories graded by crossed modules and 3-dimensional HQFTs

Given a crossed module $χ$, we introduce $χ$-graded monoidal categories and $χ$-fusion categories. We use spherical $χ$-fusion categories to construct (via the state sum method) 3-dimensional Homotopy Quantum Field Theories with target the classifying space $Bχ$ of the crossed module $χ$ (which is a homotopy 2-type).

math.GT↗

arXiv2021

Two-Dimensional Extended Homotopy Field Theories

We give another definition of two-dimensional extended homotopy field theories (E-HFTs) with aspherical targets and classify them. When the target of E-HFT is chosen to be a $K(G,1)$-space, we classify E-HFTs taking values in the symmetric monoidal bicategory of algebras, bimodules, and bimodule maps by certain Frobenius $G$-algebras called quasi-biangular $G$-algebras. As an application, for any discrete group $G$, we verify a special case of the $(G \times SO(2))$-structured cobordism hypothesis due to Lurie.

math.GT↗