arXiv subjects

Eyup Yalcinkaya

Publications and source records attributed to Eyup Yalcinkaya.

4 recordsLinked to original sources

arXiv2025

Deformations of Locally Conformal Spin(7) Instantons

We explore the deformation theory of instantons on locally conformal (LC) $Spin(7)$ manifolds. These structures, characterized by a non-parallel fundamental 4-form $Φ$ satisfying $dΦ= θ\wedge Φ$, represent a significant, yet geometrically constrained, class of non-integrable $G$-structures. We analyze the infinitesimal deformation complex for $Spin(7)$-instantons in this setting. Our primary contribution is the reformulation of the linearized deformation equations -- comprising the linearized instanton condition and a gauge-fixing term -- using a $t$-parameter family of Dirac operators. We demonstrate that the $t$-dependent torsion terms arising from the Lee form $θ$ cancel precisely. This unexpected simplification reveals that the deformation space $\mathcal{H}^1$ is governed entirely by the Levi-Civita geometry, effectively reducing the torsion-full problem to a more classical, torsion-free (Levi-Civita) setting. Using a Lichnerowicz-type rigidity theorem, we establish a general condition for an (LC) $Spin(7)$-instanton to be rigid (i.e., $\mathcal{H}^1 = \{0\}$). We apply this theory to the flat instanton ($A=0$) on known compact homogeneous (LC) $Spin(7)$ manifolds and conclude that the flat instanton on these spaces is non-rigid, thus possessing a non-trivial moduli space.

math.DG↗

arXiv2024

The 4-Planes of Spin(7) Manifolds

This paper investigates the geometric structures and properties of 8-dimensional manifolds with Spin(7)-holonomy. We focus on the characterization and implications of 4-planes within these manifolds, which are endowed with an almost symplectic structure compatible with the Spin(7)-structure. We provide a detailed analysis of the differential forms defining these structures, including the Cayley 4-form and its stabilization under the Spin(7) group actions. Furthermore, we explore the concept of mirror duality within the context of exceptional holonomy, elucidating the relationship between dual structures and their topological constraints. By examining the conditions under which mirror duality arises, we enhance the understanding of the interplay between Spin(7)-structures and symplectic geometry. This endeavor contributes to our deeper understanding of the intricate symmetries and topological properties of these remarkable manifolds.

math.DG↗

arXiv2024

Equivariant Principal Bundles over the 2-Sphere

In this paper, we introduce the classification of equivariant principal bundles over the 2-sphere. Isotropy representations provide tools for understanding the classification of equivariant principal bundles. We consider a $Γ$-equivariant principal $G$-bundle over $S^2$ with structural group $G$ a compact connected Lie group, and $Γ\subset SO(3)$ a finite group acting linearly on $S^2.$ We prove that the equivariant 1-skeleton $X \subset S^2$ over the singular set can be classified by means of representations of their isotropy representations. Then, we show that equivariant principal G-bundles over the $S^2 $ can be classified by a $Γ$-fixed set of homotopy classes of maps, and the underlying $G$-bundle $ξ$ over $S^2$ can be determined by first Chern class.

math.GT↗

arXiv2024

On Locally Conformal Spin(7) Structure

This article reveals a significant connection in geometry: when the Lee form $θ$ is normal to an almost Hermitian manifold $N$, it implies that $N$ possesses a nearly Kähler structure. Investigating locally conformally Spin(7) manifolds with 2-vector fields, our study provides a concise yet rigorous proof of this relationship.

math.DG↗