arXiv subjects

Frank Reidegeld

Publications and source records attributed to Frank Reidegeld.

9 recordsLinked to original sources

arXiv2020

A construction of $G_2$-manifolds from K3 surfaces with a $\mathbb{Z}^2_2$-action

A product of a K3 surface $S$ and a flat 3-dimensional torus $T^3$ is a manifold with holonomy $SU(2)$. Since $SU(2)$ is a subgroup of $G_2$, $S\times T^3$ carries a torsion-free $G_2$-structure. We assume that $S$ admits an action of $\mathbb{Z}^2_2$ with certain properties. There are several possibilities to extend this action to $S\times T^3$. A recent result of Joyce and Karigiannis allows us to resolve the singularities of $(S\times T^3)/\mathbb{Z}^2_2$ such that we obtain smooth $G_2$-manifolds. We classify the quotients $(S\times T^3)/\mathbb{Z}^2_2$ under certain restrictions and compute the Betti numbers of the corresponding $G_2$-manifolds. Moreover, we study a class of quotients by a non-abelian group. Several of our examples have new values of $(b^2,b^3)$.

math.DG↗

arXiv2018

K3 surfaces with a pair of commuting non-symplectic involutions

We study K3 surfaces with a pair of commuting involutions that are non-symplectic with respect to two anti-commuting complex structures that are determined by a hyper-Kähler metric. One motivation for this paper is the role of such $\mathbb{Z}^2_2$-actions for the construction of $G_2$-manifolds. We find a large class of smooth K3 surfaces with such pairs of involutions, but we also pay special attention to the case that the K3 surface has ADE-singularities. Therefore, we introduce a special class of non-symplectic involutions that are suitable for explicit calculations and find 320 examples of pairs of involutions that act on K3 surfaces with a great variety of singularities.

math.AG↗

arXiv2015

$G_2$-orbifolds from K3 surfaces with ADE-singularities

We construct compact $G_2$-orbifolds with ADE-singularities that carry exactly one parallel spinor. Our examples are related to certain quotients of $\mathbb{C}^2\times T^3$ that have been investigated in arXiv:hep-th/9812205. We shortly discuss the physical applications of our examples.

math.DG↗

arXiv2015

K3 surfaces with non-symplectic automorphisms of order three and Calabi-Yau orbifolds

Let S be a K3 surface that admits a non-symplectic automorphism $ρ$ of order 3. We divide $S\times \mathbb{P}^1$ by $ρ\timesψ$ where $ψ$ is an automorphism of order 3 of $\mathbb{P}^1$. There exists a threefold ramified cover of a partial crepant resolution of the quotient that is a Calabi-Yau orbifold. We compute the Euler characteristic of our examples and obtain values ranging from 30 to 219.

math.AG↗

arXiv2013

Exceptional holonomy on vector bundles with two-dimensional fibers

An SU(3)- or SU(1,2)-structure on a 6-dimensional manifold N^6 can be defined as a pair of a 2-form omega and a 3-form rho. We prove that any analytic SU(3)- or SU(1,2)-structure on N^6 with d omega^2 =0 can be extended to a parallel Spin(7)- or Spin_0(3,4)-structure Phi that is defined on the trivial disc bundle N^6\times B_epsilon(0) for a sufficiently small epsilon>0. Furthermore, we show by an example that Phi is not uniquely determined by (omega,rho) and discuss if our result can be generalized to non-trivial bundles.

math.DG↗

arXiv2013

G2-manifolds from K3 surfaces with non-symplectic automorphisms

We show that K3 surfaces with non-symplectic automorphisms of prime order can be used to construct new compact irreducible G2-manifolds. This technique was carried out in detail by Kovalev and Lee for non-symplectic involutions. We use Chen-Ruan orbifold cohomology to determine the Hodge diamonds of certain complex threefolds, which are the building blocks for this approach.

math.DG↗

arXiv2010

Exceptional holonomy and Einstein metrics constructed from Aloff-Wallach spaces

We investigate cohomogeneity-one metrics whose principal orbit is an Aloff-Wallach space SU(3)/U(1). In particular, we are interested in metrics whose holonomy is contained in Spin(7). Complete metrics of this kind which are not product metrics have exactly one singular orbit. We prove classification results for metrics on tubular neighborhoods of various singular orbits. Since the equation for the holonomy reduction has only few explicit solutions, we make use of power series techniques. In order to prove the convergence and the smoothness near the singular orbit, we apply methods developed by Eschenburg and Wang. As a by-product of these methods, we find many new examples of Einstein metrics of cohomogeneity one.

math.DG↗

arXiv2009

Special cohomogeneity one metrics with Q^111 or M^110 as principal orbit

We classify all cohomogeneity one manifolds with principal orbit Q^111=SU(2)^3/U(1)^2 or M^110=(SU(3) x SU(2))/(SU(2) x U(1)) whose holonomy is contained in Spin(7). Various metrics with different kinds of singular orbits can be constructed by our methods. It turns out that the holonomy of our metrics is automatically SU(4) and that they are asymptotically conical. Moreover, we investigate the smoothness of the metrics at the singular orbit.

math.DG↗

arXiv2009

Spaces admitting homogeneous G2-structures

We classify all seven-dimensional spaces which admit a homogeneous cosymplectic G2-structure. The motivation for this classification is that each of these spaces is a possible principal orbit of a parallel Spin(7)-manifold of cohomogeneity one.

math.DG↗