arXiv subjects

Kurando Baba

Publications and source records attributed to Kurando Baba.

13 recordsLinked to original sources

arXiv2026

Equifocal hypersurfaces in symmetric spaces of compact type and backward mean curvature flows

We first derive a formula for the mean curvature and the squared norm of the shape operator of equifocal hypersurfaces in simply-connected irreducible symmetric spaces of compact type. The formulas are given explicitly in terms of the tangential focal data of the equifocal hypersurfaces. Third, we study the backward mean curvature flow for equifocal hypersurfaces. The long-time existence of this flow for an equifocal hypersurface was established by Liu and Radeschi. We analyze the time evolution of the mean curvature and the squared norm of the shape operator along the long-time solution, thereby we generalize the result of Liu and Terng for isoparametric hypersurfaces in the sphere. Our analysis also gives an extension of Liu-Terng conjecture on the backward mean curvature flows in the sphere to the simply-connected irreducible symmetric space of compact type.

math.DG↗

arXiv2026

Moduli spaces of contact instantons on Sasakian 5-manifolds with transverse Calabi-Yau structures and orbifold K3 surfaces

We study anti-self-dual contact instantons on 5-dimensional Sasakian manifolds with transverse Calabi-Yau structures. In this case, the leaf space is a Calabi-Yau orbifold, and the moduli space of irreducible anti-self-dual contact instantons is a hyperkahler manifold. Using the singularity data of the leaf spaces, we prove that the transverse Levi-Civita connection gives an irreducible anti-self-dual contact instanton in the case when the leaf space is one of the 95 orbifold $K3$ surfaces classified by Reid. Moreover, we compute explicitly the complex dimension of the corresponding moduli spaces in all 95 cases.

math.DG↗

arXiv2025

Compact symmetric triads and symmetric triads with multiplicities

In this paper, we develop the theory of symmetric triads with multiplicities. First, we classify abstract symmetric triads with multiplicities. Second, we determine the symmetric triads with multiplicities corresponding to commutative compact symmetric triads. As applications, we give the classifications for commutative compact symmetric triads, which consist of two types depending on the choice of the equivalence relations.

math.DG↗

arXiv2024

Construction of special Lagrangian submanifolds of the Taub-NUT manifold and the Atiyah-Hitchin manifold

We construct special Lagrangian submanifolds of the Taub-NUT manifold and the Atiyah-Hitchin manifold by combining the generalized Legendre transform approach and the moment map technique. The generalized Legendre transform approach provides a formulation to construct hyperk\"ahler manifolds and can make their Calabi-Yau structures manifest. In this approach, the K\"ahler $2$-forms and the holomorphic volume forms can be written in terms of holomorphic coordinates, which are convenient to employ the moment map technique. This technique derives the condition that a submanifold in the Calabi-Yau manifold is special Lagrangian. For the Taub-NUT manifold and the Atiyah-Hitchin manifold, by the moment map technique, special Lagrangian submanifolds are obtained as a one-parameter family of the orbits corresponding to Hamiltonian action with respect to their K\"ahler 2-forms. The resultant special Lagrangian submanifolds have cohomogeneity-one symmetry. To demonstrate that our method is useful, we recover the conditions for the special Lagrangian submanifold of the Taub-NUT manifold which is invariant under the tri-holomorphic $U(1)$ symmetry. As new applications of our method, we construct special Lagrangian submanifolds of the Taub-NUT manifold and the Atiyah-Hitchin manifold which are invariant under the action of a Lie subgroup of $SO(3)$. In these constructions, our conditions for being special Lagrangian are expressed by ordinary differential equations (ODEs) with respect to the one-parameters. We numerically give solution curves for the ODEs which specify the special Lagrangian submanifolds for the above cases.

math-ph↗

arXiv2023

A Simons type condition for instability of $F$-Yang-Mills connections

$F$-Yang-Mills connections are critical points of $F$-Yang Mills functional on the space of connections of a principal fiber bundle, which is a generalization of Yang-Mills connections, $p$-Yang-Mills connections and exponential Yang-Mills connections and so on. Here, $F$ is a strictly increasing $C^{2}$-function. In this paper, we extend Simons theorem for an instability of Yang-Mills connections to $F$-Yang-Mills connections. We derive a sufficient condition that any non-flat, $F$-Yang-Mills connection over convex hypersurfaces in a Euclidean space is instable. In the sphere case, this condition is expressed by an inequality with respect to its dimension and a degree of the differential of the function $F$. The proofs of the results are given by extending Kobayashi-Ohnita-Takeuchi's calculation to $F$-Yang-Mills connections.

math.DG↗

arXiv2022

Revisiting Atiyah-Hitchin manifold in the generalized Legendre transform

We revisit construction of the Atiyah-Hitchin manifold in the generalized Legendre transform approach. This is originally studied by Ivanov and Rocek and is subsequently investigated more by Ionas, in the latter of which the explicit forms of the K\"ahler potential and the K\"ahler metric are calculated. There is a difference between the former and the latter. In the generalized Legendre transform approach, a K\"ahler potential is constructed from the contour integration of one function with holomorphic coordinates. The choice of the contour in the latter is different from the former's one, whose difference may yield a discrepancy in the K\"ahler potential and eventually in the K\"ahler metric. We show that the former only gives the real K\"ahler potential, which is consistent with its definition, while the latter yields the complex one. We derive the K\"ahler potential and the metric for the Atiyah-Hitchin manifold in terms of holomorphic coordinates for the contour considered by Ivanov and Ro\v{c}ek for the first time.

hep-th↗

arXiv2022

Double Satake diagrams and canonical forms in compact symmetric triads

In this paper, we first introduce the notion of double Satake diagrams for compact symmetric triads. In terms of this notion, we give an alternative proof for the classification theorem for compact symmetric triads, which was originally given by Toshihiko Matsuki. Secondly, we introduce the notion of canonical forms for compact symmetric triads, and prove the existence of canonical forms for compact simple symmetric triads. We also give some properties for canonical forms.

math.DG↗

arXiv2021

Calabi-Yau structure and Bargmann type transformation on the Cayley projective plane

Our purpose is to show the existence of a Calabi-Yau structure on the punctured cotangent bundle $T^{*}_{0}(P^2\mathbb{O})$ of the Cayley projective plane $P^{2}\mathbb{O}$ and to construct a Bargmann type transformation from a space of holomorphic functions on $T^{*}_{0}(P^2\mathbb{O})$ to $L_{2}$-space on $P^{2}\mathbb{O}$. The space of holomorphic functions corresponds to the Fock space in the case of the original Bargmann transformation. A K\"ahler structure on $T^{*}_{0}(P^{2}\mathbb{O})$ was shown by identifying it with a quadrics in the complex space $\mathbb{C}^{27}\backslash\{0\}$ and the natural symplectic form of the cotangent bundle $T^{*}_{0}(P^2\mathbb{O})$ is expressed as a K\"ahler form. Our method to construct the transformation is the pairing of polarizations, one is the natural Lagrangian foliation given by the projection map ${\bf q}:T^{*}_{0}(P^2\mathbb{O})\longrightarrow P^{2}\mathbb{O}$ and the polarization given by the K\"ahler structure. The transformation gives a quantization of the geodesic flow in terms of one parameter group of elliptic Fourier integral operators whose canonical relations are defined by the graph of the geodesic flow action at each time. It turn out that for the Cayley projective plane the results are not same with other cases of the original Bargmann transformation for Euclidean space, spheres and other projective spaces.

math.DG↗

arXiv2020

A duality between non-compact semisimple symmetric pairs and commutative compact semisimple symmetric triads and its general theory

The present paper investigates a natural generalization of the duality between Riemannian symmetric pairs of compact type and those of non-compact type \`a la \'E. Cartan. The main result of this paper is to construct an explicit description of a one-to-one correspondence between non-compact pseudo-Riemannian semisimple symmetric pairs and commutative compact semisimple symmetric triads, which is called the duality theorem. Further, we develop a general theory of the duality theorem.

math.RT↗

arXiv2017

Special Lagrangian submanifolds and cohomogeneity one actions on the complex projective space

We construct examples of cohomogeneity one special Lagrangian submanifolds in the cotangent bundle over the complex projective space, whose Calabi-Yau structure was given by Stenzel. For each example, we describe the condition of special Lagrangian as an ordinary differential equation. Our method is based on a moment map technique and the classification of cohomogeneity one actions on the complex projective space classified by Takagi.

math.DG↗

arXiv2015

Examples of austere orbits of the isotropy representations for semisimple pseudo-Riemannian symmetric spaces

Harvey-Lawson and Anciaux introduced the notion of austere submanifolds in pseudo-Riemannian geometry. We give an equivalent condition for an orbit of the isotropy representations for semisimple pseudo-Riemannian symmetric space to be an austere submanifold in a pseudo-sphere in terms of restricted root system theory with respect to Cartan subspaces. By using the condition we give examples of austere orbits.

math.DG↗

arXiv2014

Supersymmetry and Cotangent Bundle over Non-compact Exceptional Hermitian Symmetric Space

We construct N=2 supersymmetric nonlinear sigma models on the cotangent bundles over the non-compact exceptional Hermitian symmetric spaces M=E_{6(-14)}/SO(10)xU(1) and E_{7(-25)}/E_6xU(1). In order to construct them we use the projective superspace formalism which is an N=2 off-shell superfield formulation in four-dimensional space-time. This formalism allows us to obtain the explicit expression of N=2 supersymmetric nonlinear sigma models on the cotangent bundles over any Hermitian symmetric spaces in terms of the N=1 superfields, once the Kahler potentials of the base manifolds are obtained. We derive the N=1 supersymmetric nonlinear sigma models on the Kahler manifolds M. Then we extend them into the N=2 supersymmetric models with the use of the result in arXiv:1211.1537 developed in the projective superspace formalism. The resultant models are the N=2 supersymmetric nonlinear sigma models on the cotangent bundles over the Hermitian symmetric spaces M. In this work we complete constructing the cotangent bundles over all the compact and non-compact Hermitian symmetric spaces.

hep-th↗

arXiv2013

Local orbit types of the isotropy representations for semisimple pseudo-Riemannian symmetric spaces

We list up all the possible local orbit types of hyperbolic or elliptic orbits for the isotropy representations of semisimple pseudo-Riemannian symmetric spaces. It is key to give a recipe to determine the local orbit types of hyperbolic principal orbits by using three kind of restricted root systems and Satake diagrams associated with semisimple pseudo-Riemannian symmetric spaces.

math.DG↗