arXiv subjects

Yoshinori Machida

Publications and source records attributed to Yoshinori Machida.

8 recordsLinked to original sources

arXiv2026

Prolongations of $(3, 6)$-distributions by singular curves

A subbundle of rank 3 in the tangent bundle over a 6-dimensional manifold is called a (3, 6)-distribution if its local sections generate the whole tangent bundle by taking their Lie brackets once. An integral curve of a distribution, whose velocity vectors belong to the distribution, can be a singular curve or an abnormal extremal in the sense of geometric control theory. In this paper, given a (3, 6)-distribution, we prolong it, using the data of singular curves, to a (3,5,7,8)-distribution, to a (3, 5, 7, 8, 9)-distribution which possesses additional pseudo-product structure respectively. Regarding also another prolongation to a (4, 6, 8)-distribution, we show the equivalence of the classification problems of those four classes of distributions obtained from (3, 6)-distributions, generalising the correspondences of those in B_3-SO(3,4)-homogeneous models.

math.DG↗

arXiv2025

Prolongation of $(8,15)$-Distribution of Type $F_4$ by Singular Curves

Cartan gives the model of $(8, 15)$-distribution with the exceptional simple Lie algebra $F_4$ as its symmetry algebra in his paper (1893), which is published one year before his thesis. In the present paper, we study abnormal extremals (singular curves) of Cartan's model from viewpoints of sub-Riemannian geometry and geometric control theory.Then we construct the prolongation of Cartan's model based on the data related to its singular curves, and obtain the nilpotent graded Lie algebra which is isomorphic to the negative part of the graded Lie algebra $F_4$.

math.DG↗

arXiv2024

Singular curves of hyperbolic $(4, 7)$-distributions of type $C_3$

A distribution of rank $4$ on a $7$-dimensional manifold is called a $(4, 7)$-distribution if its local sections generate the whole tangent space by taking Lie brackets once. Singular curves of $(4, 7)$-distributions are studied in this paper. In particular the class of hyperbolic $(4, 7)$-distributions of type $C_3$ is introduced and singular curves are completely described via prolongations for them.

math.DG↗

arXiv2021

Extrinsic Geometry and Linear Differential Equations

We give a unified method for the general equivalence problem of extrinsic geometry, on the basis of our formulation of a general extrinsic geometry as that of an osculating map $φ\colon (M,\mathfrak f) \to L/L^0 \subset \operatorname{Flag}(V,ϕ)$ from a filtered manifold $(M,\mathfrak f)$ to a homogeneous space $L/L^0$ in a flag variety $\operatorname{Flag}(V,ϕ)$, where $L$ is a finite-dimensional Lie group and $L^0$ its closed subgroup. We establish an algorithm to obtain the complete systems of invariants for the osculating maps which satisfy the reasonable regularity condition of constant symbol of type $(\mathfrak g_-, \operatorname{gr} V, L)$. We show the categorical isomorphism between the extrinsic geometries in flag varieties and the (weighted) involutive systems of linear differential equations of finite type. Therefore we also obtain a complete system of invariants for a general involutive systems of linear differential equations of finite type and of constant symbol. The invariants of an osculating map (or an involutive system of linear differential equations) are proved to be controlled by the cohomology group $H^1_+(\mathfrak g_-, \mathfrak l / \bar{\mathfrak g})$ which is defined algebraically from the symbol of the osculating map (resp. involutive system), and which, in many cases (in particular, if the symbol is associated with a simple Lie algebra and its irreducible representation), can be computed by the algebraic harmonic theory, and the vanishing of which gives rigidity theorems in various concrete geometries. We also extend the theory to the case when $L$ is infinite dimensional.

math.DG↗

arXiv2017

Generalization of Schlafli formula to the volume of a spherically faced simplex

We present two identities (contiguity relation and variation formula) concerning the volume of a spherically faced simplex in the Euclidean space. These identities are described in terms of Cayley-Menger determinants and their differentials involved with hypersphere arrangements. They are derived as a limit of fundamental identities for hypergeometric integrals.

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arXiv2017

Hypergeometric integrals associated with hypersphere arrangements and Cayley-Menger determinants

The n-dimensional hypergeometric integrals associated with a hypersphere arrangement are formulated by the pairing of n-dimensional twisted cohomology and its dual. Under the condition of general position there are stated some results which concern an explicit representation of the standard form by a special (NBC) basis of the twisted cohomology, the variational formula of the corresponding integral in terms of special invariant 1-forms written by Cayley-Menger minor determinants. Gauss-Manin connection is also formulated and is explicitly presented in two simplest cases.

math.DG↗

arXiv2015

Monge-Ampère Systems with Lagrangian Pairs

The classes of Monge-Ampère systems, decomposable and bi-decomposable Monge-Ampère systems, including equations for improper affine spheres and hypersurfaces of constant Gauss-Kronecker curvature are introduced. They are studied by the clear geometric setting of Lagrangian contact structures, based on the existence of Lagrangian pairs in contact structures. We show that the Lagrangian pair is uniquely determined by such a bi-decomposable system up to the order, if the number of independent variables $\geq 3$. We remark that, in the case of three variables, each bi-decomposable system is generated by a non-degenerate three-form in the sense of Hitchin. It is shown that several classes of homogeneous Monge-Ampère systems with Lagrangian pairs arise naturally in various geometries. Moreover we establish the upper bounds on the symmetry dimensions of decomposable and bi-decomposable Monge-Ampère systems respectively in terms of the geometric structure and we show that these estimates are sharp (Proposition 4.2 and Theorem 5.3).

math.DG↗

arXiv2005

Singularities of improper affine spheres and surfaces of constant Gaussian curvature

We study the equation for improper (parabolic) affine spheres from the view point of contact geometry and provide the generic classification of singularities appearing in geometric solutions to the equation as well as their duals. We also show the results for surfaces of constant Gaussian curvatureand for developable surfaces. In particular we confirm that generic singularities appearing in such a surface are just cuspidal edges and swallowtails.

math.DG↗