On the convex invariance in Finsler geometry

A Schwarz lemma for weakly Kähler-Finsler manifolds

In this paper, we first establish several theorems about the estimation of distance function on real and strongly convex complex Finsler manifolds and then obtain a Schwarz lemma from a strongly convex weakly Kähler-Finsler manifold into a strongly pseudoconvex complex Finsler manifold. As applications, we prove that a holomorphic mapping from a strongly convex weakly Kähler-Finsler manifold into a strongly pseudoconvex complex Finsler manifold is necessary constant under an extra condition. In particular, we prove that a holomorphic mapping from a complex Minkowski space into a strongly pseud…

Anisotropic conformal invariance of lightlike geodesics in pseudo-Finsler manifolds

In this paper, we prove that lightlike geodesics of a pseudo-Finsler manifold and its focal points are preserved up to reparametrization by anisotropic conformal changes, using the Chern connection and the anisotropic calculus and the fact that geodesics are critical points of the energy functional and Jacobi fields, the kernel of its index form. This result has applications to the study of Finsler spacetimes.

Finsler geodesics in the presence of a convex function and their applications

We obtain a result about the existence of only a finite number of geodesics between two fixed non-conjugate points in a Finsler manifold endowed with a convex function. We apply it to Randers and Zermelo metrics. As a by-product, we also get a result about the finiteness of the number of lightlike and timelike geodesics connecting an event to a line in a standard stationary spacetime.

On strongly convex projectively flat and dually flat complex Finsler metrics

In this paper, we prove that a strongly convex complex Finsler metric $F$ on a domain $D\subset\mathbb{C}^n$ is projectively flat (resp. dually flat) if and only if $F$ comes from a strongly convex complex Minkowski metric.

芬斯勒可度量化与测地线不变性

Finsler metrizabilities and geodesic invariance

该研究将芬斯勒可度量化问题转化为度量与角张量的测地线不变性问题，明确陀螺spray是具测地线不变角度量的最大类别，其关联标量函数不变性可提供spray的首次积分。

关于Finsler几何中广义投影Riemann曲率

On the Generalized Projective Riemann Curvature in Finsler Geometry

本文研究Finsler几何中广义投影Riemann曲率的性质，提出新的曲率特征化方法，揭示其在投影变换下的不变性及几何意义。

Riemannian-Finsler几何的全局研究

The global study of Riemannian-Finsler geometry

本文比较研究Riemannian与Finsler几何，探讨切点和共轭区域的差异，分析凸函数在Riemannian流形上的拓扑与微分结构及Finsler流形中的类比结果。

Dynamically convex Finsler metrics and $J$-holomorphic embedding of asymptotic cylinders

We explore the relationship between contact forms on $\mathbb S^3$ defined by Finsler metrics on $\mathbb S^2$ and the theory developed by H. Hofer, K. Wysocki and E. Zehnder in \cite{HWZ,HWZ1}. We show that a Finsler metric on $\mathbb S^2$ with curvature $K\geq 1$ and with all geodesic loops of length $>π$ is dynamically convex and hence it has either two or infinitely many closed geodesics. We also explain how to explicitly construct $J$-holomorphic embeddings of cylinders asymptotic to Reeb orbits of contact structures arising from Finsler metrics on $\mathbb S^2$ with K=1 thus complementi…

Convex trigonometry with applications to sub-Finsler geometry

A new convenient method of describing flat convex compact sets is proposed. It generalizes classical trigonometric functions $\sin$ and $\cos$. Apparently, this method may be very useful for explicit description of solutions of optimal control problems with two-dimensional control. Using this method a series of sub-Finsler problems with two-dimensional control lying in an arbitrary convex set $Ω$ is investigated. Namely, problems on the Heisenberg, Engel, and Cartan groups and also Grushin's and Martinet's cases are considered. A particular attention is paid to the case when $Ω$ is a polygon.

强凸 $C^0$-芬斯勒结构的磨光子光滑化

Mollifier smoothings of strongly convex $C^0$-Finsler structures

本研究针对强凸 $C^0$-芬斯勒结构构造两种磨光子光滑化，证明相关几何对象随参数趋于0时一致收敛到原结构的对应对象。

Monochromatic Finsler surfaces and a local ellipsoid characterization

We prove the following localized version of a classical ellipsoid characterization: Let $B\subset\mathbb R^3$ be convex body with a smooth strictly convex boundary and 0 in the interior, and suppose that there is an open set of planes through 0 such that all sections of $B$ by these planes are linearly equivalent. Then all these sections are ellipses and the corresponding part of $B$ is a part of an ellipsoid. We apply this to differential geometry of Finsler surfaces in normed spaces and show that in certain cases the intrinsic metric of a surface imposes restrictions on its extrinsic geometr…

Explicit formulae for geodesics in left invariant sub-Finsler problems on Heisenberg groups via convex trigonometry

In the present paper, we obtain explicit formulae for geodesics in some left-invariant sub-Finsler problems on Heisenberg groups $\mathbb{H}_{2n+1}$. Our main assumption is the following: the compact convex set of unit velocities at identity admits a generalization of spherical coordinates. This includes convex hulls and sums of coordinate 2-dimensional sets, all left-invariant sub-Riemannian structures on $\mathbb{H}_{2n+1}$, and unit balls in $L_p$-metric for $1\le p\le\infty$. In the last case, extremals are obtained in terms of incomplete Euler integral of the first kind.

On the generalization of theorems from Riemannian to Finsler Geometry I: Metric Theorems

A method to generalize results from Riemannian Geometry to Finsler geometry is presented. We use the method to generalize several results that involve only metric conditions. Between them we show that the topology induced by the Finsler structure is equivalent to the manifold topology, we provide a new proof of the Hopf-Rinow theorem in Finsler geometry and we prove the existence of the center of mass of a convex body when the non-symmetric distance function comes from a non-reversible Finsler function.

On the Berwald-Landsberg problem

Given a Finsler space (M,F), one can define natural average Riemannian metrics on M by averaging on the indicatrix I_x the fundamental tensor g of the Finsler function $F$. In this paper we determine explicitly the Levi-Civita connection for these average Riemannian metrics. We apply the result to the case when (M,F) is a Landsberg space. Using a particular averaging procedure, the invariance of the average metric along a homotopy in the space of Finsler structures over M is shown. As a consequence of such invariance, we prove that any C^5 regular Landsberg space is a Berwald space.

Rigidity of Busemann convex Finsler metrics

We prove that a Finsler metric is nonpositively curved in the sense of Busemann if and only if it is affinely equivalent to a Riemannian metric of nonpositive sectional curvature. In other terms, such Finsler metrics are precisely Berwald metrics of nonpositive flag curvature. In particular in dimension 2 every such metric is Riemannian or locally isometric to that of a normed plane. In the course of the proof we obtain new characterizations of Berwald metrics in terms of the so-called linear parallel transport.

Positively curved Finsler metrics on vector bundles

We construct a convex and strongly pseudoconvex Kobayashi positive Finsler metric on a vector bundle $E$ under the assumption that the symmetric power of the dual $S^kE^*$ has a Griffiths negative $L^2$-metric for some $k$. The proof relies on the negativity of direct image bundles and the Minkowski inequality for norms. As a corollary, we show that given a strongly pseudoconvex Kobayashi positive Finsler metric, one can upgrade to a \textit{convex} Finsler metric with the same property. We also give an extremal characterization of Kobayashi curvature for Finsler metrics.

Extremals for a series of sub-Finsler problems with 2-dimensional control via convex trigonometry

We consider a series of optimal control problems with 2-dimensional control lying in an arbitrary convex compact set $Ω$. The considered problems are well studied for the case when $Ω$ is a unit disc, but barely studied for arbitrary $Ω$. We derive extremals to these problems in general case by using machinery of convex trigonometry, which allows us to do this identically and independently on the shape of $Ω$. The paper describes geodesics in (i) the Finsler problem on the Lobachevsky hyperbolic plane; (ii) left-invariant sub-Finsler problems on all unimodular 3D Lie groups (SU(2), SL(2), SE(2…

Holomorphic invariant strongly pseudoconvex complex Finsler metrics

Let $B_n$ and $P_n$ be the unit ball and the unit polydisk in $\mathbb{C}^n$ with $n\geq 2$ respectively. Denote $\mbox{Aut}(B_n)$ and $\mbox{Aut}(P_n)$ the holomorphic automorphism group of $B_n$ and $P_n$ respectively. In this paper, we prove that $B_n$ admits no $\mbox{Aut}(B_n)$-invariant strongly pseudoconvex complex Finsler metric other than a constant multiple of the Poincar$\acute{\mbox{e}}$-Bergman metric, while $P_n$ admits infinite many $\mbox{Aut}(P_n)$-invariant complete strongly convex complex Finsler metrics other than the Bergman metric. The $\mbox{Aut}(P_n)$-invariant complex …

Harmonic symmetrization of convex sets and of Finsler structures, with applications to Hilbert geometry

David Hilbert discovered in 1895 an important metric that is canonically associated to any convex domain $Ω$ in the Euclidean (or projective) space. This metric is known to be Finslerian, and the usual proof assumes a certain degree of smoothness of the boundary of $Ω$ and refers to a theorem by Busemann and Mayer that produces the norm of a tangent vector from the distance function. In this paper, we develop a new approach for the study of the Hilbert metric where no differentiability is assumed. The approach exhibits the Hilbert metric on a domain as a symmetrization of a natural weak metric…

Funk and Hilbert geometries from the Finslerian Viewpoint

In 1929, Paul Funk and Ludwig Berwald gave a characterization of Hilbert geometries from the Finslerian viewpoint. They showed that a smooth Finsler metric in a convex bounded domain of $\mathbb{R}^n$ is the Hilbert geometry in that domain if and only if it is complete, if its geodesics are straight lines and if its flag curvature is equal to -1. The goal of this chapter is to explain these notions in details, to illustrate the relation between Hilbert geometry, Finsler geometry and the calculus of variations, and to prove the Funk-Berwald characterization Theorem.

The Structure Equations of a Complex Finsler Manifold

For a strongly pseudo-convex complex Finsler manifold M, a bundle U of adapted unitary frames is canonically defined. A non-linear Hermitian connection on U, invariant under local biholomorphic isometries, is given and it proved to be unique. By means of such connection, an absolute parallelism on U is determined and a new set of structure functions which generate all the isometric invariants of a Finsler metric is obtained. A pseudo-convex complex Finsler manifolds M, which admits a totally geodesic complex curve with a given constant holomorphic sectional curvature through any point and any …

Sub-Finsler Lie 群中的正规曲线：强凸范数的分支与多面体范数的面稳定性

Normal Curves in Sub-Finsler Lie Groups: Branching for Strongly Convex Norms and Face Stability for Polyhedral Norms

本文研究了 sub-Finsler Lie 群中的正规曲线，利用凸分析工具重新表述了 Pontryagin Maximum Principle，并证明了强凸范数下的分支现象以及多面体范数下控制的面稳定性。

李群上左不变强凸$C^0$-Finsler结构的Mollifier光滑化及极值曲线的收敛性

Mollifier smoothing of left-invariant strongly convex $C^0$-Finsler structures on Lie groups and convergence of extremals

该研究针对李群上的左不变强凸$C^0$-Finsler结构，提出左不变版本的mollifier光滑化方法，利用Pontryagin最大值原理证明了极值曲线的存在唯一性，以及光滑化后结构的极值曲线在紧区间上一致收敛于原结构的极值曲线。

A Toponogov type triangle comparison theorem in Finsler geometry

The aim of this article is to establish a Toponogov type triangle comparison theorem for Finsler manifolds, in the manner of radial curvature geometry. We consider the situation that the radial flag curvature is bounded below by the radial curvature function of a non-compact surface of revolution, the edge opposite to the base point is contained in a Berwald-like region, and that the Finsler metric is convex enough in the radial directions in that region.

凸射影曲面的极限与Finsler度量

Limits of Convex Projective Surfaces and Finsler Metrics

本文证明SL₃ℝ Hitchin分量中逃逸序列的迹函数增长率可由具有三角形单位球的Finsler度量描述，等价于并强化了Loftin猜想，且方法适用于渐近三次微分射线的表示序列，深化了对凸射影曲面模空间紧化的理解。

On electromagnetism and generalized energy-momentum tensor of the electromagnetic field in spaces with Finsler geometry

By using variational calculus and exterior derivative formalism, we proposed in two previous joint papers with S. Siparov a new geometric approach for electromagnetism in pseudo-Finsler spaces. In the present paper, we provide more details, especially regarding generalized currents, the domain of integration and gauge invariance. Also, for flat pseudo-Finsler spaces, we define a generalized energy-momentum tensor (consisting of two blocks), as the symmetrized Noether current corresponding to the invariance of the field Lagrangian with respect to spacetime translations. In curved spaces, one of…

二维射影 Finsler 度量中反射焦散线的尖点

On cusps of caustics by reflection in two dimensional projective Finsler metrics

本文研究射影 Finsler 度量下凸平面区域中的 Finsler 台球，证明经历固定反射次数的反射焦散线至少具有四个尖点，推广了欧氏台球的相关结果。

Medians and means in Finsler geometry

We investigate existence and uniqueness of p-means and the median of a probability measure on a Finsler manifold, in relation with the convexity of the support of the measure. We prove that the p-mean is the limit point of a continuous time gradient flow. Under some additional condition which is always satisfied for larger than or equal to 2, a discretization of this path converges to the p-mean. This provides an algorithm for determining those Finsler center points.

Convex bodies in Euclidean and Weil-Petersson geometries

On a convex body in a Euclidean space, we introduce a new variational formulation for its Funk metric, a Finsler metric compatible with the tautological Finsler structure of the convex body. We generalize the metric on Teichmuller spaces with the Weil-Petersson distance function. A set of similarities the resulting metric structure shares with Thurston's asymmetric metric is noted.

Sub-Finsler structures from the time-optimal control viewpoint for some nilpotent distributions

In this paper we study the sub-Finsler geometry as a time-optimal control problem. In particular, we consider non-smooth and non-strictly convex sub-Finsler structures associated with the Heisenberg, Grushin, and Martinet distributions. Motivated by problems in geometric group theory, we characterize extremal curves, discuss their optimality, and calculate the metric spheres, proving their Euclidean rectifiability.

广义Berwald射影Weyl度量

Generalized Berwald Projective Weyl metrics

本文在芬斯勒几何中提出广义Berwald射影Weyl度量，证明其C-射影不变性、所属GDW度量类的相关性质，拓展了Numata定理。

$\eta$-一致凸性与可除域

$β$-Uniform Convexity and Divisible Domains

本文证明严格凸可除域上的自然芬斯勒度量具有$\eta$-一致凸性，常数$\eta$与边界正则性相关，并借助AI辅助证明希尔伯特度量在适当假设下也满足该性质。

Needle decompositions and isoperimetric inequalities in Finsler geometry

Klartag recently gave a beautiful alternative proof of the isoperimetric inequalities of Levy-Gromov, Bakry-Ledoux, Bayle and E. Milman on weighted Riemannian manifolds. Klartag's approach is based on a generalization of the localization method (so-called needle decompositions) in convex geometry, inspired also by optimal transport theory. Cavalletti and Mondino subsequently generalized the localization method, in a different way more directly along optimal transport theory, to essentially non-branching metric measure spaces satisfying the curvature-dimension condition. This class in particula…

Average methods and their applications in Differential Geometry I

In Minkowski geometry the metric features are based on a compact convex body containing the origin in its interior. This body works as a unit ball with its boundary formed by the unit vectors. Using one-homogeneous extension we have a so-called Minkowski functional to measure the lenght of vectors. The half of its square is called the energy function. Under some regularity conditions we can introduce an average Euclidean inner product by integrating the Hessian matrix of the energy function on the Minkowskian unit sphere. Changing the origin in the interior of the body we have a collection of …

The Binet-Legendre Metric in Finsler Geometry

For every Finsler metric $F$ we associate a Riemannian metric $g_F$ (called the Binet-Legendre metric). The transformation $F \mapsto g_F$ is $C^0$-stable and has good smoothness properties, in contrast to previous constructions. The Riemannian metric $g_F$ also behaves nicely under conformal or bilipshitz deformation of the Finsler metric $F$. These properties makes it a powerful tool in Finsler geometry and we illustrate that by solving a number of named Finslerian geometric problems. We also generalize and give new and shorter proofs of a number of known results. In particular we answer a q…

The quotient girth of normed spaces, and an extension of Schäffer's dual girth conjecture to Grassmannians

In this note we introduce a natural Finsler structure on convex surfaces, referred to as the projective Finsler structure, which is dual in a sense to the obvious inclusion of a convex surface in a normed space. It has an associated projective girth, which is similar to the notion of girth defined by Schäffer. We prove the analogs of Schäffer's dual girth conjecture (proved by Álvarez-Paiva) and the Holmes-Thompson dual volumes theorem in the projective setting. We then show that the projective Finsler structure admits a natural extension to higher Grassmannians, and prove the corresponding th…

Finsler geometry and actions of the p-Schatten unitary groups

Let $p$ be an even positive integer and $U_p(H)$ be the Banach-Lie group of unitary operators $u$ which verify that $u-1$ belongs to the $p$-Schatten ideal $B_p(H)$. Let ${\cal O}$ be a smooth manifold on which $U_p(H)$ acts transitively and smoothly. Then one can endow ${\cal O}$ with a natural Finsler metric in terms of the $p$-Schatten norm and the action of $U_p(H)$. Our main result establishes that for any pair of given initial conditions $$ x\in {\cal O}\hbox{and} X\in (T{\cal O})_x $$ there exists a curve $δ(t)=e^{tz}\cdot x$ in ${\cal O}$, with $z$ a skew-hermitian element in the $p$-S…

Laplacian and spectral gap in regular Hilbert geometries

We study the spectrum of the Finsler--Laplace operator for regular Hilbert geometries, defined by convex sets with $C^2$ boundaries. We show that for an $n$-dimensional geometry, the spectral gap is bounded above by $(n-1)^2/4$, which we prove to be the infimum of the essential spectrum. We also construct examples of convex sets with arbitrarily small eigenvalues.

Displacement convexity of generalized relative entropies

We investigate the $m$-relative entropy, which stems from the Bregman divergence, on weighted Riemannian and Finsler manifolds. We prove that the displacement $K$-convexity of the $m$-relative entropy is equivalent to the combination of the nonnegativity of the weighted Ricci curvature and the $K$-convexity of the weight function. We use this to show appropriate variants of the Talagrand, HWI and the logarithmic Sobolev inequalities, as well as the concentration of measures. We also prove that the gradient flow of the $m$-relative entropy produces a solution to the porous medium equation or th…

Parameter invariant Lagrangian formulation of Kawaguchi geometry

This Ph.D. thesis is devoted to the constructions of Lagrangian formulation on Finsler and Kawaguchi manifolds. While Finsler geometry is a natural extension of Riemannian geometry, Kawaguchi geometry is the extension of Finsler geometry to higher order derivatives and to k-dimensional parameter space. The latter extension is also called areal geometry in some references. On Finsler (Kawaguchi) manifold, we can define a reparameterisation invariant 1 (k)-dimensional area by the Hilbert (Kawaguchi) form, which we take as an action. The equation of motion obtained from such action also has the p…