The short ruler on the torus

ABSTRACT

We can shorten any path that links two given points by applying short ruler transforms iteratively. In this article we take a closer look at a short ruler process on the torus. The torus is a compact Riemannian manifold and at least a subsequence of the process converges to a geodesic between the two points. However, on compact Riemann manifolds there might exist different limit geodesics (with the same length). On the torus, the geodesics with the same length are isolated and the limit geodesic is unique.     

Geodesic knots in closed hyperbolic 3-manifolds

We consider the existence of simple closed geodesics or “geodesic knots” in finite volume orientable hyperbolic 3-manifolds. Every such manifold contains at least one geodesic knot by results of Adams, Hass and Scott in (Adams et al. Bull. London Math. Soc. 31: 81–86, 1999). In (Kuhlmann Algebr. Geom. Topol. 6: 2151–2162, 2006) we showed that every cusped orientable hyperbolic 3-manifold in fact contains infinitely many geodesic knots. In this paper we consider the closed manifold case, and show that if a closed orientable hyperbolic 3-manifold satisfies certain geometric and arithmetic conditions, then it contains infinitely many geodesic knots. The conditions on the manifold can be checked computationally, and have been verified for many manifolds in the Hodgson-Weeks census of closed hyperbolic 3-manifolds. Our proof is constructive, and the infinite family of geodesic knots spiral around a short simple closed geodesic in the manifold.      

A New Proof of the Existence of Embedded Surfaces with Anosov Geodesic Flow

We give a new proof of the existence of compact surfaces embedded in ?³ with Anosov geodesic flows. This proof starts with a noncompact model surface whose geodesic flow is shown to be Anosov using a uniformly strictly invariant cone condition. Using a sequence of explicit maps based on the standard torus embedding, we produce compact embedded surfaces that can be seen as small perturbations of the Anosov model system and hence are themselves Anosov.     

On a New Class of Vector Variational Control Problems

Abstract

In this paper, we introduce geodesic (strongly) b-V-KT-pseudoinvex multidimensional control problems. This new class of multiobjective variational control problems, involving multiple integral cost functionals, is described such that every geodesic Kuhn–Tucker point is geodesic efficient solution. In addition, to illustrate the effectiveness of our main result, the paper is completed with an application.     

On the Mean Absolute Geodesic Curvature of Closed Curves in 2-Dimensional Space Forms

In this paper,we establish some formulas on closed curves in 2-dimensional space forms.Mean absolute geodesic curvature is introduced to describe the average curving of a closed curve.Inthis sense,a closed curve could be compared with a geodesic circle that is the boundary of a convex geodesic circular disk containing the closed curve.The comparison can be used to show some properties of space forms only on themselves.     

(1+1)-Correlators and moving massive defects

We study correlation functions of scalar operators on the boundary of the AdS₃ space deformed by moving massive particles in the context of the AdS/CFT duality. To calculate two-point correlation functions, we use the geodesic approximation and the renormalized image method, obtained from the traditional image method with the renormalization taken into account. We compare results obtained using the renormalized image method with direct calculations using tracing of winding geodesics around the cone singularities. Examples demonstrate that the results coincide. We show that correlators in the geodesic approximation have a zone structure, which depends substantially on the particle mass and velocity.     

On the asymptotic behavior of expanding gradient Ricci solitons

Let (M, g, f) be an n-dimensional expanding gradient Ricci soliton with faster-than-quadratic-decay curvature, i.e., ${\lim_{{\rm dist}(O,x)\rightarrow\infty} |{\rm Sect}(x)|\cdot {\rm dist}(O,x)^2=0}$ . When M is simply connected at infinity and n??? 3, we show that its tangent cone at infinity must be a manifold and is isometric to ${\mathbb{R}^n}$ . Here, we also assume that M has only one end for the simplicity of the statement. A crucial step to gain the regularity of the tangent cone at infinity is to prove that the injectivity radius grows linearly. This can be achieved by combining the curvature assumption and a lower bound estimate of volume ratio of all geodesic balls, which is attained as Theorem 3. On the other hand, we also study the asymptotic volume ratio of non-steady gradient Ricci solitons under other weaker conditions.     

FORMULE DE TRACE SEMI-CLASSIQUE SUR UNE VARIETE DE DIMENSION 3 AVEC UN POTENTIEL DE DIRAC

ABSTRACT

On a riemannian manifold of dimension 3, it is possible to change the laplacian Δ at a single point p. This procedure gives the so-called Dirac potential, and we study the associated wave equation. We first show that the propagator can be written as a sum in which each operator takes into account n diffractions at p. We then show that the curve obtained by following, one after another, n geodesic segments emanating from, and returning to p, gives a singularity in the trace formula. The principal part of this singularity is also computed.     

Non-harmonic Cones are Heisenberg Uniqueness Pairs for the Fourier Transform on $${\mathbb {R}}^n$$

In this article, we prove that a cone is a Heisenberg uniqueness pair corresponding to sphere as long as the cone does not completely recline on the level surface of any homogeneous harmonic polynomial on \({\mathbb {R}}^n\). We derive that \(\left( S^2, \text { paraboloid}\right) \) and \(\left( S^2, \text { geodesic of } S_r(o)\right) \) are Heisenberg uniqueness pairs for a class of certain symmetric finite Borel measures in \({\mathbb {R}}^3\). Further, we correlate the problem of Heisenberg uniqueness pairs to the sets of injectivity for the spherical mean operator.     

Limiting angle of Brownian motion on certain manifolds

Summary. Suppose that M is a complete, simply connected Riemannian manifold of non-positive sectional curvature with dimension m ≧ 3. If, outside a fixed compact set, the sectional curvatures are bounded above by a negative constant multiple of the inverse of the square of the geodesic distance from a fixed point and below by another negative constant multiple of the square of the geodesic distance, then the angular part of Brownian motion on M tends to a limit as time tends to infinity, and the closure of the support of the distribution of this limit is the entire S ^m−1 . This improves a result of Hsu and March. Received: 7 December 1994/In revised form: 2 September 1995     

The Relation of the Morse Index of Closed Geodesics with the Maslov-type Index of Symplectic Paths

In this paper, we consider the relation of the Morse index of a closed geodesic with the Maslov–type index of a path in a symplectic group. More precisely, for a closed geodesic c on a Riemannian manifold M with its linear Poincaré map P (a symplectic matrix), we construct a symplectic path γ(t) starting from identity I and ending at P, such that the Morse index of the closed geodesic c equals the Maslov–type index of γ. As an application of this result, we study the parity of the Morse index of any closed geodesic. Project 10071040 supported by NNSF, 200014 supported by Excellent. Ph.D. Funds of ME of China, and PMC Key Lab. of ME of China     

Examples of invariant semi-Riemannian metrics on 4-dimensional lie groups

We consider a family of left invariant semi- Riemannian metrics on some extension of the Heisenberg group by the real line (denoted by ). We find a 3-dimensional foliation, which is minimal but not totally geodesic with respect to all the metrics of this family. Other two 3-dimensional totally geodesic (isometric) foliations on are determined. We consider also a non-holonomic 3-dimensional distribution, admitting integral surfaces which are totally geodesic in the ambiant space . Two of them are isomorphic with the two-dimensional non-commutative Lie group (which is not totally geodesic in the additive Lie groupR ⁴!). Following the different possible choices of the signatures of the metrics and the sign of the parameters, we put in evidence twelve new classes of invariant spacetime structures onR ⁴, together with their energy-momenta.     

Contribution of periodic diffractive geodesics

On an euclidean surface with conical singularities, the wave-trace is expected to be singular at L where L is the length of some diffractive periodic geodesic. In this paper, we compute the leading term of the singularity brought to the trace by a regular, isolated diffractive geodesic and by a regular family of periodic non-diffractive geodesic. These results can be applied to polygons.     

Geometry of the nets in equiaffine spaces

The derivation formulae of the vector fields of an arbitrary net belonging to the n-dimensional equiaffine spaceEqA _n are introduced and the conditions which satisty their coefficients are found. The following special nets: Chebyshev of the first and second kind, strongly parallel of the first kind, geodesic, generalized metrical Chebyshev and symmetric nets are studied. Their characteristics by the coefficients of the derivation equations are obtained. Chebyshev and geodesic curvatures of the lines of the net belonging toEqA _n and Chebyshev and geodesic vectors of the nets are introduced. Equiaffine spaces containing above mention special nets are defined.The present investigation is partially supported by the Nacional Science Fund of the Ministry of Science and Education, Republic of Bulgaria under grant MM 64.     

Methoden der Differentialgeometrie in Himmelsmechanik und Astronomie

With methods of differential geometry we can find three laws of Kepler type for the restricted 3-body problem. The first law is a geodesic equation, the third law is comparable with the formula of Gauß-Bonnet. Applications to astronomy are mentioned. For proofs and applications see [1].     

Optical Tomography on Simple Riemannian Surfaces

ABSTRACT

Optical tomography means the use of near-infrared light to determine the optical absorption and scattering properties of a medium. In the stationary Euclidean case the dynamics are modeled by the radiative transport equation, which assumes that, in the absence of interaction, particles follow straight lines. Here we shall study the problem in the presence of a Riemannian metric where particles follow the geodesic flow of the metric. In particular, we study the problem in dimension two, where the analysis is more delicate than in the higher dimensional cases.     

Hyperbolic Volume of Manifolds with Geodesic Boundary and Orthospectra

In this paper we describe a function F _n : R ₊ → R ₊ such that for any hyperbolic n-manifold M with totally geodesic boundary ${\partial M \neq \emptyset}In this paper we describe a function F _n : R ₊ → R ₊ such that for any hyperbolic n-manifold M with totally geodesic boundary ?M 1 ?{\partial M \neq \emptyset} , the volume of M is equal to the sum of the values of F _n on the orthospectrum of M. We derive an integral formula for F _n in terms of elementary functions. We use this to give a lower bound for the volume of a hyperbolic n-manifold with totally geodesic boundary in terms of the area of the boundary.     

Exact Location of the Weighted Fermat–Torricelli Point on Flat Surfaces of Revolution

We find the exact location of the weighted Fermat–Torricelli point of a geodesic triangle on flat surfaces of revolution (circular cylinder and circular cone) in the three dimensional Euclidean space by applying a cosine law of three circular helixes which form a geodesic triangle on a circular cylinder, an explicit solution of the corresponding weighted Fermat–Torricelli point in the dimensional Euclidean space by calculating some lengths of geodesic arcs and angles and by using some lengths of straight lines on a circular cone which connect the vertices of the geodesic triangle with the vertex of the circular cone.     

Locally symmetric minimal affine Lagrangian surfaces in C<Superscript>2</Superscript>

One of the basic facts known in the theory of minimal Lagrangian surfaces is that a minimal Lagrangian surface of constant curvature in C ² must be totally geodesic. In affine geometry the constancy of curvature corresponds to the local symmetry of a connection. In Opozda (Geom. Dedic. 121:155–166, 2006), we proposed an affine version of the theory of minimal Lagrangian submanifolds. In this paper we give a local classification of locally symmetric minimal affine Lagrangian surfaces in C ². Only very few of surfaces obtained in the classification theorems are Lagrangian in the sense of metric (pseudo-Riemannian) geometry. The research supported by the KBN grant 1 PO3A 034 26.