The harmonic oscillator as a distinguished dynamical system can be defined not only on the Euclidean plane but also on the sphere and on the hyperbolic plane, and more generally on any configuration space with constant curvature and with a metric of any signature, either Riemannian (definite positive) or Lorentzian (indefinite). In this paper we study the main properties of these `curved' harmonic oscillators simultaneously on any such configuration space, using a Cayley-Klein (CK) type approach, with two free parameters $\ki, \kii$ which altogether correspond to the possible values for curvature and signature type: the generic Riemannian and Lorentzian spaces of constant curvature (sphere ${\bf S}^2$, hyperbolic plane ${\bf H}^2$, AntiDeSitter sphere ${\bf AdS}^{\unomasuno}$ and DeSitter sphere ${\bf dS}^{\unomasuno}$) appear in this family, with the Euclidean and Minkowski spaces as flat limits.
We solve the equations of motion for the `curved' harmonic oscillator and obtain explicit expressions for the orbits by using three different methods: first by direct integration, second by obtaining the general CK version of the Binet's equation and third, as a consequence of its superintegrable character. The orbits are conics with centre at the potential origin in any CK space, thereby extending this well known Euclidean property to any constant curvature configuration space. The final part of the article, that has a more geometric character, presents those results of the theory of conics on spaces of constant curvature which are pertinent.
Gromov, Cauchy and causal boundaries for Riemannian, Finslerian and Lorentzian manifolds
最近，时空V的因果边界的旧概念以一种一致的方式被重新定义。对标准共形定常时空V = R x M的这个边界$\partial V$的计算表明，一个自然的紧化$M_B$与M上的任何黎曼度量有关，或者更一般地说，与任何芬斯勒度量有关。相应的边界$\partial_B M$构造的Busemann型函数。粗略地说，$\partial_B M$表示M中所有方向的集合，包括渐近和“有限”（或“不完全”）方向。这个Busemann边界$\partial_B M$与两个经典边界有关：Cauchy边界和Gromov边界。我们的目标是：（1）研究两者的微妙之处，任何广义（可能非对称）距离的柯西边界和任何（可能不完全）芬斯勒流形的格罗莫夫紧化，（2）引入新的布斯曼紧化$M_B$，将其与前两个完备化联系起来，（3）给出任何标准共形稳态时空的因果边界$\partial V$的完整描述。
On the Stress-Energy Tensor of Quantum Fields in Curved Spacetimes - Comparison of Different Regularization Schemes and Symmetry of the Hadamard/Seeley-DeWitt Coefficients
