On Rectification of Circles and an Extension of Beltrami's Theorem

Rectification of circles and quaternions

Consider a bundle of circles passing through 0 in 4-dimensional space. It is said to be rectifiable if there is a germ of diffeomorphism at 0 that takes all circles from our bundle to straight lines. We will give a classification of all rectifiable bundles of circles containing sufficiently many circles in general position. This result is surprisingly different from those in dimensions 2 and 3(Khovanskii and Izadi) due to a connection with the quaternionic algebra.

Some Modifications of the Theorem of Beltrami

The two main topics of this text are as follows: Firstly, three modifications of the theorem of Beltrami will be presented for diffeomorphisms between Riemannian manifolds and a space form which preserve the geodesic circles, the geodesic hyperspheres, or the minimal surfaces, respectively. Secondly, it is defined what it means for an infinitesimal deformation of a metric to preserve the geodesics up to first order, and a corresponding infinitesimal version of Beltrami's theorem is given.

Weil-Petersson圆周同胚的调和延拓

Harmonic extension of Weil-Petersson circle homeomorphisms

从调和映射角度研究Weil-Petersson圆周同胚，证明其等价于到双曲盘的拟共形调和延拓具有平方可积Beltrami微分，并引入反全纯L²能量。