Invariant Measures of Horospherical Flows on Noncompact Homogeneous Spaces.
Let be a -space such that the orbit space is metrizable. Suppose a family of slices is given at each point of . We study a construction which associates, under some conditions on the family of slices, with any metric on an invariant metric on . We show also that a family of slices with the required properties exists for any action of a countable group on a locally compact and locally connected metric space.
On donne une construction géométrique d’invariants généralisant la classe de Maslov-Arnold d’une immersion lagrangienne dans un fibré cotangent et l’indice de Maslov-Arnold-Leray d’une immersion lagrangienne -orientée dans : la classe de Maslov-Arnold universelle d’un fibré symplectique et l’indice de Maslov-Arnold-Leray d’un fibré -symplectique, c’est-à-dire dont le groupe structural est le revêtement à feuillets de . Tout ceci relève d’une situation géométrique générale dans laquelle s’introduisent...
We study numerical and polynomial invariants of piecewise-linear knots, with the goal of better understanding the space of all knots and links. For knots with small numbers of edges we are able to find limits on polynomial or Vassiliev invariants sufficient to determine an exact list of realizable knots. We thus obtain the minimal edge number for all knots with six or fewer crossings. For example, the only knot requiring exactly seven edges is the figure-8 knot.
We definite invariants of translation surfaces which refine Veech groups. These aid in exact determination of Veech groups. We give examples where two surfaces of isomorphic Veech group cannot even share a common tree of balanced affine coverings. We also show that there exist translation surfaces of isomorphic Veech groups which cannot affinely cover any common surface. We also extend a result of Gutkin and Judge and thereby give the first examples of noncompact Fuchsian...