arXiv subjects
Publications and source records attributed to Bernd Stratmann.
We show that all symplectically aspherical fillings of the unit cotangent bundle of a given odd-dimensional sphere are diffeomorphic to the corresponding unit co-disc bundle. The concept of fittings previously introduced is not needed.
Extracting isolated rays from a symplectic manifold result in a manifold symplectomorphic to the initial one. The same holds for higher dimensional parametrized rays under an additional condition. More precisely, let $(M,ω)$ be a symplectic manifold. Let $[0,\infty)\times Q\subset\mathbb{R}\times Q$ be considered as parametrized rays $[0,\infty)$ and let $φ:[-1,\infty)\times Q\to M$ be an injective, proper, continuous map immersive on $(-1,\infty)\times Q$. If for the standard vector field $\frac{\partial}{\partial t}$ on $\mathbb{R}$ and any further vector field $ν$ tangent to $(-1,\infty)\times Q$ the equation $φ^*ω(\frac{\partial}{\partial t},ν)=0$ holds then $M$ and $M\setminus φ([0,\infty)\times Q)$ are symplectomorphic.
Let $M$ be a manifold with an exact symplectic form $ω$. Then there is a nowhere vanishing primitive $β$ for $ω$, i.e. $ω=\mathrm{d}β$.
For a proper Hamiltonian action of a Lie group $G$ on a Kähler manifold $(X,ω)$ with momentum map $μ$ we show that the symplectic reduction $μ^{-1}(0)/G$ is a normal complex space. Every point in $μ^{-1}(0)$ has a $G$-stable open neighborhood on which $ω$ and $μ$ are given by a $G$-invariant Kähler potential. This is used to show that $μ^{-1}(0)/G$ is a Kähler space. Furthermore we examine the existence of potentials away from $μ^{-1}(0)$ with both positive and negative results.
For a hyperbolic map f on a saddle type fractal Lambda with self-intersections, the number of f- preimages of a point x in Lambda may depend on x. This makes estimates of the stable dimensions more difficult than for diffeomorphisms or for maps which are constant-to-one. We employ the thermodynamic formalism in order to derive estimates for the stable Hausdorff dimension function delta^s on Lambda, in the case when f is conformal on local stable manifolds. These estimates are in terms of a continuous function on Lambda which bounds the preimage counting function from below. As a corollary we obtain that if delta^s attains its maximal possible value in Lambda, then the stable dimension is constant throughout Lambda, whereas the preimage counting function is constant on at least an open and dense subset of Lambda. In particular, this shows that if at some point in Lambda, the stable dimension is equal to the analogue of the similarity dimension in the stable direction at that point, then f behaves very much like a homeomorphism on Lambda. Finally we also obtain results about the stable upper box dimension for these type of fractals. We end the paper with a discussion of two explicit examples.