Homologically visible closed geodesics on complete surfaces

In this paper, we give multiple situations when having one or two geometrically distinct closed geodesics on a complete Riemannian cylinder, a complete Möbius band or a complete Riemannian plane leads to having infinitely many geometrically distinct closed geodesics. In particular, we prove that any complete cylinder with isolated closed geodesics has zero, one or infinitely many homologically visible closed geodesics; this answers a question of Alberto Abbondandolo.

Weingarten Type Surfaces in ℍ2 × ℝ and 𝕊2 × ℝ

In this article, we study complete surfaces Σ, isometrically immersed in the product spaces ℍ2 × ℝ or 𝕊2 × ℝ having positive extrinsic curvature Ke . Let Ki denote the intrinsic curvature of Σ. Assume that the equation aKi + bKe = c holds for some real constants a ≠ 0,b >0, and c. The main result of this article states that when such a surface is a topological sphere, it is rotational.

Some properties of Grauert type surfaces

In a previous work, we classified weakly complete surfaces which admit a real analytic plurisubharmonic exhaustion function; we showed that, if they are not proper over a Stein space, then they admit a pluriharmonic function, with compact Levi-flat level sets foliated with dense complex leaves. We called these Grauert type surfaces. In this note, we investigate some properties of these surfaces. Namely, we prove that the only compact curves that can be contained in them are negative in the sense of Grauert and that the level sets of the pluriharmonic function are connected, thus completing the analogy with the Cartan–Remmert reduction of a holomorphically convex space. Moreover, in our classification theorem, we had to pass to a double cover to produce the pluriharmonic function; the last part of the present paper is devoted to the construction of an example where passing to a double cover cannot be avoided.