In a previous paper we classified complete stationary surfaces (i.e. spacelike surfaces with zero mean curvature) in 4-dimensional Lorentz space R 4 1 which are algebraic and with total Gaussian curvature − KdM = 4π. Here we go on with the study of such surfaces with − KdM = 6π. It is shown in this paper that the topological type of such a surface must be a Möbius strip. On the other hand, new examples with a single good singular end are shown to exist.By Gauss-Bonnet type formulas established in [2], we know that complete algebraic stationary surfaces with − KdM = 6π must be non-orientable. On the other hand, we obtained a lower bound in [5] for any g ≥ 0 as below:(1)Thus it is natural to study complete, algebraic, non-orientable stationary surfaces with total curvature 6π, which is the least possible value. By (1) and the generalized Jorge-Meeks formula (see Theorem 2.7), we know such surface M must be homomorphic to a projective plane with one or two ends.
Meeks have obtainedKnown results in R 3 [6]: There is a unique complete, immersed minimal surface with total curvature − KdM = 6π, which is now called Meeks' Möbius strip. In particular, the topological type of a projective plane with two punctures does not occur.New examples appear in R 4 1 . We have constructed complete stationary Möbius strips with total curvature 6π in [5]. Among them, one family is a generalization of Meeks and Olivaira's examples; another family has an essential singularity at the end. We will review the descriptions of them in Section 3.Besides that, we are still interested to know other possible examples in R 4 1 . Can the topological type of a projective plane with two punctures be realized as a stationary surface in R 4 1 ? On the other hand, besides Meeks' example and its deformations as mentioned above, does there exist new type of stationary Möbius strips? These two questions are answered at here.
Conclusion 1:There exists a family of complete, immersed stationary Möbius strips in R 4 1 with a good singular end and total curvature − M KdM = 6π.Recall that an end is called singular end if the two Gauss maps satisfy φ =ψ. Please see Definition 2.4 in Section 2, or [2] for detailed explanation. This is a special phenomenon which never occur for minimal surfaces in R 3 . In particular, the total curvature integral converges around such an end if, and only if, these two functions take the same value with different multiplicities. This case we call it a good singular end.Conclusion 2: There does not exist examples with − KdM = 6π and homomorphic to the projective plane punctured at two points.A noteworthy observation (Lemma 4.1) is that the flux at any end of a stationary Möbius strip (with several punctures) must vanish. It is interesting to know whether this is true for any other non-orientable stationary surface. This paper is organized as follows. In Section 2 we review the Weierstrass representation and Gauss-Bonnet type formulas. The examples with a good singular end are shown to exist in Section 3, together with a discussion of...