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Asymptotic behavior for singularities of the mean curvature flow. (English) Zbl 0694.53005
This paper deals with the motion of a surface by its mean curvature vector. The context here is a one parameter family $$F_ 1=F(,t)$$ with each $$F_ 1$$ a smooth immersion into $$R^{n+1}$$ of the fixed n- dimensional manifold M. Motion by the mean curvature vector is described by the differential equation $\frac{d}{dt}F(p,t)=H(p,t),$ where H(p,t) is the mean curvature vector of the hypersurface $$M_ i=F_ i(M)$$ at F(p,t). Typically, initial data $$F(p,0)=F_ 0(p)$$ is also imposed. In this paper, $$M=M_ 0$$ is assumed to be a compact manifold without boundary, and it is assumed that $$M_ 0$$ bounds a non-convex region. In a previous paper, the author considered the situation when $$M_ 0$$ is assumed to bound a convex region, and regularity results were obtained. In the non-convex case considered here singularities are expected to develop and the behavior of the surfaces as they approach such singularities is investigated.
The main result is that if a singularity develops at time T, and if a bound of the form $$\max \{| A|^ 2/M_ i\}\leq const/(T-t)$$ holds, where A is the second fundamental form, then there is a rescaled sequence near the singularity which converges to a limiting hypersurface and such limiting hypersurfaces satisfy the equation $$H=<x,\nu >$$, where x is the position vector, H is the mean curvature, and $$\nu$$ is the unit normal such that the mean curvature vector is given by $$H=-H\nu$$. Important for the proof is a general monotonicity formula obtained for surfaces moving along their curvature vector. It is shown by an example that the curvature bound above does, in fact, hold for a non-trivial family of surfaces.
Reviewer: H.Parks

##### MSC:
 53A07 Higher-dimensional and -codimensional surfaces in Euclidean and related $$n$$-spaces 53C40 Global submanifolds
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