Bulletin of the
Korean Mathematical Society BKMS

Let $P$ be a spacelike $(n-2)$-dimensional submanifold of an $n$-dimensional Lorentz manifold $M$ and let $\sigma$ be a $P$-normal null geodesic with $Ric(\sigma',\, \sigma') \geq m$, for any given nonpositive constant $m$. We establish a sufficient condition such that there is a focal point of $P$ along $\sigma$.

Keywords: Lorentz manifold, null geodesic, focal point, warped product

MSC numbers: 53C50