## Turkish Journal of Mathematics

#### Article Title

### Normalized null hypersurfaces in non-flat Lorentzian space forms satisfying $L_r x =\mathcal U x +b$

#### DOI

10.3906/mat-2102-37

#### Abstract

In the present work, we classify normalized null hypersurfaces $x:(M,g,N)\to Q^{n+2}_1(c)$ immersed into one of the two real standard nonflat Lorentzian space-forms and satisfying the equation $L_r x=\mathcal U x+b$ for some field of screen constant matrices $\mathcal U$ and some field of screen constant vectors $b\in\mathbb{R}^{n+2}$, where $L_r$ is the linearized operator of the $(r+1)-$mean curvature of the normalized null hypersurface for $r=0,...,n$. We show that if the immersion $x$ is a solution of the equation $L_r x=\mathcal U x+b$ for $1\leq r\leq n$ and the normalization $N$ is quasi-conformal, then $M$ is either an $(r+1)-$maximal null hypersurface, or a totally umbilical (or geodesic) null hypersurface or an almost isoparametric normalized null hypersurface with at most two non-zero principal curvatures. We also show that a null hypersurface $M$, of a real standard semi-Riemannian nonflat space form $Q_t^{n+2}(c)$, admits a totally umbilical screen distribution (and then $M$ is totally umbilical or totally geodesic) if and only if $M$ is a section of $Q_t^{n+2}(c)$ by a hyperplane of $\mathbb{R}^{n+3}$. In particular a null hypersurface $M\to Q_t^{n+2}(c)$ is totally geodesic if and only if $M$ is a section of $Q_t^{n+2}(c)$ by a hyperplane of $\mathbb{R}^{n+3}$ passing through the origin.

#### Keywords

Normalized null hypersurface, screen quasi-conformal, second order differential operator, screen distribution, Higher order mean curvature

#### First Page

1809

#### Last Page

1834

#### Recommended Citation

TETSING, HANS FOTSING
(2021)
"Normalized null hypersurfaces in non-flat Lorentzian space forms satisfying $L_r x =\mathcal U x +b$,"
*Turkish Journal of Mathematics*: Vol. 45:
No.
4, Article 31.
https://doi.org/10.3906/mat-2102-37

Available at:
https://journals.tubitak.gov.tr/math/vol45/iss4/31