Conformal geometry on a class of embedded hypersurfaces in spacetimes
Abstract
In this work, we study various geometric properties of embedded spacelike hypersurfaces in 1 + 1 + 2 decomposed spacetimes with a preferred spatial direction, denoted e ^{ μ }, which are orthogonal to the fluid flow velocity of the spacetime and admit a proper conformal transformation. To ensure nonvanishing and positivity of the scalar curvature of the induced metric on the hypersurface, we impose that the scalar curvature of the conformal metric is nonnegative and that the associated conformal factor φ satisfies ${\hat{\varphi }}^{2}+2\hat{\hat{\varphi }} > 0$ , where $\hat{\ast }$ denotes derivative along the preferred spatial direction. Firstly, it is demonstrated that such hypersurface is either of Einstein type or the spatial twist vanishes on them, and that the scalar curvature of the induced metric is constant. It is then proved that if the hypersurface is compact and of Einstein type and admits a proper conformal transformation, then these hypersurfaces must be isomorphic to the threesphere, where we make use of some well known results on Riemannian manifolds admitting conformal transformations. If the hypersurface is not of Einstein type and have nowhere vanishing sheet expansion, we show that this conclusion fails. However, with the additional conditions that the scalar curvatures of the induced metric and the conformal metric coincide, the associated conformal factor is strictly negative and the third and higher order derivatives of the conformal factor vanish, the conclusion that the hypersurface is isomorphic to the threesphere follows. Furthermore, additional results are obtained under the conditions that the scalar curvature of a metric conformal to the induced metric is also constant. Finally, we consider some of our results in context of locally rotationally symmetric spacetimes and show that, if the hypersurfaces are compact and not of Einstein type, then under specified conditions the hypersurface is isomorphic to the threesphere, where we constructed explicit examples of proper conformal Killing vector fields along e ^{ μ }.
 Publication:

Classical and Quantum Gravity
 Pub Date:
 February 2022
 DOI:
 10.1088/13616382/ac45db
 arXiv:
 arXiv:2112.08753
 Bibcode:
 2022CQGra..39d5004S
 Keywords:

 conformal transformation;
 hypersurfaces;
 constant scalar curvature;
 LRS II spacetimes;
 Mathematics  Differential Geometry;
 General Relativity and Quantum Cosmology
 EPrint:
 21 pages, no figure, Accepted for publication in CQG