Abstract
Let M be a locally rotationally symmetric spacetime, and \(\xi ^a\) a conformal Killing vector for the metric on M, lying in the subspace spanned by the unit timelike direction and the preferred spatial direction, and with non-constant components. Under the assumption that the divergence of \(\xi ^a\) has no critical point in M, we obtain the necessary and sufficient condition for \(\xi ^a\) to generate a conformal Killing horizon. It is shown that \(\xi ^a\) generates a conformal Killing horizon if and only if either of the components (which coincide on the horizon) is constant along its orbits. That is, a conformal Killing horizon can be realized as the set of critical points of the variation of the component(s) of the conformal Killing vector along its orbits. Using this result, a simple mechanism is provided by which to determine if an arbitrary vector in an expanding LRS spacetime is a conformal Killing vector that generates a conformal Killing horizon. In specializing the case for which \(\xi ^a\) is a special conformal Killing vector, provided that the gradient of the divergence of \(\xi ^a\) is non-null, it is shown that LRS spacetimes cannot admit a special conformal Killing vector field, thereby ruling out conformal Killing horizons generated by such vector fields.
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Acknowledgements
The author gratefully acknowledges Miok Park of the IBS Center for Theoretical Physics of the Universe, for useful discussions during the early stages of this work. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of education (grant numbers) (NRF-2022R1I1A1A01053784) and (NRF-2021R1A2C1005748).
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Sherif, A.M. On the existence of conformal Killing horizons in LRS spacetimes. Gen Relativ Gravit 56, 15 (2024). https://doi.org/10.1007/s10714-024-03197-w
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DOI: https://doi.org/10.1007/s10714-024-03197-w