Does SO(2,2) symmetry lead to an additional U(1) symmetry in 5-dimensional Einstein-scalar theories?

Abstract

Solving Einstein equations including the matter fields in dimensions higher than four is computationally challenging. However, the existence of symmetries facilitates these calculations. Among these symmetries, we can mention the SO(2,2) symmetry that arises in the near-horizon geometries of extremal black holes with vanishing horizon area in four dimensions \cite{EVH/CFT} and higher dimensions \cite{Sadeghian:2015}. Solutions of Einstein theories including scalar and Maxwell fields with SO(2,2) symmetry have been classified in four, five, and higher dimensions \cite{Sadeghian:2014}. For the Einstein-Maxwell-Lambda theory, a theorem states that SO(2,2) symmetry leads to an additional U(1) symmetry and therefore unique axisymmetric solutions. Nevertheless, in the presence of a scalar field, this symmetry group is not large enough in five dimensions to guarantee solution uniqueness, and the additional U(1) symmetry remains a conjecture in \cite{Sadeghian:2014}. Here, we study the Einstein equations of theories with a five-dimensional scalar field using the Lie symmetry method for solving partial differential equations. We challenge the conjecture in \cite{Sadeghian:2014} and find a solution that depends on both $θ$ and $ψ$ coordinates as a counterexample to that conjecture.