Conformal isometry of the lukewarm Reissner-Nordström-de Sitter spacetime

Abstract: It is known that the extremal Reissner-Nordstr\"om black hole possesses a discrete conformal isometry that exchanges the black hole horizon with infinity. It is also known that the Reissner-Nordstr\"om-de Sitter spacetime posseses a similar discrete conformal isometry which exchanges the event horizon of the black hole with the cosmological horizon. In this short paper we will continue this line of thought and extend the conformal isometry of the latter spacetime and give an unphysical interpretation of the negative root.