Towards the core of the cosmological constant problem

Abstract

We apply a new self-tuning mechanism to the well-known Kachru-Kallosh-Linde-Trivedi (KKLT) model to address the cosmological constant problem. In this mechanism, the cosmological constant λ contains a supersymmetry breaking term ESB besides the usual scalar potential Vscalar of the N = 1 supergravity, which is distinguished from the usual theories where λ is directly identified with Vscalar alone. Also in this mechanism, whether λ vanishes or not is basically determined by the tensor structure of the scalar potential density, not by the zero or nonzero values of the scalar potential itself. As a result of this application, we find that the natural scenario for the vanishing λ of the present universe is to take one of the anti-de Sitter (AdS) (rather than de Sitter (dS)) vacua of KKLT as the background vacuum of our present universe. This AdS vacuum scenario has nicer properties as compared with dS vacua of the usual flux compactifications. The background vacuum is stable both classically and quantum mechanically (no tunneling instabilities), and the value λ = 0 is also stable against quantum corrections because in this scenario the perturbative corrections of Vscalar and quantum fluctuations dQ δÎbrane(NS) + dδÎbrane(R) on the branes are all gauged away by an automatic cancellation between Vscalar + dδÎbrane(NS) + dδÎbrane(R) (R) and ESB.