Warping with dilatation symmetry and self-tuning of the cosmological constant

Abstract: We investigate consequences of an ultraviolet fixed point in quantum gravity for the cosmological constant. For this purpose we perform dimensional reduction of a general dilatation symmetric effective action $\Gamma$ in dimension $d>4$ to an effective four-dimensional theory of gravity with a dilaton field. We find a stable flat phase in the space of extrema of $\Gamma$ which results in a vanishing four-dimensional cosmological constant $\Lambda$. In order to understand the self-tuning mechanism leading to $\Lambda = 0$ we discuss in detail the most general warped geometries with maximal four-dimensional symmetry and $SO(d-4)$ isometry of internal space. While the solutions of the $d$-dimensional field equations admit singular spaces with arbitrary $\Lambda$, the extremum condition for $\Gamma$ imposes additional restrictions which result in $\Lambda = 0$. In cosmology, the dilatation symmetric fixed point may only be reached for asymptotic time $t \to \infty$. At finite $t$ dilatation anomalies result in an effective potential and mass for the pseudo-dilaton or cosmon and in dark energy.