Classical and Quantum Consistency of the DGP Model

TL;DR

This paper analyzes the classical and quantum consistency of the DGP model using the boundary effective action, confirming stability in most cases, identifying ghost issues in some cosmological solutions, and discussing quantum corrections and predictivity limits.

Contribution

It provides a comprehensive analysis of the DGP model's stability, quantum corrections, and proposes a specific counterterm choice to maintain predictivity and consistency.

Findings

The model is stable and ghost-free for most configurations.

Self-accelerating solutions exhibit ghost instabilities.

Quantum effects become significant below 1000 km, affecting predictivity.

Abstract

We study the Dvali-Gabadadze-Porrati model by the method of the boundary effective action. The truncation of this action to the bending mode \pi consistently describes physics in a wide range of regimes both at the classical and at the quantum level. The Vainshtein effect, which restores agreement with precise tests of general relativity, follows straightforwardly. We give a simple and general proof of stability, i.e. absence of ghosts in the fluctuations, valid for most of the relevant cases, like for instance the spherical source in asymptotically flat space. However we confirm that around certain interesting self-accelerating cosmological solutions there is a ghost. We consider the issue of quantum corrections. Around flat space \pi becomes strongly coupled below a macroscopic length of 1000 km, thus impairing the predictivity of the model. Indeed the tower of higher dimensional operators which is expected by a generic UV completion of the model limits predictivity at even larger length scales. We outline a non-generic but consistent choice of counterterms for which this disaster does not happen and for which the model remains calculable and successful in all the astrophysical situations of interest. By this choice, the extrinsic curvature K_{\mu\nu} acts roughly like a dilaton field controlling the strength of the interaction and the cut-off scale at each space-time point. At the surface of Earth the cutoff is \sim 1 cm but it is unlikely that the associated quantum effects be observable in table top experiments.