Nonminimal coupling, exponential potentials and the w<-1 regime of dark energy -: art. no. 087302

Recent observations and theoretical considerations have motivated the study of models for dark energy with equation of state characterized by a parameter w=p/rho<-1. Such models, however, are usually believed to be inviable due to their instabilities against classical perturbations or potentially catastrophic vacuum decays. In this Brief Report, we show that a simple quintessential model with potential V(phi)=Ae(-sigmaphi) and a gravitational coupling of the form (1+|xi|phi(2))R can exhibit, for large sets of initial conditions, asymptotic de Sitter behavior with w<-1 regimes. Nevertheless, the model is indeed stable at classical and quantum level.