The Robustness of Quintessence

Abstract

Recent observations seem to suggest that our Universe is accelerating implying that it is dominated by a fluid whose equation of state is negative. Quintessence is a possible explanation. In particular, the concept of tracking solutions permits to adress the fine-tuning and coincidence problems. We study this proposal in the simplest case of an inverse power potential and investigate its robustness to corrections. We show that quintessence is not affected by the one-loop quantum corrections. In the supersymmetric case where the quintessential potential is motivated by non-perturbative effects in gauge theories, we consider the curvature effects and the Kähler corrections. We find that the curvature effects are negligible while the Kähler corrections modify the early evolution of the quintessence field. Finally we study the supergravity corrections and show that they must be taken into account as $Q\approx m_{\rm Pl}$ at small red-shifts. We discuss simple supergravity models exhibiting the quintessential behaviour. In particular, we propose a model where the scalar potential is given by $V(Q)=\frac{Λ^{4+α}}{Q^α}e^{\fracκ{2}Q^2}$. We argue that the fine-tuning problem can be overcome if $α\ge 11$. This model leads to $ω_Q\approx -0.82$ for $Ω_{\rm m}\approx 0.3$ which is in good agreement with the presently available data.