Robustness of quintessence - art. no. 103502

Recent observations seem to suggest that our Universe is accelerating, impl ying that it is dominated by a fluid whose equation of state is negative. Q uintessence is a possible explanation. In particular, the concept of tracki ng solutions permits us to address 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 i s not affected by the one-loop quantum corrections. In the supersymmetric c ase where the quintessential potential is motivated by nonperturbative effe cts in gauge theories, we consider the curvature effects and the Kahler cor rections. We find that the curvature effects are negligible while the Kahle r corrections modify the early evolution of the quintessence field. Finally we study the supergravity corrections and show that they must be taken int o account as Q approximate to m(Pl) at small redshifts. We discuss simple s upergravity models exhibiting the quintessential behavior. In particular, w e propose a model where the scalar potential is given by V(Q) = (Lambda(4+a lpha)/Q(alpha))e((kappa/2)Q2). We argue that the fine-tuning problem can be overcome if alpha greater than or equal to 11. This model leads to omega(Q ) approximate to -0.82 for Omega(m) approximate to 0.3 which is in good agr eement with the presently available data.