We explore the implications of gravitationally lensed QSOs and high-redshift SNe Ia observations for spatially flat cosmological models in which a classically evolving scalar field currently dominates the energy density of the Universe. We consider two representative scalar field potentials that give rise to effective decaying $Lambda $ (``quintessence) models: pseudo-Nambu-Goldstone bosons ($V(phi)=M^4(1+cos (phi /f)) $) and an inverse power-law potential ($V(phi)=M^{4+alpha}phi ^{-alpha}$). We show that a large region of parameter space is consistent with current data if $Omega_{m0} > 0.15$. On the other hand, a higher lower bound for the matter density parameter suggested by large-scale galaxy flows, $Omega_{m0} > 0.3$, considerably reduces the allowed parameter space, forcing the scalar field behavior to approach that of a cosmological constant.
تحميل البحث