Quintessential difficulties

An alternative to a cosmological constant is quintessence, defined as a slowly-varying scalar field potential V(φ). If quintessence is observationally significant, an epoch of inflation is beginning at the present epoch, with φ the slowly-rolling inflaton field. In contrast with ordinary inflation, quintessence seems to require extreme fine tuning of the potential V(φ). The degree of fine-tuning is quantified in various cases.