Physical Review Letters
We present evidence that the simplest particle-physics scalar-field models of dynamical dark energy can be separated into distinct behaviors based on the acceleration or deceleration of the field as it evolves down its potential towards a zero minimum. We show that these models occupy narrow regions in the phase plane of w and w′, the dark energy equation of state and its time derivative in units of the Hubble time. Restricting an energy scale of the dark energy microphysics limits how closely a scalar field can resemble a cosmological constant. These results, indicating a desired measurement resolution of order σ(w′)≈(1+w), define firm targets for observational tests of the physics of dark energy.
Caldwell, R. R. and Linder, Eric V., "Limits of Quintessence" (2005). Open Dartmouth: Faculty Open Access Articles. 2014.