title: Limits of quintessence.
abstract: 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 sigma(w') approximately = (1+w), define firm targets for observational tests of the physics of dark energy.
authors.affiliation: Department of Physics & Astronomy, Dartmouth College, Hanover, New Hampshire 03755, USA.
authors.forename: R R
authors.initials: RR
authors.lastname: Caldwell
authors.forename: Eric V
authors.initials: EV
authors.lastname: Linder