Kinetically driven quintessence

Recently, a novel class of models for inflation has been found in which the inflationary dynamics is driven solely by (noncanonical) kinetic terms rather than by potential terms. As an obvious extension, we show that a scalar field with noncanonical kinetic terms alone behaves like an energy component which is time varying and has negative pressure presently, i. e. , quintessence. We present a model which has a constant equation of state, that is, a ``kinetic'' counterpart of the Ratra-Peebles model of a quintessence field with a potential term. We make clear the structure of the phase plane and show that the quintessential solution is a late-time attractor. We also give a model for the ``phantom'' component which has an equation of state with w=p/<-1.