Cosmological constant vs. quintessence

Abstract

There is some evidence that the Universe is presently undergoing accelerating expansion. This has restored some credit to the scenarios with a non-vanishing cosmological constant. From the point of view of a theory of fundamental interactions, one may argue that a dynamical component with negative pressure is easier to achieve. As an illustration, the quintessence scenario is described and its shortcomings are discussed in connection with the nagging ``cosmological constant problem''.

Comments: 28 pages, 2 figures, lectures at Les Houches summer school 'The early Universe" and Peyresq 4 meeting, July 1999