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Article Contents

ABSTRACT

1.INTRODUCTION

1.1.The many faces of the cosmological constant

1.2.A brief history of cosmological constant

2.FRAMEWORK OF STANDARD COSMOLOGY

2.1.Kinematics of the Friedmann model

2.2.Dynamics of the Friedmann model

2.3.Composition of the universe

2.4.Geometrical features of a universe with a cosmological constant

3.EVIDENCE FOR A NON-ZERO COSMOLOGICAL CONSTANT

3.1.Observational evidence for accelerating universe

3.2.Age of the universe and cosmological constant

3.3.Gravitational lensing and the cosmological constant

3.4.Other geometrical tests

4.MODELS WITH EVOLVING COSMOLOGICAL "CONSTANT"

4.1.Parametrized equation of state and cosmological observations

4.2.Theoretical models with time dependent dark energy: cosmic degeneracy

5.STRUCTURE FORMATION IN THE UNIVERSE

5.1.Linear evolution of perturbations

5.2.Nonlinear growth of perturbations

5.3.Structure formation and constraints on dark energy

6.CMBR ANISOTROPIES

7.REINTERPRETING THE COSMOLOGICAL CONSTANT

7.1.Cosmological constant as a Lagrange multiplier

7.2.Cosmological constant as a constant of integration

7.3.Cosmological constant as a stochastic variable

7.4.Anthropic interpretation of the cosmological constant

7.5.Probabilistic interpretation of the cosmological constant

8.RELAXATION MECHANISMS FOR THE COSMOLOGICAL CONSTANT

9.GEOMETRICAL STRUCTURE OF THE DE SITTER SPACETIME

10.HORIZONS, TEMPERATURE AND ENTROPY

10.1.The connection between thermodynamics and spacetime geometry

10.2.Temperature of horizons

10.3.Entropy and energy of de Sitter spacetime

10.4.Conceptual issues in de Sitter thermodynamics

11.COSMOLOGICAL CONSTANT AND THE STRING THEORY

REFERENCES