The case for the cosmological constant

Abstract

I present a short overview of current observational results and theoretical models for a cosmological constant. The main motivation for invoking a small cosmological constant (or ∧-term) at the present epoch has to do with observations of high redshift Type Ia supernovae which suggest an accelerating universe. A flat accelerating universe is strongly favoured by combining supernovae observations with observations of CMB anisotropies on degree scales which give the 'best-fit' values Τ_∧ ≅ 0.7 and Τ_m ≅ 0.3. A time dependent cosmological ∧-term can be generated by scalar field models with exponential and power law potentials. Some of these models can alleviate the 'fine tuning' problem which faces the cosmological constant.