Theoretical models of dark energy

Abstract

Observations of high redshift type Ia supernovae indicate that the universe is accelerating, fueled by an unknown form of 'dark energy' having large negative pressure p<0. The simplest example of dark energy is the cosmological constant (ρ=−ρ≡−Λ/8ρG). The cosmological constant arises at a fundamental level from one-loop quantum effects which generate a δ-term many orders of magnitude larger than the observed value of dark energy ∼ 10⁻⁴⁷ GeV⁴. This leads to the 'cosmological constant problem'. Dynamical models of dark energy include scalar fields with exponential and power law potentials. Dark energy can also be generated in extra-dimensional 'braneworld' models. Model-independent methods which attempt to reconstruct dark energy from supernova observations are discussed.