Lambda-CDM model
The simplest explanation for dark energy is that it is a cosmological constant or vacuum energy; in this case . This leads to the Lambda-CDM model, which has generally been known as the Standard Model of Cosmology from 2003 through the present, since it is the simplest model in good agreement with a variety of recent observations. Riess "et al." found that their results from supernova observations favoured expanding models with positive cosmological constant () and a current accelerated expansion ().