Dark energy constraints from ESPRESSO tests of the stability of
  fundamental couplings
  ESPRESSO is a high-resolution-ultra-stable spectrograph for the VLT, whose
commissioning will start in 2017. One of its key science goals is to test the
stability of nature's fundamental couplings with unprecedented accuracy and
control of possible systematics. A total of 27 nights of the ESPRESSO
Consortium's guaranteed time observations (GTO) will be spent in testing the
stability of the fine-structure constant and other fundamental couplings. A set
of 14 priority optimal targets have been selected for the GTO period. Here we
briefly discuss the criteria underlying this selection and describe the
selected targets, and then present detailed forecasts of the impact of these
measurements on fundamental physics and cosmology, focusing on dark energy
constraints and using future supernova type Ia surveys as a comparison point.
We show how canonical reconstructions of the dark energy equation of state are
improved by the extended redshift range enabled by these spectroscopic
measurements, and also quantify additional improvements foreseen for a future
ELT-HIRES instrument.
