Cosmological impact of redshift drift measurements
  The redshift drift is a model-independent probe of fundamental cosmology, but
choosing a fiducial model one can also use it to constrain the model
parameters. We compare the constraining power of redshift drift measurements by
the Extremely Large Telescope (ELT), as studied by Liske {\it et al.} (2008),
with that of two recently proposed alternatives: the cosmic accelerometer of
Eikenberry {\it et al.} (2020), and the differential redshift drift of Cooke
(2020). We find that the cosmic accelerometer with a 6-year baseline leads to
weaker constraints than those of the ELT (by $60\%$), but with identical time
baselines it outperforms the ELT by up to a factor of 6. The differential
redshift drift always performs worse that the standard approach if the goal is
to constrain the matter density, but it can perform significantly better than
it if the goal is to constrain the dark energy equation of state. Our results
show that accurately measuring the redshift drift and using these measurements
to constrain cosmological parameters are different merit functions: an
experiment optimized for one of them will not be optimal for the other. These
non-trivial trade-offs must be kept in mind as next generation instruments
enter their final design and construction phases.
