Cosmology with Phase 1 of the Square Kilometre Array; Red Book 2018:
  Technical specifications and performance forecasts
  We present a detailed overview of the cosmological surveys that will be
carried out with Phase 1 of the Square Kilometre Array (SKA1), and the science
that they will enable. We highlight three main surveys: a medium-deep continuum
weak lensing and low-redshift spectroscopic HI galaxy survey over 5,000 sqdeg;
a wide and deep continuum galaxy and HI intensity mapping survey over 20,000
sqdeg from z = 0.35 - 3; and a deep, high-redshift HI intensity mapping survey
over 100 sqdeg from z = 3 - 6. Taken together, these surveys will achieve an
array of important scientific goals: measuring the equation of state of dark
energy out to z ~ 3 with percent-level precision measurements of the cosmic
expansion rate; constraining possible deviations from General Relativity on
cosmological scales by measuring the growth rate of structure through multiple
independent methods; mapping the structure of the Universe on the largest
accessible scales, thus constraining fundamental properties such as isotropy,
homogeneity, and non-Gaussianity; and measuring the HI density and bias out to
z = 6. These surveys will also provide highly complementary clustering and weak
lensing measurements that have independent systematic uncertainties to those of
optical surveys like LSST and Euclid, leading to a multitude of synergies that
can improve constraints significantly beyond what optical or radio surveys can
achieve on their own. This document, the 2018 Red Book, provides reference
technical specifications, cosmological parameter forecasts, and an overview of
relevant systematic effects for the three key surveys, and will be regularly
updated by the Cosmology Science Working Group in the run up to start of
operations and the Key Science Programme of SKA1.
