Dark energy from $\alpha$-attractors: phenomenology and observational
  constraints
  The possibility of linking inflation and late cosmic accelerated expansion
using the $\alpha$-attractor models has received increasing attention due to
their physical motivation. In the early universe, $\alpha$-attractors provide
an inflationary mechanism compatible with Planck satellite CMB observations and
predictive for future gravitational wave CMB modes. Additionally
$\alpha$-attractors can be written as quintessence models with a potential that
connects a power law regime with a plateau or uplifted exponential, allowing a
late cosmic accelerated expansion that can mimic behavior near a cosmological
constant. In this paper we study a generalized dark energy $\alpha$-attractor
model. We thoroughly investigate its phenomenology, including the role of all
model parameters and the possibility of large-scale tachyonic instability
clustering. We verify the relation that $1+w\sim 1/\alpha$ (while the
gravitational wave power $r\sim\alpha$) so these models predict that a
signature should appear in either the primordial B-modes or in late time
deviation from a cosmological constant. We constrain the model parameters with
current datasets, including the cosmic microwave background (Planck 2015
angular power spectrum, polarization and lensing), baryon acoustic oscillations
(BOSS DR12) and supernovae (Pantheon compressed). Our results show that
expansion histories close to a cosmological constant exist in large regions of
the parameter space, not requiring a fine-tuning of the parameters or initial
conditions.
