Quintessential Inflation with $\alpha$-attractors
  A novel approach to quintessential inflation model building is studied,
within the framework of $\alpha$-attractors, motivated by supergravity
theories. Inflationary observables are in excellent agreement with the latest
CMB observations, while quintessence explains the dark energy observations
without any fine-tuning. The model is kept intentionally minimal, avoiding the
introduction of many degrees of freedom, couplings and mass scales. In stark
contrast to $\Lambda$CDM, for natural values of the parameters, the model
attains transient accelerated expansion, which avoids the future horizon
problem, while it maintains the field displacement mildly sub-Planckian such
that the flatness of the quintessential tail is not lifted by radiative
corrections and violations of the equivalence principle (fifth force) are under
control. In particular, the required value of the cosmological constant is near
the eletroweak scale. Attention is paid to the reheating of the Universe, which
avoids gravitino overproduction and respects nucleosynthesis constraints.
Kination is treated in a model independent way. A spike in gravitational waves,
due to kination, is found not to disturb nucleosynthesis as well.
