Building Supergravity Quintessence Model
  It was recently pointed out that the cosmological constant (even metastable
one) belongs to the so-called "swampland" and hence cannot be obtained as the
low-energy limit of string theory that requires $|\nabla V| > c V$. If true,
the dark energy needs to be described by an evolving scalar field, i.e.,
quintessence with $w>-1$ within supergravity. However, the large hierarchy
between the supersymmetry breaking scale and the energy scale of dark energy
imposes a challenge on building quintessence models in supergravity as the
quintessence field typically acquires a mass of order the gravitino mass. We
investigate two approaches to circumvent this obstacle. One is imposing shift
symmetry to the quintessence sector, and we demonstrate any quintessence
potential can be embedded into supergravity and the fifth force constraint
gives little limit on quintessence field displacement, leading to possible
observational signature $w>-1$. The structure is stable against quantum
corrections. A particular example can address the cosmic coincidence problem.
The other approach is sequestered supergravity, and the stability requirement
strongly constrains the form of the Kahler potential and superpotential, and
the quintessence field displacement is typically much smaller than Planck mass.
In addition, to satisfy the fifth force constraint, the quintessence field
displacement is further restricted in the sequestered case, requiring $c \ll
1$.
