  Supergravity, a locally supersymmetric gauge theory, may provide to describe
new physics beyond the Standard Model (BSM). In this sense, cosmological
applications of supergravity can be the arena for probing outcomes of
supergravity. It is also attractive that supergravity can appear as a
low-energy effective theory of superstrings, a possible candidate of quantum
gravity. Nevertheless, it is not trivial to build inflationary models in
supergravity due to difficulties arising mainly from the extremely constrained
form of supergravity scalar potentials, complicated structure of interaction
terms, and excessive scalar degrees of freedom. These obstructions generally
make it challenging to contrive a desirable inflationary trajectory, perform
the moduli stabilization to obtain the stable de-Sitter phase, and make extra
scalars to be much heavier than the Hubble scale to get single field inflation.
Besides, supergravity predicts many non-renormalizable interactions. It thus
arises as effective field theory (EFT) which can be valid only up to typical
energies $E$ below its ultraviolet cutoff scale $\Lambda_{cut}$, and up to some
accuracy of $(E/\Lambda_{cut})^n$ that we desire. We note that these
non-renormalizable terms may affect physics during and/or after inflation. From
such points of view, it is very important in supergravity to find the method
for relaxing the scalar potentials, and flexible scalar field dynamics
(particularly for inflaton), and examine self-consistency at the quantum level.
In this thesis, therefore, we construct locally supersymmetric effective field
theories of inflation (with KKLT string background) by taking into account
recently-proposed reformulations of $\mathcal{N}=1$ supergravity that can
enlarge the space of scalar potentials.
