Supergravity

"Two developments in the late 1960s and early 1970s set the stage for supergravity. First the standard model took shape and was decisively confirmed by experiments. The key theoretical concept underlying this process was gauge symmetry, the idea that symmetry transformations act independently at each point of spacetime. ... The other development was global (also called rigid) supersymmetry ... It is the unique framework that allows fields and particles of different spin to be unified in representations of an algebra system called a superalgebra."

"Supergravity is a theory of gravity which has supersymmetry, a symmetry between bosons and fermions. Supersymmetry in supergravity is a local symmetry like the gauge symmetry in the standard theory of particle physics. The gauge field of the local supersymmetry is the Rarita-Schwinger field, which represents a particle with spin called a graviton. Supersymmetry also has a local symmetry under the general coordinate transformation, whose gauge field is the gravitational field. An important role of supergravity is in its relation to superstring theory. ... Supergravity provides a low energy effective theory of the massless sector of superstring theory and can be used to study its low energy properties."

"Inflation can be caused by the potential energy of a scalar field. Such a potential must be relatively flat in order to guarantee long duration of inflation and small deviation of scale invariance of primordial density fluctuations. However, the flatness of the scalar potential can be easily destroyed by radiative corrections. One of the leading theories to protect a scalar field from radiative corrections is supersymmetry (SUSY), which also gives an attractive solution to the (similar) hierarchy problem of the standard model (SM) of particle physics as well as the unification of the three gauge couplings. In particular, its local version, supergravity, would govern the dynamics of the early Universe, when high energy physics was important. Thus, it is quite natural to consider inflation in the framework of supergravity. However, in fact, it is a non-trivial task to incorporate inflation in supergravity. This is mainly because a SUSY breaking potential term, which is indispensable to inflation, generally gives a would-be inflaton an additional mass, which spoils the flatness of an inflation potential ..."