Aspects of the gauge theoretical structure of gravity and supergravity

The nature of gravity as a spontaneously broken gauge theory is discussed and some of the implications this has had on the construction of supergravity theories are considered. Gravity is first examined as a classical gauge theory. Einstein's theory of gravitation is considered as a basis for a quantum theory and supersymmetry is introduced as a promising step towards a finite theory of gravitation. Cosmological and gravitino mass terms are obtained which may, with suitably chosen numerical coefficients, preserve local supersymmetry and which vanish after group contraction. Models based upon constrained, auxiliary Higgs fields are found to be so restricted that they can have no group contraction limit if they are to contain kinetic terms for the gravitino. Actions are constructed for matter multiplets coupled to supergravity. It is argued that only the adjoint multiplet may reduce to a flat space-time super symmetry multiplet and it is shown that it coincides with the massless vector multiplet. The coupling of the adjoint multiplet to the gauge fields is examined in detail and compared with previous approaches. In the absence of spinor fields the theory reduces to a non-minimal coupling of gravity to electromagnetism. The problems with obtaining a group contraction limit theory are demonstrated and non-linear actions for matter coupled to supergravity are discussed. (U.K.)