In the on-shell formulation of D = 5 , N = 2 supergravity, compactified on S 1 /Z 2 , we extend the results of Mirabelli and Peskin describing the interaction of the bulk fields with matter which is assumed to be confined on the brane. The novel characteristics of this approach are : Propagation of both gravity and gauge fields in the bulk, which offers an alternative for a unified description of models in extra dimensions and use of the on-shell formulation avoiding the complexity of offshell schemes which involve numerous auxiliary fields. We also allow for nontrivial superpotential interactions of the chiral matter fields.The method we employ uses the Nöther procedure and our findings are useful for building models advocating propagation of the gauge degrees of freedom in the bulk, in addition to gravity.
We investigate the cosmological inflation in a class of supergravity models that are generalizations of non-supersymmetric R 2 models. Although such models have been extensively studied recently, especially after the launch of the PLANCK and BICEP2 data, the class of models that can be constructed has not been exhausted. In this note, working in a supergravity model that is a generalization of Cecotti's model, we show that the appearance of new superpotential terms, which are quadratic in the superfield Λ that couples to the Ricci supermultiplet, alters substantially the form of the scalar potential. The arising potential has the form of the Starobinsky potential times a factor that is exponential in the inflaton field and dominates for large inflaton values. We show that the well-known Starobinsky inflation scenario is maintained only for unnaturally small fine-tuned values of the coupling describing the Λ 2 superpotential terms. A welcome feature is the possible increase of the tensor to scalar ratio r, within the limits set by the new Planck and BICEP2 data.
We consider a five-dimensional supergravity model with SU (5) gauge symmetry and the minimal field content. Studying the arising scalar potential we find that the gauging of the U (1) R symmetry of the five-dimensional supergravity causes instabilities. Lifting the instabilities the vacua are of Anti-de-Sitter type and SU (5) is broken along with supersymmetry. Keeping the U (1) R ungauged the potential has flat directions along which supersymmetry is unbroken.
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