| Summary: | The thesis comprises reports of studies undertaken on three separate extensions of the Standard Model. It begins with an original introductory chapter, which introduces the theoretical background required to understand the motivation and broad definition of the concepts introduced in subsequent chapters. The first extension is a “bottom-up” minimal supersymmetric scenario, where the possibility of observing the gluino at a future high-energy linear <i>e</i><sup>+</sup><i>e<sup>-</sup> </i>collider is investigated. The second is a supersymmetric Standard Model derived from a five-dimensional warped supergravity, combining aspects of the MSSM and the Randall-Sundrum construction. The scenario is studied in the context of an effective theory, valid at energies below the scale of the compact fifth dimension. Possible observations of extra-dimensional effects on the scalar sector at a similar collider are investigated. Particular attention is paid to the mixing of scalars originating in the gravitational sector with those from the Higgs sector. The third extension is motivated by a recent attempt to solve the cosmological constant problem, in the framework of six-dimensional supergravity. In this scenario the compact dimensions are assumed to be flat, and of order ~1<i>m</i>m in size. This gives rise to a finely-spaced spectrum of Kaluza-Klein states which can be modelled by a modification of the space to incorporate an integration over these modes. The lowest-dimension interaction between bulk and brane fields is identified, and a possible search channel at a future linear collider is studied.
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