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Abstract

Under the assumption that the Standard Model is valid up to the Planck scale Λ_Pl ~10¹⁹ GeV, the quartic Higgs coupling exhibits near Λ_Pl a value remarkably close to zero. It is tempting to consider this feature as a manifestation of boundary conditions imposed by the embedding theory of gravity. In a stringy context this observation has recently been interpreted in terms of the scalar potential being invariant under a constant shift of the Higgs _eld at the Planck scale. In general, such boundary conditions are of special interest in the study of radiatively induced symmetry breaking in models with classical conformal invariance, as the Planck scale is connected to the breaking scale via the running of the scalar couplings. In this thesis, the Coleman-Weinberg symmetry breaking of the minimal classically conformally invariant left-right (LR) symmetric model is reconsidered in the presence of a shift symmetry which is generalized to the case of the LR symmetry. Within the restricted parameter space imposed by the shift symmetry, a large hierarchy between the LR breaking scale and the Planck scale can be generated. In order to stabalize the electroweak-scale as well, the model is extended by two fermionic representations, which contribute to the running of the scalar couplings.