Phase structure and phase transitions of the SU(2) x O(N) symmetric scalar field theory

Symmetry breaking patterns are explored in an extended model of electroweak Higgs sector consisting of an SU(2) doublet scalar field interacting with an N-component SU(2) singlet field, in the $N \to \infty$ limit. The detailed investigation is focused on potentials possessing classically only the SU(2) x O(N) symmetric ground state. Mixing between the Higgs-field and the hidden O(N) multiplet vanishes in this case even at next-to-leading order in N. Large regions of the extended space of Higgs couplings are found numerically compatible with present expectations on the nature of the Higgs sector, including also a consistent treatment of the finite temperature restoration of the SU(2) symmetry