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Battye, R. A., Brawn, G. D., & Pilaftsis, A. (2011). Vacuum topology of the two Higgs doublet model. J. High Energy Phys., 08(8), 020–75pp.
Abstract: We perform a systematic study of generic accidental Higgs-family and CP symmetries that could occur in the two-Higgs-doublet-model potential, based on a Majorana scalar-field formalism which realizes a subgroup of GL(8, C). We derive the general conditions of convexity and stability of the scalar potential and present analytical solutions for two non-zero neutral vacuum expectation values of the Higgs doublets for a typical set of six symmetries, in terms of the gauge-invariant parameters of the theory. By means of a homotopy-group analysis, we identify the topological defects associated with the spontaneous symmetry breaking of each symmetry, as well as the massless Goldstone bosons emerging from the breaking of the continuous symmetries. We find the existence of domain walls from the breaking of Z(2), CP1 and CP2 discrete symmetries, vortices in models with broken U(1)(PQ) and CP3 symmetries and a global monopole in the SO(3)(HF)-broken model. The spatial profile of the topological defect solutions is studied in detail, as functions of the potential parameters of the two-Higgs doublet model. The application of our Majorana scalar-field formalism in studying more general scalar potentials that are not constrained by the U(1)(Y) hypercharge symmetry is discussed. In particular, the same formalism may be used to properly identify seven additional symmetries that may take place in a U(1)(Y)-invariant scalar potential.
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Filipuzzi, A., Portoles, J., & Ruiz-Femenia, P. (2012). Zeros of the W(L)Z(L) -> W(L)Z(L) amplitude: where vector resonances stand. J. High Energy Phys., 08(8), 080–22pp.
Abstract: A Higgsless electroweak theory may be populated by spin-1 resonances around E similar to 1 TeV as a consequence of a new strong interacting sector, frequently proposed as a tool to smear the high-energy behaviour of scattering amplitudes, for instance, elastic gauge boson scattering. Information on those resonances, if they exist, must be contained in the low-energy couplings of the electroweak chiral effective theory. Using the facts that: i) the scattering of longitudinal gauge bosons, W-L, Z(L), can be well described in the high-energy region (E >> M-W) by the scattering of the corresponding Goldstone bosons (equivalence theorem) and ii) the zeros of the scattering amplitude carry the information on the heavier spectrum that has been integrated out; we employ the O(p(4)) electroweak chiral Lagrangian to identify the parameter space region of the low-energy couplings where vector resonances may arise. An estimate of their masses is also provided by our method.
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