Abstract
We analyse a possible adjustment of Twin Higgs models allowing to have broken electroweak (EW) symmetry at all temperatures below the sigma-model scale ∼ 1 TeV. The modification consists of increasing the Yukawa couplings of the twins of light SM fermions. The naturalness considerations then imply a presence of relatively light electroweak-charged fermions, which can be produced at the LHC, and decay into SM gauge and Higgs bosons and missing energy. Analysis of experimental bounds shows that such a modified model features an increased amount of fine-tuning compared to the original Twin Higgs models, but still less tuning than the usual pseudo-Nambu-Goldstone Higgs models not improved by Z2 twin symmetry. The obtained modification in the evolution of the EW symmetry breaking strength can, in particular, have interesting implications for models of EW baryogenesis, which we comment on.
Highlights
The main motivation for considering the Twin Higgs scenarios, with a field content significantly enlarged with respect to the SM, is a possibility to decrease the amount of fine tuning, needed to generate the separation between the EW scale and the scale of SM-charged new physics, which is pushed up by the collider experiments
The SNR Twin Higgs appears to be worse than the vanilla Twin Higgs scenarios but still better than the usual Goldstone Higgs models [30] not enhanced by a Z2 symmetry
We provide for the first time a concrete quantitative evaluation of the fine tuning necessary to accommodate the EW symmetry non-restoration at high temperature, which was not given much of attention previously
Summary
For various reasons the Standard Model is typically considered as an effective description, approximating the low-energy limit of some fundamental theory in the UV. In figure 2 we show three distinct types of the Higgs field evolution with temperature: EW symmetry restoration, behaviour with alternating hSM/T ≶ 1, and the trajectory with hSM/T > 1 In the latter two cases the Higgs field value growth with temperature is limited by the position of the minimum of the thermal potential induced by the twin fermions and gauge bosons, which is defined by mq,t,W (h) = 0, and corresponds to h = πf /2, or hSM = f. In this minimum the EW symmetry is maximally broken, while the twin EW symmetry is restored. The baryon asymmetry can be generated upon this confinement phase transition, if it is of the first order [45, 46], and remain unaffected by the sphaleron washout which is inefficient for hSM/T > 1
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