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We consider a model for the Higgs sector with two scalar doublets and a softly broken Z₂ symmetry, the Stealth Doublet Model. This model can be seen as a generalization of the Inert Doublet Model. One of the doublets is the Higgs doublet that participates in electroweak symmetry breaking and couples to fermions. The other doublet does not couple to fermions at tree level and does not acquire a vacuum expectation value. The broken Z₂ symmetry leads to interesting phenomenology such as mixing between the two doublets and charged and CP-odd scalars that can be light and have unusual decay channels. We present theoretical and experimental constraints on the model and consider the recent observation of a Higgs boson at the LHC. The data on the H→ γγ channel can be naturally accommodated in the model, with either the lightest or the heaviest CP-even scalar playing the role of the observed particle.

We analyze a model for the Higgs sector with two scalar doublets and a softly broken Z2 symmetry. One of the doublets breaks the electroweak symmetry and has tree-level Yukawa couplings to fermions. The other doublet has no vacuum expectation value and no tree-level couplings to fermions. Because the Z2 parity is broken the two doublets can mix, which leads to a distinct and novel phenomenology. This Stealth Doublet Model can be seen as a generalization of the Inert Doublet Model with a broken Z2 symmetry. We outline the model and present constraints from theory, electroweak precision tests and collider searches, including the recent observation of a Higgs boson at the LHC. The CP-odd scalar A and the charged scalar H± couple to fermions at one-loop level. We compute the decays of A and H± and in particular the one-loop decays A→ff¯, H±→ff¯′, H±→W±Z and H±→W±γ. We also describe how to calculate and renormalize such processes in our model. We find that if one of H± or A is the lightest scalar, H±→W±γ or A→bb¯ are typically their respective dominating decay channels. Otherwise, the dominating decays of H± and Aare into a scalar and a vector. Due to the absence of tree-level fermion couplings for H± and A, we consider pair production and associated production with vector bosons and scalars at the LHC. If the parameter space of the model that favors H±→W±γ is realized in Nature, we estimate that there should be a considerable amount of such events in the present LHC data.

In light of the recent discovery of a neutral Higgs boson, Hobs, with a mass near 125 GeV, we reassess the LHC discovery potential of a charged Higgs boson, H±, in the W±Hobs decay channel. This decay channel can be particularly important for a H± heavier than the top quark, when it is produced through the pp→tH± process. The knowledge of the mass of Hobsprovides an additional handle in the kinematic selection when reconstructing a Breit-Wigner resonance in the Hobs→bb¯ decay channel. We consider some extensions of the Standard Model Higgs sector, with and without supersymmetry, and perform a dedicated signal-to-background analysis to test the scope of this channel for the LHC running at design energy (14 TeV), for 300/fb (standard) and 3000/fb (high) integrated luminosities. We find that, while this channel does not show much promise for a supersymmetric H± state, significant portions of the parameter spaces of several two-Higgs doublet models are testable.

We confront the general, CP-conserving, two-Higgs-doublet model (2HDM) with Yukawa couplings of Types I–IV with all the data present from run-I of the LHC. For the allowed regions of parameter space, we investigate to what extent there can still exist relatively light scalars, and under which conditions they may be within discovery reach for upcoming LHC runs.