Higgs phenomenology in the Stealth Doublet Model

Abstract

We analyze a model for the Higgs sector with two scalar doublets and a $Z_2$ symmetry that is manifest in the Yukawa sector but broken in the potential. Thus, one of the doublets breaks the electroweak symmetry and has tree-level Yukawa couplings to fermions, whereas the other doublet has no vacuum expectation value and no tree-level couplings to fermions. Since the $Z_2$ 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 $Z_2$ 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 charged scalar $H^{\pm }$ and the CP-odd scalar $A$ couple to fermions at one-loop level. We compute the decays of $H^{\pm }$ and $A$ and in particular the one-loop decays $A\to f\bar{f}$, $H^{\pm }\to f{\bar{f}}^{\prime }$, $H^{\pm }\to W^{\pm }Z$ and $H^{\pm }\to W^{\pm }\gamma$. We also describe how to calculate and renormalize such processes in our model. We find that if one of $H^{\pm }$ or $A$ is the lightest scalar, $H^{\pm }\to W^{\pm }\gamma$ or $A\to b\bar{b}$ are typically their respective dominating decay channels. Otherwise, the dominating decays of $H^{\pm }$ and $A$ are into a scalar and a vector. Due to the absence of tree-level fermion couplings for $H^{\pm }$ 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 $H^{\pm }\to W^{\pm }\gamma$ is realized in Nature, we estimate that there could be a considerable amount of such events in the present LHC data.

Comments: 40 pages, 25 figures. Version 4. Minor updates, references added. Version to appear in PRD