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In many models, stability of dark matter particles is protected by a conserved Z_2 quantum number. However dark matter can be stabilized by other discrete symmetry groups, and examples of such models with custom-tailored field content have been proposed. Here we show that electroweak symmetry breaking models with N Higgs doublets can readily accommodate scalar dark matter candidates stabilized by groups Z_p with any $p le 2^{N-1}$, leading to a variety of kinds of microscopic dynamics in the dark sector. We give examples in which semi-annihilation or multiple semi-annihilation processes are allowed or forbidden, which can be especially interesting in the case of asymmetric dark matter.
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We show that there are regions of parameter space in multi-scalar doublet models where, in the first few hundred inverse femtobarns of data, the new charged and neutral scalars are not directly observable at the LHC and yet the Higgs decay rate to b bbar is changed significantly from its standard model value. For a light Higgs with a mass less than 140 GeV, this can cause a large change in the number of two photon and tau tau Higgs decay events expected at the LHC compared to the minimal standard model. In the models we consider, the principle of minimal flavor violation is used to suppress flavor changing neutral currents. This paper emphasizes the importance of measuring the properties of the Higgs boson at the LHC; for a range of parameters the model considered has new physics at the TeV scale that is invisible, in the first few hundred inverse femtobarns of integrated luminosity at the LHC, except indirectly through the measurement of Higgs boson properties.
We study a two scalar inert doublet model (IDMS$_3$) which is stabilized by a $S_3$ symmetry. We consider two scenarios: i) two of the scalars in each charged sector are mass degenerated due to a residual $Z_2$ symmetry, ii) there is no mass degeneracy because of the introduction of soft terms that break the $Z_2$ symmetry. We show that both scenarios provide good dark matter candidates for some range of parameters.
Models with two or more scalar doublets with discrete or global symmetries can have vacua with vanishing vacuum expectation values in the bases where symmetries are imposed. If a suitable symmetry stabilises such vacua, these models may lead to interesting dark matter candidates, provided that the symmetry prevents couplings among the dark matter candidates and the fermions. We analyse three-Higgs-doublet models with an underlying $S_3$ symmetry. These models have many distinct vacua with one or two vanishing vacuum expectation values which can be stabilised by a remnant of the $S_3$ symmetry which survived spontaneous symmetry breaking. We discuss all possible vacua in the context of $S_3$-symmetric three-Higgs-doublet models, allowing also for softly broken $S_3$, and explore one of the vacuum configurations in detail. In the case we explore, only one of the three Higgs doublets is inert. The other two are active, and therefore the active sector, in many aspects, behaves like a two-Higgs-doublet model. The way the fermions couple to the scalar sector is constrained by the $S_3$ symmetry and is such that the flavour structure of the model is solely governed by the $V_text{CKM}$ matrix which, in our framework, is not constrained by the $S_3$ symmetry. This is a key requirement for models with minimal flavour violation. In our model there is no CP violation in the scalar sector. We study this model in detail giving the masses and couplings and identifying the range of parameters that are compatible with theoretical and experimental constraints, both from accelerator physics and from astrophysics.
We study a fermionic dark matter model in which the interaction of the dark and visible sectors is mediated by Higgs portal type couplings. Specifically, we consider the mixing of a dark sector scalar with the scalars of a Two Higgs Doublet Model extension of the Standard Model. Given that scalar exchange will result in a spin-independent dark matter-nucleon scattering cross section, such a model is potentially subject to stringent direct detection constraints. Moreover, the addition of new charged scalars introduce non-trivial flavour constraints. Nonetheless, this model allows more freedom than a standard Higgs portal scenario involving a single Higgs doublet, and much of the interesting parameter space is not well approximated by a Simplified Model with a single scalar mediator. We perform a detailed parameter scan to determine the mass and coupling parameters which satisfy direct detection, flavour, precision electroweak, stability, and perturbativity constraints, while still producing the correct relic density through thermal freezeout.
We demonstrate how residual flavour symmetries, infrared signatures of symmetry breaking in complete models of flavour, can naturally forbid (or limit in a flavour specific way) flavour-changing neutral currents (FCNC) in multi-Higgs-doublet models (MHDM) without using mass hierarchies. We first review how this model-independent mechanism can control the fermionic mixing patterns of the Standard Model, and then implement the symmetries in the Yukawa sector of MHDM, which allows us to intimately connect the predictivity of a given flavour model with its ability to sequester FCNC. Finally, after discussing various subtleties of the approach, we sketch an $A_4$ toy model that realises an explicit example of these simplified constructions.
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