CP in the dark

Abstract

We build a model containing two scalar doublets and a scalar singlet with a specific discrete symmetry. After spontaneous symmetry breaking, the model has Standard Model-like phenomenology, as well as a hidden scalar sector which provides a viable dark matter candidate. We show that CP violation in the scalar sector occurs exclusively in the hidden sector, and consider possible experimental signatures of this CP violation. In particular, we study contribution to anomalous gauge couplings from the hidden scalars.PACS numbers: I. INTRODUCTIONThe LHC discovery of a scalar with mass of 125 GeV [1, 2] completed the Standard Model particle content. The fact that precision measurements of the properties of this particle [3,4] indicate that it behaves very much in a Standard Model (SM)-like manner is a further confirmation of the validity and effectiveness of that model. Nonetheless, the SM leaves a lot to be explained, and many extensions of the theory have been proposed to attempt to explain such diverse phenomena as the existence of dark matter, the observed universal matter-antimatter asymmetry and others. In particular, numerous SM extensions consist of enlarged scalar sectors, with singlets, both real and complex, being added to the SM Higgs doublet [5][6][7][8][9][10][11][12][13]; or doublets, the simplest example of which is the two-Higgs doublet model (2HDM) [14,15]. Certain versions of singlet-doublet models provide dark matter candidates, as does the Inert version of the 2HDM (IDM) [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Famously, the 2HDM was introduced in 1973 by Lee to allow for the possibility of spontaneous CP violation. But models with dark matter candidates and extra sources of CP violation (other than the SM mechanism of CKM-matrix generated CP violation) are rare. Even rarer are models for which a "dark" sector exists, providing viable dark matter candidates, and where the extra CP violation originates exclusively in the "dark" sector. To the best of our knowledge, the only model with scalar CP violation in the dark sector is the recent work of Refs. [31,32], for which a three-doublet model was considered. The main purpose of Refs. [31,32] was to describe the dark matter properties of the model. In Ref. [33] an argument was presented to prove that the model is actually CP violating, adapting the methods of Refs. [34,35] for the complex 2HDM (C2HDM).In the current paper we will propose a model, simpler than the one in [31], but which boasts the same interesting properties, to wit: (a) a SM-like Higgs boson, h, "naturally" aligned due to the vacuum of the model preserving a discrete symmetry; (b) a viable dark matter candidate, the stability of which is guaranteed by the aforementioned vacuum and whose mass and couplings satisfy all existing dark matter search constraints; and (c) extra sources of CP *

CP violation from charged Higgs bosons in the three Higgs doublet model

“…6 In figures 1-2, we show the branching ratios (BRs) of H ± 2 (upper panels) and H ± 3 (lower panels) as a function of tan β, in the 3HDM Type-II, -X, -Y and the Democratic model. 7 In figure 1 we take M H ± 2 = 100 GeV and M H ± 3 = 150 GeV, while in figure 2 we 6 In all types of 3HDM except the Democratic one, taking the limit tan γ → ∞ (i.e., v3 → 0) recovers the corresponding 2HDM plus a third, inert, doublet. 7 We have used CalcHEP [20] to produce these plots.…”

“…At the same time, new CP-violating physics with direct couplings to quarks or leptons is becoming increasingly tightly constrained by measurements that set stringent upper limits on the electric dipole moments (EDMs) of the neutron [3] and electron [4]. These improved limits have led particle theorists to consider models in which the additional CP violation is sequestered in a hidden or dark sector that does not couple directly to SM fermions [5][6][7][8][9][10][11].…”

Dark origins of matter-antimatter asymmetry

“…An extended dark sector with a doublet plus a singlet could, in principle, accommodate dark CP-violation, however, the presence of the singlet dilutes the CP violating effects, since a singlet has no direct coupling to SM gauge bosons. As a result, the model fails to provide a DM candidate accounting for 100% of the observed relic density in the low mass region [33] We would like to point out that this is the reason Ref. [33] fails to find a DM candidate accounting for 100% of the observed relic density in the low mass region.…”

“…As a result, the model fails to provide a DM candidate accounting for 100% of the observed relic density in the low mass region [33] We would like to point out that this is the reason Ref. [33] fails to find a DM candidate accounting for 100% of the observed relic density in the low mass region. Furthermore, the collider signatures of dark CP violation through the ZZZ vertex and cross section asymmetries [31,49,50], in their model is considerably smaller.…”

“…As a result, a large region of the parameter space opens up to accommodate a DM candidate in agreement with cosmological and collider experiments. Note that a 3-Higgs doublet model (3HDM) with an extended inert sector is superior to a 2HDM plus a singlet scalar with an extended inert sector [33]; the amount of CP-violation is inevitably reduced due to the presence of the singlet and there exist fewer co-annihilation channels for the DM candidate.…”