Phase transition gravitational waves from pseudo-Nambu-Goldstone dark matter and two Higgs doublets

Abstract

We investigate the potential stochastic gravitational waves from first-order electroweak phase transitions in a model with pseudo-Nambu-Goldstone dark matter and two Higgs doublets. The dark matter candidate can naturally evade direct detection bounds, and can achieve the observed relic abundance via the thermal mechanism. Three scalar fields in the model obtain vacuum expectation values, related to phase transitions at the early Universe. We search for the parameter points that can cause first-order phase transitions, taking into account the existed experimental constraints. The resulting gravitational wave spectra are further evaluated. Some parameter points are found to induce strong gravitational wave signals, which have the opportunity to be detected in future space-based interferometer experiments LISA, Taiji, and TianQin.

Reconciling Higgs physics and pseudo-Nambu-Goldstone dark matter in the S2HDM using a genetic algorithm

“…While the S2HDM was already studied in regards to the DM phenomenology and its cosmological history in refs. [29,36,46], a careful treatment of the S2HDM taking into account the large number of constraints has not been carried out yet. In our analysis we will demonstrate that the combined consideration of the experimental and theoretical constraints is crucial in order to make reliable predictions for the phenomenology of the S2HDM.…”

“…We will use this value as an upper limit on the relic abundance of χ in our analysis, taking into consideration that in case the relic abundance of χ is smaller than (Ωh 2 ) Planck there is room for additional (particle or astrophysical) contributions to the relic abundance. We focus the analysis on the Higgs funnel region with DM masses of 40 ≤ m χ ≤ 80, where there are good prospects to be able to explain most (or all) of the observed DM relic abundance via the thermal freeze-out of χ [14,23,25,29,36]. For the theoretical prediction of the relic abundance, we wrote an S2HDM modelfile for the Mathematica package FeynRules v.2 [109][110][111], which we utilized to obtain a CalcHEP [112] input for the public code MicrOMEGAs v.5 [113] written in C and Fortran.…”

“…A particle that naturally has this feature is the so-called pseudo-Nambu-Goldstone boson (pNG) DM [14][15][16][17][18][19][20]. As a result, BSM models that predict the existence of a stable pNG in order to account for the DM relic abundance have recently gained a lot of attention [21][22][23][24][25][26][27][28][29][30].…”

“…One of such possibilities is that pNG DM can be incorporated into 2 Higgs doublet models (2HDM) (see ref. [31] for a review), in which, in contrast to the pNG DM model with only one Higgs doublet [32], a first-order EW phase transition can be realized [29,33]. Such a transition provides a departure from thermal equilibrium, required to explain the matter-antimatter asymmetry via the mechanism of EW baryogenesis [34,35].…”

“…Such a transition provides a departure from thermal equilibrium, required to explain the matter-antimatter asymmetry via the mechanism of EW baryogenesis [34,35]. A cosmological first-order phase transition can also source the formation of a stochastic gravitational-wave background that could be observable at future space-based gravitational-wave interferometers, such as LISA [29]. Moreover, we emphasize that in the S2HDM the presence of the second Higgs doublet gives rise to two additional neutral and two charged scalars.…”