Phase transitions and gravitational wave tests of pseudo-Goldstone dark matter in the softly broken 
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 scalar singlet model

We consider an extension of the Standard Model with a complex singlet scalar, where a global U(1) symmetry is explicitly broken to Z 3 symmetry. We study the two-step electroweak phase transition in the model and find that it can be of first-order if the heavy scalar mass falls in the range of 1-2 TeV and the mixing angle |θ| 0.2 (11.5 •). The Higgs signal strength measurements at the LHC, on the other hand, restrict the mixing angle |θ| 0.4 (23 •). Future colliders including high-luminosity LHC can probe the remaining parameter space of first-order phase transition in this scenario. After the U(1) symmetry breaking, the pseudo-Goldstone boson becomes a dark matter candidate due to a hidden Z 2 symmetry of the model. We find that the pseudo-Goldstone boson can make up a small fraction of the observed dark matter and escape from the constraints of current direct detection. We also show that the stochastic gravitational wave signals from the phase transition are potentially discoverable with future space-based interferometers.

Section: Jhep07(2020)082 Introductionmentioning

confidence: 94%

First-order electroweak phase transition in a complex singlet model with ℤ3 symmetry

Chiang

2020

“…[11,12]), the global U(1) symmetry is explicitly broken down to a Z 2 symmetry by the DM mass term. In this case, the electroweak phase transition is of second order [13]. If the U(1) symmetry is explicitly broken to Z 3 [14] or to nothing, the resulting cubic terms of the general model can induce, in part of the parameter space, strong first-order phase transitions [15][16][17] JHEP10(2020)080…”

Section: Introductionmentioning

confidence: 99%

Pseudo-Goldstone dark matter: gravitational waves and direct-detection blind spots

Alanne

Benincasa

Heikinheimo

et al. 2020

Self Cite

Pseudo-Goldstone dark matter is a thermal relic with momentum-suppressed direct-detection cross section. We study the most general model of pseudo-Goldstone dark matter arising from the complex-singlet extension of the Standard Model. The new U(1) symmetry of the model is explicitly broken down to a CP-like symmetry stabilising dark matter. We study the interplay of direct-detection constraints with the strength of cosmic phase transitions and possible gravitational-wave signals. While large U(1)-breaking interactions can generate a large direct-detection cross section, there are blind spots where the cross section is suppressed. We find that sizeable cubic couplings can give rise to a first-order phase transition in the early universe. We show that there exist regions of the parameter space where the resulting gravitational-wave signal can be detected in future by the proposed Big Bang Observer detector.

“…Such a situation can be circumvented if one can effectively suppress DM-nucleon scattering at zero momentum transfer without reducing DM annihilation at the freeze-out epoch. An appealing approach to achieve this is provided by Higgs-portal pseudo-Nambu-Goldstone boson (pNGB) DM models [7][8][9][10][11][12][13][14][15][16][17][18][19][20], where the DM candidate is a pNGB protected by a global symmetry which is softly broken by quadratic mass terms. The pNGB nature makes the tree-level DM-nucleon scattering amplitude vanish in the zero momentum transfer limit [7].…”

Section: Introductionmentioning

confidence: 99%

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

Zhen

Cai

Jiang

et al. 2021

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.