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

Abstract

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.

The Higgs-portal for dark matter: effective field theories versus concrete realizations

“…We also remark that one can accommodate a variant of this scenario in which the DM is a pseudo-Goldstone boson of the aforementioned global U( 1) symmetry [64][65][66]. Despite of its interesting phenomenology, especially for what concerns DM direct detection [67][68][69][70], we will not consider this scenario here.…”

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

“…Nevertheless, a study [12] showed that such phase transitions can only be of second order and impossible to produce stochastic GWs. Further studies tried to introduce extra terms to break the U(1) symmetry, e.g., the soft cubic terms [36], or the most general breaking terms [45]. These efforts successfully achieved first-order phase transitions (FOPTs) and stochastic GWs, but the essential merit of the vanishing tree-level DM-nucleon scattering in the zero momentum transfer limit is sacrificed.…”

Exploring direct detection suppressed regions in a simple 2-scalar mediator model of scalar dark matter

“…Many Higgs portal models have a second scalar that mixes with the Standard Model (SM) Higgs boson [7,9,10,12,14,17,[20][21][22][23]25,26,38,54,[58][59][60][61][62][63][64]. The mechanism leading to blind spots in such models is the destructive interference between the Higgs-like scalar and the second scalar in the direct detection cross section amplitude [9,10,12,17,20,21,23,26,54,61,63]. Given that detecting dark matter is the focus of a broad experimental program, we felt it useful to further explore regions of the parameter space that give rise to suppressed direct detection cross sections.…”

“…There are, however, many possible variations of this simple picture that can give rise to cancellations in the direct detection cross section. An incomplete list of possibilities appearing in the literature consists of the scalar portal being replaced with a pseudoscalar portal [22,55,[65][66][67][68][69][70][71][72], or having a complex scalar which gives rise to a second scalar portal [20,26,26,57,73,74], a two Higgs doublet model [22,23,55,63,64,[69][70][71][74][75][76][77], higher Higgs representations [78], or supersymmetric models [22,52,54,[79][80][81][82]. Before proceeding, we note that, given that we simply want to push the simplest of models as far as we could, we haven't dealt with the issue of UV completeness.…”

“…However, Gross et al [20] and Huitu et al [57] showed that they could make models very similar to ours UV complete by assuming the system is invariant under a global U (1) which is gauged in the UV-completeness. Other examples of similar UV complete models are [25,26].…”