PHYSICAL REVIEW D 101, 035001 (2020) - Gravitational wave signals of pseudo-Goldstone dark matter in the Z3 complex singlet model - Inspire HEP
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PHYSICAL REVIEW D 101, 035001 (2020) Gravitational wave signals of pseudo-Goldstone dark matter in the Z3 complex singlet model Kristjan Kannike ,* Kaius Loos,† and Martti Raidal ‡ National Institute of Chemical Physics and Biophysics, Rävala 10, Tallinn 10143, Estonia (Received 7 August 2019; accepted 14 January 2020; published 3 February 2020) We study pseudo-Goldstone dark matter in the Z3 complex scalar singlet model. Because the direct detection spin-independent cross section is suppressed, such dark matter is allowed in a large mass range. Unlike in the original model stabilized by a parity and due to the cubic coupling of the singlet, the Z3 model can accommodate first-order phase transitions that give rise to a stochastic gravitational wave signal potentially observable in future space-based detectors. DOI: 10.1103/PhysRevD.101.035001 I. INTRODUCTION admits two phases that produce a dark matter candidate. Firstly, the unbroken Z3 symmetry stabilizes S as a dark One of the best candidates for the dark matter (DM) is a matter candidate. Secondly, with the broken Z3 symmetry, scalar singlet [1,2]. The properties of singlet DM have been the imaginary part of S, denoted by χ, is still stable due to studied in detail [3–6] (see [7,8] for recent reviews; see also the S → S† symmetry of the Lagrangian. The main differ- Refs. therein). The nonobservation of dark matter by direct ence between the Z2 and Z3 pseudo-Goldstone DM models detection experiments [9–11], however, puts severe bounds is that the potential of the latter contains a cubic S3 term. on models of DM comprised of weakly interacting massive There are other possible cubic terms [21–23], but they do particles (WIMP), pushing the mass of the singlet scalar not respect the Z3 symmetry. DM—except around the Higgs resonance—over 1 TeV. To this date, the Z3 -symmetric complex singlet model A way to suppress the direct detection cross section is to has been studied in the unbroken phase. Originally, the consider as the DM candidate a pseudo-Goldstone with model was proposed in the context of neutrino physics [24]. derivative couplings to CP-even states [12] (the DM Detailed analysis of DM phenomenology was carried out in phenomenology of the imaginary part of the complex Ref. [25]. Indirect detection of Z3 DM was considered in scalar singlet was first considered in [3,13], but only in [26,27]. The cubic coupling can contribute to 3 → 2 scat- the Higgs resonance region). Because the velocity of DM tering for Z3 strongly interacting (SIMP) DM [28–31]. The particles in the Galaxy is small, the prospective signal is effects of early kinetic decoupling were studied in [32]. The suppressed by vanishing momentum transfer. This result Z3 symmetry has been considered as the remnant of a dark remains practically unaffected when loop corrections to the Uð1Þ local [33–35] or global [36] symmetry. In the direct detection cross section are taken into account unbroken phase, the direct detection cross section can also [14,15]. Despite that, it is possible for pseudo-Goldstone be suppressed if the DM relic density is determined by DM to show up at the LHC [16–19]. Pseudo-Goldstone semiannihilation processes [37–42]. However, the suppres- DM with two Higgs doublets was considered in [20]. sion is not as large as for pseudo-Goldstone DM. In this class of models, the global Uð1Þ symmetry is The discovery of gravitational waves (GWs) by the explicitly, but only softly, broken into a discrete subgroup LIGO experiment [43,44] opened a new avenue to probe which is then broken spontaneously. In Ref. [12], the Uð1Þ new physics. First-order phase transitions generate a group was explicitly broken into Z2 symmetry. We study stochastic GW background [45–47], which may be dis- the consequences of breaking Uð1Þ into Z3 . The model coverable in future space-based GW interferometers [48,49]. While the SM Higgs phase transition is a smooth * kristjan.kannike@cern.ch crossover [50,51] and does not generate a GW signal, in † models with an extended scalar sector, the first-order phase kaius.loos@gmail.com ‡ martti.raidal@cern.ch transition in the early Universe can become testable by observations. For a recent review on phase transitions and Published by the American Physical Society under the terms of GWs, see Ref. [52]. the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to GWs from beyond-the-SM physics with a scalar singlet the author(s) and the published article’s title, journal citation, have been studied in detail. These models admit a two-step and DOI. Funded by SCOAP3. phase transition that can be of the first order [53–60] and 2470-0010=2020=101(3)=035001(10) 035001-1 Published by the American Physical Society
KANNIKE, LOOS, and RAIDAL PHYS. REV. D 101, 035001 (2020) can potentially produce a measurable GW signal [61–72]. phase, the complex singlet S is a DM candidate, while in the However, in the Z2 pseudo-Goldstone model, all phase broken Z3 phase, it is its imaginary part, the pseudo- transitions leading to the correct vacuum are of the second Goldstone χ, which can be the DM. We concentrate on the order [73], yielding no stochastic GW signal and excluding latter case. (In order to avoid domain walls [75–79] due to the additional potentially powerful experimental test of this the broken Z3 , we can add to the potential a small term that class of the SM models. The phenomenology of phase explicitly breaks Z3 , such as the linear term in S, but transitions and GWs of the Z3 complex singlet model was otherwise does not change the dark matter phenomenology.) studied in detail in Ref. [74] for the case where only the Without a loss of generality, the vacuum expectation Higgs boson has a VEV in our vacuum. This work, value (VEV) of S can be taken to be real and positive, however, disregarded the singlet as a DM candidate, because the degenerate vacua, where χ has a nonzero VEV, because in the unbroken phase, a sizeable GW signal is are related to the real vacuum by Z3 transitions. This choice incompatible with the correct relic density. corresponds to a negative value of the parameter μ3. The goal of this paper is to study the nature of phase The stationary point conditions are transitions and GW signals in the complex scalar singlet model in which a Uð1Þ symmetry is softly broken into its hð2λH h2 þ 2μ2H þ λSH s2 Þ ¼ 0; ð3Þ Z3 subgroup. Just like in the Z2 case, the elastic scattering pffiffiffi cross section pseudo-Goldstone DM with matter can be sð4λS s2 þ 3 2μ3 s þ 4μ2S þ 2λSH h2 Þ ¼ 0: ð4Þ small enough for the DM to be well hidden from direct detection. We find, however, that unlike in the Z2 case, We see that the model admits four types of extrema: the strong first-order phase transitions can take place because origin as O ≡ ð0; 0Þ is fully symmetric; the vacuum the potential contains a cubic term. The resulting stochastic H ≡ ðvh ; 0Þ, with Higgs VEV only, spontaneously breaks GW background is potentially discoverable in future space- the electroweak symmetry; the vacuum S ≡ ð0; vs Þ, with S based detectors such as LISA and BBO. VEV only, spontaneously breaks Z3 ; our vacuum HS ≡ The paper is organized as follows. We introduce the ðvh ; vs Þ breaks both symmetries. model in Sec. II. Various theoretical and experimental The mass matrix of CP-even scalars in our HS vacuum constraints are discussed in Sec. III. DM relic density, is given by phase transitions, and the predictions for the direct detec- tion and GW signals are treated in Sec. IV. We conclude in 2λH v2 λSH vvs 2 Sec. V. The details on the effective potential and thermal M ¼ : ð5Þ corrections are relegated to the Appendix. λSH vvs 2λS v2s þ p3 ffiffi μ3 vs 2 2 The mass matrix (5) is diagonalized by an orthogonal II. Z3 COMPLEX SINGLET MODEL matrix, The most general renormalizable scalar potential of the Higgs doublet H and the complex singlet S, invariant under cos θ − sin θ O¼ ; ð6Þ the Z3 transformation H → H, S → ei2π=3 S, is given by sin θ cos θ V ¼ μ2H jHj2 þ λH jHj4 þ μ2S jSj2 þ λS jSj4 via diagðm21 ; m22 Þ ¼ OT M2 O. The mixing angle θ is μ given by þ λSH jSj2 jHj2 þ 3 ðS3 þ S†3 Þ; ð1Þ 2 λSH vvs where only the cubic μ3 term softly breaks a global Uð1Þ tan 2θ ¼ : ð7Þ λH v þ λS v2s − 4p3 ffiffi2 μ3 vs 2 symmetry. Notice that the Z3 symmetry precludes any quartic couplings that would result in a hard breaking of the The mixing of the CP-even states h and s will yield two Uð1Þ. The potential Eq. (1)—just like in the original Z2 CP-even mass eigenstates h1 and h2 The mass of the pseudo-Goldstone DM model—has an additional discrete pseudoscalar χ is, taking into account the extremum Z2 symmetry, S → S† . conditions, In the unitary gauge, we parametrize the fields as 0 9 v þ s þ iχ m2χ ¼ − pffiffiffi μ3 vs ; ð8Þ H ¼ vþh ; S¼ s : ð2Þ 2 2 pffiffi 2 2 which is proportional to μ3 as it explicitly breaks the Uð1Þ The S → S† is then equivalent to χ → −χ, which makes χ symmetry. stable even as the Z3 symmetry is broken. The model thus We express the potential parameters in terms of physical admits two different DM candidates: in the unbroken Z3 quantities in the zero-temperature vacuum, that is the 035001-2
GRAVITATIONAL WAVE SIGNALS OF PSEUDO-GOLDSTONE … PHYS. REV. D 101, 035001 (2020) masses m21 and m21 of real scalars, their mixing angle θ, tree-level values. The model is perturbative [86] if pseudoscalar mass m2χ , and the VEVs vh and vs , jλH j ≤ 23 π, jλS j ≤ π, and jλSH j ≤ 4π. We require that our HS vacuum be the global one: this m21 þ m22 þ ðm21 − m22 Þ cos 2θ implies that λH ¼ ; ð9Þ 4v2h 9m21 m22 m2χ < ; ð18Þ 3ðm21 þ m22 Þ þ 2m2χ þ 3ðm22 − m21 Þ cos 2θ m21 cos θ þ m22 sin2 θ 2 λS ¼ ; ð10Þ 12v2s which for sin θ ≈ 0 is approximated by mχ ≲ 3m2. This bound appears to be stronger than the constraint on the ðm21 − m22 Þ sin 2θ λSH ¼ ; ð11Þ cubic coupling from unitarity at finite-energy scattering. 2vs vh If the mass of x ≡ χ or h2 is less than mh =2, then the Higgs invisible decay width into this particle is given by 1 1 μ2H ¼ − ðm21 þ m22 Þ þ ðm2 − m21 Þ sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 4 4vh 2 g m2 × ðvh cos 2θ þ vs sin 2θÞ; ð12Þ Γh→xx ¼ hxx 1 − 4 2x ; ð19Þ 8π mh 1 1 1 μ2S ¼ − ðm21 þ m22 Þ þ m2χ þ ðm2 − m22 Þ with 4 6 4vs 1 × ðvs cos 2θ − vh sin 2θÞ; ð13Þ m2h þ m2χ gh1χχ ¼ ; ð20Þ pffiffiffi vS 2 2 m2χ μ3 ¼ − : ð14Þ 1 1 2 9 vs gh1h2 h2 ¼ 2 m þ m2 ðv cos θ þ vS sin θÞ vvS 2 h Both the Higgs doublet and the singlet will get a VEV, with 1 2 the Higgs VEV given by vh ¼ v ¼ 246.22 GeV. We þ vmχ cos θ sin 2θ: ð21Þ 6 identify h1 with the SM Higgs boson with mass m1 ¼ 125.09 GeV [80]. The invisible Higgs branching ratio is then given by III. THEORETICAL AND EXPERIMENTAL Γh→χχ þ Γh→h2 h2 BRinv ¼ ; ð22Þ CONSTRAINTS Γh1 →SM þ Γh→χχ þ Γh→h2 h2 We impose various theoretical and experimental con- which is constrained to be below about 0.24 at 95% straints on the parameter space of the model. confidence level [87,88] by direct measurements and below First of all, the potential (1) is bounded from below if about 0.17 by statistical fits of all Higgs couplings [89,90] pffiffiffiffiffiffiffiffiffiffi (decays of the resulting h2 into the SM may be visible [16], λH > 0; λS > 0; λSH þ 2 λH λS > 0: ð15Þ but these points are already excluded by direct detection in any case). In extended Higgs models [91], the mixing Secondly, we require the couplings to be unitary and phenomenology can be more complicated. perturbative. The unitarity constraints in the s → ∞ limit The mixing angle between h and s is constrained from are given by the measurements of the Higgs couplings at the LHC to j sin θj ≤ 0.5 for m2 ≲ mh and j sin θj ≤ 0.37 for m2 ≳ mh ; jλH j ≤ 4π; jλS j ≤ 4π; jλSH j ≤ 8π; ð16Þ for the latter case, we have an ever stronger constraint from qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi the mass of the W boson down to j sin θj ≤ 0.2 for larger j3λH þ 2λS 9λ2H − 12λH λS þ 4λ2S þ 2λ2SH j ≤ 8π; ð17Þ values of m2 [92]. Last, but not least, we require that the relic density of χ be equal to the value ΩDM h2 ¼ 0.120 0.001 from recent where the last condition, in the λSH ¼ 0 limit, yields jλH j ≤ Planck data [93]. 4 3π and jλS j ≤ 2π. We also calculate unitarity constraints at finite energy with the help of the latest version [81] of the IV. DIRECT DETECTION AND SARAH package [82–85]. Scattering at finite energy allows GRAVITATIONAL WAVE SIGNALS us to set a bound on the cubic coupling μ3 . To ensure the validity of perturbation theory, loop For the scan of the parameter space, we choose mχ , m2 , corrections to couplings should be smaller than their and sin θ as the free parameters, while vs is used to fit the DM 035001-3
KANNIKE, LOOS, and RAIDAL PHYS. REV. D 101, 035001 (2020) relic density. We generate the free parameter values in the μ2H ðTÞ ¼ μ2H þ cH T 2 ; μ2S ðTÞ ¼ μ2H þ cS T 2 ; ð26Þ following ranges: mχ ∈½25;1000GeV, m2 ∈½25;4000GeV, and sin θ ∈ ½−0.5; 0.5. We use the micrOMEGAs package [94] with the coefficients, to fit the DM relic density and CosmoTransitions [95] for the 1 calculation of phase transitions and the Euclidean action to cH ¼ ð9g2 þ 3g02 þ 12y2t þ 24λH þ 4λSH Þ; ð27Þ 48 determine tunneling rates. The stochastic gravitational wave signals were calculated using the formulas of Ref. [96] for the 1 cS ¼ ð2λS þ λSH Þ: ð28Þ nonrunaway case. At the temperature T at which gravita- 6 tional waves are being produced, the spectrum is a function of For numerical calculations of gravitational wave signals, the parameters, the exact expression of the thermal potential is used. ρvac We present in Fig. 1, the results of our scans for the direct α¼ ; ð23Þ ρrad detection signal. In the left panel, we present, for illus- tration, the behavior of spin-independent direct detection where ρrad ¼ g π 2 T 4 =30 and g is the number of relativistic cross section σ SI as a function of DM mass mχ for fixed degrees of freedom (d.o.f.) in the plasma at temperature T , values of m2 ¼ 300 GeV and sin θ ¼ 0.05. Red lines show and the current limit from the XENON1T experiment [10] and the future bound from the projected XENONnT experiment [97]. β dS While the usual Z2 scalar singlet DM is excluded below ¼ T ; ð24Þ H dT T OðTeVÞ masses, except for the Higgs resonance region, the suppression of the pseudo-Goldstone cross section in this where S is the Euclidean action of a critical bubble. model allows for lighter DM candidates. The two pro- The micrOMEGAs is also used to compute predictions for nounced dips in the cross section are given by the Higgs direct detection signals, to which we add the tiny loop resonance at mh =2 and the h2 resonance at m2 =2. correction. Unlike in the Z2 pseudo-Goldstone DM model, The direct detection signal varies over a wide range and the tree-level direct detection DM amplitude contains a is proportional to μ23 . Because the amplitude is proportional term that does not vanish at zero momentum transfer, so to sin θ cos θ, larger mixing angles also produce larger Add ðt ≈ 0Þ ∝ λSH μ3 : ð25Þ direct detection signal. The right panel in Fig. 1 presents the results of the whole scan, coded in grey-scale by the mixing For a large part of the parameter space, however, this term is angle j sin θj; empty points are excluded by the constraint small enough, which allows one to explain the negative on the Higgs invisible branching ratio. The points shown experimental results from DM direct detection experiments satisfy all other constraints with the exception of the for a wide range of pseudo-Goldstone DM masses. collider constraints [92] on j sin θj (as seen, most such In the high temperature approximation (A8), the mass points are already excluded by direct detection). Note that terms acquire thermal corrections, the BRinv can exclude points with mχ > mh =2, because the FIG. 1. Left panel: Spin-independent direct detection cross section σ SI as a function of the DM mass mχ for fixed m2 ¼ 300 GeV and sin θ ¼ 0.05. The bound from the XENON1T experiment is shown in red and the predicted sensitivity of the XENONnT experiment in dashed red. Right panel: Scatter plot of the results in ðmχ ; σ SI Þ plane in the grey-scale representing the dependence on j sin θj. The upper bound in σ SI is given by the requirement that the ðvh ; vs Þ minimum be the global one. In unfilled points, the Higgs invisible width surpasses the experimental limit. 035001-4
GRAVITATIONAL WAVE SIGNALS OF PSEUDO-GOLDSTONE … PHYS. REV. D 101, 035001 (2020) FIG. 2. Left panel: Scatter plot for the peak power of GWs vs the frequency together with the sensitivity curves of the LISA and BBO experiments. Light red points are forbidden and darker green points are allowed by the results of the XENON1T direct detection searches; both sets of points pass all other constraints, including the relic density. Right panel: The dependence of the peak power of GWs on the value of cubic coupling for the points that pass all constraints including direct detection. The color code shows the nature of the phase transition that gives the strongest signal: O → S in orange, S → S in dark blue, S → HS in cyan, HS → HS in yellow, H → HS in purple, O → H in red. Higgs boson can decay invisibly also to two h2 if it is light enough. Early kinetic decoupling [98,99] may additionally enhance BRinv several times [32], but, in practice, this would not change the parameter space of GW signals. In particular, all our points with a potentially measurable GW signal have mχ , m2 > mh =2. The upper bound on σ SI arises from the requirement the HS vacuum be global, which bound is stronger than that from unitarity that also con- strains the points from above. In Fig. 2, we present the predicted stochastic GW signal together with the predicted sensitivity curves of the future LISA and the BBO satellite experiments. We used bubble wall velocity vw ¼ 0.5 and the fraction κ turb ¼ 0.05κ v in a turbulent motion that is converted into gravitational waves following [96], where the fraction κ v of vacuum energy converted into gravitational waves is given in [100]. To avoid cluttering the plot, we only show the peak power of each GW spectrum. In the left panel, light red points are excluded by the XENON1T direct detection constraints, while the darker green points are still allowed by direct detection; all points not satisfying the other constraints have been excluded. In the right panel, we depict the dependence of the GW signal on the cubic coupling μ3 . The color code shows the nature of the phase transition that yields the strongest signal in a sequence of phase transitions. The largest signal is produced by the O → S transitions, enhanced by a sizable cubic coupling. Because mχ ∝ μ3 , there is a similar dependence on mχ =m2 . The strongest signals can be produced at roughly mχ ≈ 2.3m2. In the left panel of Fig. 3, we show the correlation FIG. 3. Left panel: Scatter plot for the peak power of GWs vs direct detection cross section. The points pass all other con- between the gravitational wave signal and the direct straints. Right panel: Signal-to-noise ratios of the data points for detection cross section. the BBO experiment. Light red points are forbidden and darker We have also calculated the signal-to-noise ratio for the green points are allowed by the results of the XENON1T direct BBO experiment, shown in the right panel of Fig. 3 with the detection searches; both sets of points pass all other constraints. same color code as Fig. 1. The horizontal thick line shows The horizontal thick line shows SNR ¼ 1. 035001-5
KANNIKE, LOOS, and RAIDAL PHYS. REV. D 101, 035001 (2020) ACKNOWLEDGMENTS We would like to thank Matti Heikinheimo and Christian Gross for useful comments. This work was supported by the Estonian Research Council Grant No. PRG434, the Grant No. IUT23-6 of the Estonian Ministry of Education and Research, and by the European Union through the ERDF Centre of Excellence program Project No. TK133. APPENDIX: THERMAL EFFECTIVE POTENTIAL At the one-loop level, the quantum corrections to the scalar potential in the MS renormalization scheme are given by X 1 FIG. 4. β=H vs α. Light red points are forbidden and darker 4 m2i green points are allowed by the results of the XENON1T direct ΔV ¼ ni mi ln 2 − ci ; ðA1Þ i 64π 2 μ detection searches. where ni are the d.o.f. of the ith field, mi are field- SNR ¼ 1; the actual detection threshold is expected to be dependent masses, and the constants ci ¼ 32 for scalars within an order of magnitude of it [96]. and fermions and ci ¼ 56 for vector bosons. The masses and Because the direct detection cross section is proportional d.o.f. ni of the fields are given in Table I. The field- to μ23 , the points on the left panel of Fig. 2 with the highest dependent masses of h and s are given by the eigenvalues GW signal are excluded. Note, however, that the direct m21;2 of the mass matrix of the CP-even eigenstates with detection signal can still be small even for a sizeable GW elements given by signal, because the Higgs portal λSH is on the order of (0.01). This is in contrast with λSH ∼ 1 in Ref. [74] with the 1 ðm2R Þ11 ¼ μ2H þ 3h2 λH þ λSH s2 ; ðA2Þ assumption that the Z3 symmetry is unbroken in our vacuum. 2 Figure 4 shows the range of β=H vs α with the same 2 ðmR Þ12 ¼ λSH hs; ðA3Þ color code as Fig. 1. While Ref. [101] showed that for α close to unity the gravitational wave signal is suppressed, 3 pffiffiffi 1 ðm2R Þ22 ¼ μ2S þ 3λS s2 þ 2μ3 s þ h2 λSH : ðA4Þ our values of α are quite smaller than one. 2 2 We neglect the contributions of the Goldstone bosons G0 V. CONCLUSIONS and G as unimportant numerically. To calculate the We have studied the Z3 complex scalar singlet DM effective potential in the case of negative field-dependent model, where only the cubic coupling of the singlet masses, we substitute ln m2i → ln jm2i j, which is equivalent explicitly breaks a global Uð1Þ symmetry. The model to analytical continuation [102]. We set the renormalization has two phases with stable DM. In the phase where the scale to μ ¼ M t . Z3 is spontaneously broken, the residual CP-like Z2 We add a counterterm potential, symmetry stabilizes the imaginary part of the complex singlet S as a pseudo-Goldstone DM candidate. The DM δV ¼ δμ2H jHj2 þ δλH jHj4 þ δμ2S jSj2 þ δλS jSj4 direct detection cross section can be considerably sup- δμ3 3 pressed by the small momentum transfer or the resonance at þ δλSH jSj2 jHj2 þ ðS þ S†3 Þ þ δV 0 ; ðA5Þ half the mass of the heavy singletlike particle. 2 While we may be unable to discover the pseudo- Goldstone DM via direct detection, it may be testable by TABLE I. Field-dependent masses and the numbers of d.o.f. other means. In this model, a stochastic gravitational wave background can arise from the first-order phase transitions Field i m2i ni due to the presence of a cubic coupling for the singlet. The h m21 1 strongest signals, which can potentially be observed by the s m22 1 future BBO experiment, are produced in the O → S phase χ μS þ λS s − 3ffiffi2 μ3 s þ 12 λSH h2 2 2 p 1 transition (if present) at mχ ≈ 2.3m2 . The strength of the Z0 1 2 02 2 4 ðg þ g Þh 3 gravitational wave signal is anticorrelated with a small W 1 2 2 6 4g h mixing angle and is, therefore, greater where the direct t 1 2 −12 2 yt h detection cross section is smaller (at fixed cubic coupling). 035001-6
GRAVITATIONAL WAVE SIGNALS OF PSEUDO-GOLDSTONE … PHYS. REV. D 101, 035001 (2020) in order to fix the VEVs and the mass matrix in our HS The counterterm potential δV is chosen such as to keep minimum to their tree-level values. quantum corrections to the masses, to mixing between h The thermal corrections to the potential are given by and s and to the VEVs zero. The counterterms are given by T4 X mi 1 VT ¼ 2 ni J ∓ ; ðA6Þ δλH ¼ ð∂ h ΔV − v∂ 2h ΔVÞ; ðA10Þ 2π i T 2v3 1 δλS ¼ ð4∂ s ΔV − vS ∂ 2χ ΔV − 3vS ∂ 2s ΔVÞ; ðA11Þ where 6v3S Z ∞ h qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi i 1 J∓ ¼ dyy2 ln 1 ∓ exp − y2 þ x2 ; ðA7Þ δλSH ¼ − ∂ ∂ ΔV; ðA12Þ vvS h s 0 1 with the − sign applied to bosons and the þ sign to δμ2H ¼ ð−3∂ h ΔV þ vs ∂ h ∂ s ΔV þ v∂ 2h ΔVÞ; ðA13Þ 2v fermions. In the high-temperature limit m=T ≪ 1, the 1 thermal contributions are given by δμ2S ¼ − ðv ∂ 2 ΔV þ 8∂ s ΔV − 3vS ∂ 2s ΔV 6vS S χ T2 X − 3v∂ h ∂ s ΔVÞ; ðA14Þ V T ðTÞ ¼ n m2 : ðA8Þ 24 i i i pffiffiffi 2 2 δμ3 ¼ 2 ðvS ∂ 2χ ΔV − ∂ s ΔVÞ; ðA15Þ The full thermally corrected effective potential is then 9vS where we take h ¼ v, s ¼ vS , χ ¼ 0 after taking the V ð1Þ ¼ V þ ΔV þ δV þ V T : ðA9Þ derivatives. [1] V. Silveira and A. Zee, Scalar phantoms, Phys. Lett. B 161, [12] C. Gross, O. Lebedev, and T. Toma, Cancellation Mecha- 136 (1985). nism for Dark-Matter–Nucleon Interaction, Phys. Rev. [2] J. McDonald, Gauge singlet scalars as cold dark matter, Lett. 119, 191801 (2017). Phys. Rev. D 50, 3637 (1994). [13] C.-W. Chiang, M. J. Ramsey-Musolf, and E. Senaha, [3] V. Barger, P. Langacker, M. McCaskey, M. Ramsey- Standard Model with a complex scalar singlet: Cosmo- Musolf, and G. Shaughnessy, Complex singlet extension logical implications and theoretical considerations, Phys. of the Standard Model, Phys. Rev. D 79, 015018 (2009). Rev. D 97, 015005 (2018). [4] C. P. Burgess, M. Pospelov, and T. ter Veldhuis, The [14] D. Azevedo, M. Duch, B. Grzadkowski, D. Huang, M. minimal model of nonbaryonic dark matter: A singlet Iglicki, and R. Santos, One-loop contribution to dark scalar, Nucl. Phys. B619, 709 (2001). matter-nucleon scattering in the pseudoscalar dark matter [5] J. M. Cline, K. Kainulainen, P. Scott, and C. Weniger, model, J. High Energy Phys. 01 (2019) 138. Update on scalar singlet dark matter, Phys. Rev. D 88, [15] K. Ishiwata and T. Toma, Probing pseudo Nambu- 055025 (2013); Erratum, Phys. Rev. D 92, 039906 (2015). Goldstone boson dark matter at loop level, J. High Energy [6] A. Djouadi, O. Lebedev, Y. Mambrini, and J. Quevillon, Phys. 12 (2018) 089. Implications of LHC searches for Higgs–portal dark [16] K. Huitu, N. Koivunen, O. Lebedev, S. Mondal, and T. matter, Phys. Lett. B 709, 65 (2012). Toma, Probing pseudo-Goldstone dark matter at the LHC, [7] P. Athron et al., Status of the scalar singlet dark matter Phys. Rev. D 100, 015009 (2019). model, Eur. Phys. J. C 77, 568 (2017). [17] T. Alanne, M. Heikinheimo, V. Keus, N. Koivunen, and [8] G. Arcadi, A. Djouadi, and M. Raidal, Dark matter through K. Tuominen, Direct and indirect probes of Goldstone dark the Higgs portal, arXiv:1903.03616. matter, Phys. Rev. D 99, 075028 (2019). [9] D. S. Akerib et al., Results from a Search for Dark Matter [18] D. Azevedo, M. Duch, B. Grzadkowski, D. Huang, M. in the Complete LUX Exposure, Phys. Rev. Lett. 118, Iglicki, and R. Santos, Testing scalar versus vector dark 021303 (2017). matter, Phys. Rev. D 99, 015017 (2019). [10] E. Aprile et al., Dark Matter Search Results from a One [19] J. M. Cline and T. Toma, Pseudo-Goldstone dark matter Ton-Year Exposure of XENON1T, Phys. Rev. Lett. 121, confronts cosmic ray and collider anomalies, Phys. Rev. D 111302 (2018). 100, 035023 (2019). [11] X. Cui et al., Dark Matter Results from 54-Ton-Day [20] X.-M. Jiang, C. Cai, Z.-H. Yu, Y.-P. Zeng, and H.-H. Exposure of PandaX-II Experiment, Phys. Rev. Lett. Zhang, Pseudo-Nambu-Goldstone dark matter and two 119, 181302 (2017). Higgs doublets, Phys. Rev. D 100, 075011 (2019). 035001-7
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