First-order Electroweak Phase Transition Research Articles

Electroweak phase transition in two scalar singlet model with pNGB dark matter

We investigate the dynamics of the electroweak phase transition within an extended Standard Model framework that includes one real scalar (Φ) and one complex scalar (S), both of which are SM gauge singlets. The global U(1) symmetry is softly broken to a Z3 symmetry by the S3 term in the scalar potential. After this U(1) symmetry breaking, the imaginary component of the complex scalar (S) acts as a pseudo-Nambu-Goldstone boson (pNGB) dark matter candidate, naturally stabilized by the Z2 symmetry of the scenario. Specially, the spontaneous breaking of the global U(1) symmetry to a discrete Z3 subgroup can introduce effective cubic terms in the scalar potential, which facilitates a strong first-order phase transition. We analyze both single-step and multi-step first-order phase transitions, identifying the parameter space that satisfies the dark matter relic density constraints, complies with all relevant experimental constraints, and exhibits a strong first-order electroweak phase transition. The interplay of these criteria significantly restricts the model parameter space, often leading to an underabundant relic density. Moreover, we delve into the gravitational wave signatures associated with this framework, offering valuable insights that complement traditional dark matter direct and indirect detection methods.

Effective field theory for a singlet scalar extension of the standard model and electroweak phase transition

In this paper, we study an effective field theory (EFT) for a singlet scalar extension of the standard model (SM). The tree- and one-loop level effective actions are derived by integrating out the heavy singlet scalar in the Lagrangian for the UV theory and by applying to the functional method, respectively. In the UV model, the light scalar field identified with the SM Higgs is assumed to be massless in the symmetric phase. When the heavy singlet scalar acquires a vacuum expectation value, the [Formula: see text] symmetry is broken and a mass term of the light scalar is induced. In light of EFT we derive, the electroweak vacuum resulting in 126[Formula: see text]GeV Higgs mass can be attained when the induced squared-mass term of the light scalar in the scalar potential becomes negative. This condition can occur when the constant of the scalar coupling between the two different scalars is allowed to be negative. We investigate how the EFT can be constrained by theory and experiments. We also examine whether or not electroweak phase transition (EWPT) in this scenario can be a first order. Some numerical results leading to the first-order EWPT while satisfying the constraints studied are presented.

Gravitational waves from thermal heavy scalar dark matter

We propose a gauge singlet scalar with mass around 1–100 TeV as a thermal heavy dark matter candidate along with a dilaton as a Higgs portal mediator in a dimensionless scalar extension of the Standard Model. We demonstrate analytically that such a model gives rise to very strong first-order electroweak phase transition through supercooling. We calculate the corresponding gravitational wave signals due to bubble collisions during the phase transition. The produced gravitational waves can be detected by future space-based gravitational wave detectors in the frequency range from 10−4 to 0.1 Hz. Published by the American Physical Society 2024

Double and triple Higgs boson production to probe the electroweak phase transition

The production of three Higgs bosons could be a stretch goal for the LHC and a strategic case for future colliders. In this work, we analyse the phenomenological prospects of (neutral) triple Higgs compared to di-Higgs boson production, for a range of Higgs-sector extensions from a strong first-order electroweak phase transition perspective. In parallel, we include constraints from existing exotics and Higgs boson measurements that further limit the parameter space of such models. Resonance contributions offer large modifications in particular for triple Higgs production, albeit starting from a small SM expectation. With enhancements of order 40 over the SM, however, experimental efforts to obtain limits at the HL-LHC are well motivated and well placed. This is further highlighted by the potential of these processes to inform the investigation of the thermal history of our Universe. Published by the American Physical Society 2024

Thermal pressure on ultrarelativistic bubbles from a semiclassical formalism

We study a planar bubble wall that istravelingat an ultrarelativistic speed through a thermal plasma. This situation may arise during a first-order electroweak phase transition in the early universe. As particles cross the wall, it is assumed that their mass grows from m a to m b , and they are decelerated causing them to emit massless radiation (m c = 0). We are interested in the momentum transfer to the wall, the thermal pressure felt by the wall, and the resultant terminal velocity of the wall. We employ the semiclassical current radiation (SCR) formalism to perform these calculations. An incident-charged particle is treated as a point-like classical electromagnetic current, and the spectrum of quantum electromagnetic radiation (photons) is derived by calculating appropriate matrix elements. To understand how the spectrum depends on the thickness of the wall, we explore simplified models for the current corresponding to an abrupt and a gradual deceleration. For the model of abrupt deceleration, we find that the SCR formalism can reproduce the P therm ∝ γ 0 w scaling found in earlier work by assuming that the emission is soft, but if the emission is not soft the SCR formalism can be used to obtain P therm ∝ γ 2 w instead. For the model of gradual deceleration, we find that the wall thickness L w enters to cutoff the otherwise log-flat radiation spectrum above a momentum of ∼ γ 2 w / L w , and we discuss the connections with classical electromagnetic bremsstrahlung.

A complex singlet extension of the Standard Model with a singlet fermion dark matter

We examine a complex singlet scalar extension of the Standard Model (CxSM) with an extra singlet fermion. Both the singlet scalar and fermion are dark matter (DM) candidates. It is known that although the scalar potential in the CxSM can realize strong first-order electroweak phase transition, the scalar DM included in the model gives only a tiny amount of the relic density compared to the observed one. Therefore, a fermion DM is introduced to compensate for the lack of relic density. We find that the scattering of the fermion DM and nucleons is sufficiently suppressed when the masses of scalar mediators are degenerate, as is the case of the scalar DM. We show the range of a combination of the mass and the Yukawa coupling of the fermion DM, which satisfies both the observed relic density and conditions of strong first-order electroweak phase transition.

Probing electroweak phase transition in extended singlet scalar model with resonant HH production in bbZZ channel using parameterized machine learning

In this paper, a collider signature of a heavy Higgs boson at 14 TeV HL-LHC is studied, where the heavy Higgs boson decays into a pair of standard model (SM) Higgs boson, which further decays to bbZZ state and subsequently to bb ℓ + ℓ − ν ℓ ν ℓ final state. To study this, we consider singlet scalar extension of the SM and select the parameter space and mass of the heavy Higgs boson such that it prefers a strong first-order electroweak phase transition (EWPT). The study is done following the bbZZ analysis of CMS Collaboration and further using parameterized machine learning for final discrimination which simplifies the training process along with an improved discrimination between signal and background over the range of benchmark points. Despite the lower branching fraction, this channel can be a potential probe of the EWPT with the data sets collected by the CMS and ATLAS experiments at the 14 TeV HL-LHC with 3 ab−1 of integrated luminosity and a production of resonant di-Higgs signal can be potentially discovered up to 490 GeV of resonance mass.

First-order electroweak phase transition at finite density

We study the Electroweak phase transition with the Standard Model effective field theory at finite temperature and finite density. Utilizing the dimensional reduction approach, we construct the tree dimensional thermal effective field theory at finite density and investigate the phase transition dynamics. We evaluate how the results depend on the renormalization scale and the chemical potential. Our results show that, with the tree dimensional thermal effective potential at 2-loop level, we can effectively reduce the theoretical uncertainty in the calculations of the phase transition parameters due to the renormalization scale dependence, and the new physics scale is restricted to be Λ ≲ (770 − 800) GeV by the baryon number washout avoidance condition. Meanwhile, the presence of the chemical potential would affect the phase transition parameter and make the constraints from the baryon number washout avoidance condition more strict, especially for weaker first-order phase transition scenarios at higher new physics scales.

Gravitational wave effects and phenomenology of a two-component dark matter model

We study an extension of the Standard Model (SM) which could have two candidates for dark matter (DM) including a Dirac fermion and a vector dark matter (VDM) under a new U(1) gauge group in the hidden sector. The model is classically scale-invariant and the electroweak symmetry breaks because of loop effects. We investigate the parameter space allowed by current experimental constraints and phenomenological bounds. We probe the parameter space of the model in the mass range 1<MV<5000\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1< M_V<5000$$\\end{document} GeV and 1<Mψ<5000\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1<M_{\\psi }<5000$$\\end{document} GeV. It has been shown that there are many points in this mass range that are in agreement with all phenomenological constraints. The electroweak phase transition has been discussed and it has been shown that there is region in the parameter space of the model consistent with DM relic density and direct detection constraints that, at the same time, can lead to first-order electroweak phase transition. The gravitational waves produced during the phase transition could be probed by future space-based interferometers such as LISA and BBO.

ALP-assisted strong first-order electroweak phase transition and baryogenesis

Axion-like particles (ALPs) can be naturally lighter than the electroweak scale. We consider an ALP that couples to the Standard Model Higgs to achieve the strong first-order electroweak phase transition. We discuss the two-field dynamics of the phase transition and the associated computation in detail and identify the viable parameter space. The ALP mass can be from the MeV to GeV scale. Baryon asymmetry can be explained by local baryogenesis without violating the current electron and atom electric dipole moment bound in most of the viable parameter space. The viable parameter space can be probed through Higgs exotic decay, rare kaon decay, the electron and atomic electric dipole moment, and the effective number of neutrinos in the cosmic microwave background in the future. The gravitational-wave signal is too weak to be detected.

Electroweak baryogenesis, dark matter, and dark CP symmetry

With the motivation of explaining the dark matter and achieving the electroweak baryogenesis via the spontaneous CP violation at high temperature, we propose a complex singlet scalar (S=χ+iηs2) extension of the two-Higgs-doublet model respecting a discrete dark CP symmetry: S→−S*. The dark CP symmetry guarantees χ to be a dark matter candidate on one hand and on the other hand allows ηs to have mixings with the pseudoscalars of the Higgs doublet fields, which play key roles in generating the CP violation sources needed by the electroweak baryogenesis at high temperature. The Universe undergoes multistep phase transitions, including a strongly first-order electroweak phase transition during which the baryon number is produced. At the present temperature, the observed vacuum is produced and the CP symmetry is restored so that the stringent electric dipole moment experimental bounds are satisfied. Considering relevant constraints, we study the simple scenario of mχ around the Higgs resonance region, and find that the dark matter relic abundance and the baryon asymmetry can be simultaneously explained. Finally, we briefly discuss the gravitational wave signatures at future space-based detectors and the LHC signatures. Published by the American Physical Society 2024

Effective 2HDM Yukawa interactions and a strong first-order electroweak phase transition

The top quark as the heaviest particle in the Standard Model (SM) defines an important mass scale for Higgs physics and the electroweak scale itself. It is therefore a well-motivated degree of freedom which could reveal the presence of new interactions beyond the SM. Correlating modifications of the top-Higgs interactions in the 2-Higgs-Doublet Model (2HDM), we analyse effective field theory deformations of these interactions from the point of view of a strong first-order electroweak phase transition (SFOEWPT). We show that such modifications are compatible with current Higgs data and that an SFOEWPT can be tantamount to a current overestimate of exotic Higgs searches’ sensitivity at the LHC in tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document} and four top quark final states. We argue that these searches remain robust from the point of accidental signal-background interference so that the current experimental strategy might well lead to 2HDM-like discoveries in the near future.

Primordial magnetogenesis in the two-Higgs-doublet model

γ-ray emission of blazars infer the presence of large-scale magnetic fields in the intergalactic medium, but their origin remains a mystery. Using recent data from MAGIC, H.E.S.S., and Fermi-LAT, we investigate whether the large-scale magnetic fields in the intergalactic medium could have been generated by a first-order electroweak phase transition in the two-Higgs-doublet model (2HDM). We study two representative scenarios where we vary the initial conditions of the magnetic field and the plasma, assuming either a primordial magnetic field with maximal magnetic helicity or a primordial magnetic field with negligible magnetic helicity in a plasma with kinetic helicity. By considering a primordial magnetic field with maximal helicity and applying the conservative constraints derived from MAGIC and Fermi-LAT data, we demonstrate that a first-order electroweak phase transition within the 2HDM may account for the observed intergalactic magnetic fields in the case of the strongest transitions. We show that this parameter space also predicts strong gravitational wave signals in the reach of space-based detectors such as LISA, providing a striking multimessenger signal of the 2HDM. Published by the American Physical Society 2024

First shot of the smoking gun: probing the electroweak phase transition in the 2HDM with novel searches for A → ZH in ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} and ννbb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \ u b\\overline{b} $$\\end{document} final states

Recently the ATLAS collaboration has reported the first results of searches for heavy scalar resonances decaying into a Z boson and a lighter new scalar resonance, where the Z boson decays leptonically and the lighter scalar decays into a top-quark pair, giving rise to ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} final states. This had previously been identified as a smoking-gun signature at the LHC for a first-order electroweak phase transition (FOEWPT) within the framework of two Higgs doublet models (2HDMs). In addition, ATLAS also presented new limits where the Z boson decays into pairs of neutrinos and the lighter scalar resonance into bottom-quark pairs, giving rise to the ννbb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \ u b\\overline{b} $$\\end{document} final state. We analyze the impact of these new searches on the 2HDM parameter space, with emphasis on their capability to probe currently allowed 2HDM regions featuring a strong FOEWPT. We also study the complementarity of these new searches with other LHC probes that could target the FOEWPT region of the 2HDM. Remarkably, the ATLAS search in the ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} final state shows a local 2.85 σ excess (for masses of about 650 GeV and 450 GeV for the heavy and light resonance) in the 2HDM parameter region that would yield a FOEWPT in the early universe, which could constitute the first experimental hint of baryogenesis at the electroweak scale. We analyze the implications of this excess, and discuss the detectability prospects for the associated gravitational wave signal from the FOEWPT. Furthermore, we project the sensitivity reach of the ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} signature for the upcoming runs of the LHC. Finally, we introduce the python package thdmTools, a state-of-art tool for the exploration of the 2HDM.

Interplay among gravitational waves, dark matter and collider signals in the singlet scalar extended type-II seesaw model

We study the prospect of simultaneous explanation of tiny neutrino masses, dark matter (DM), and the observed baryon asymmetry of the Universe in a Z3-symmetric complex singlet scalar extended type-II seesaw model. The complex singlet scalar plays the role of DM. Analyzing the thermal history of the model, we identify the region of the parameter space that can generate a first-order electroweak phase transition (FOEWPT) in the early Universe, and the resulting stochastic gravitational waves (GW) can be detected at future space/ground-based GW experiments. First, we find that light triplet scalars do favor an FOEWPT. In our study, we choose the type-II seesaw part of the parameter space in such a way that light triplet scalars, especially the doubly charged ones, evade the strong bounds from their canonical searches at the Large Hadron Collider (LHC). However, the relevant part of the parameter space, where FOEWPT can happen only due to strong SM doublet-triplet interactions, is in tension with the SM-like Higgs decay to a pair of photons, which has already excluded the bulk of this parameter space. On the other hand, the latest spin-independent DM direct detection constraints from XENON-1T and PANDA-4T eliminate a significant amount of parameter space relevant for the dark sector assisted FOEWPT scenarios, and it is only possible when the complex scalar DM is significantly underabundant. In short, we conclude from our analysis that the absence of new physics at the HL-LHC and/or various DM experiments in the near future will severely limit the prospects of detecting a stochastic GW at future GW experiments and will exclude the possibility of electroweak baryogenesis within this model.

Correction to: 'Gravitational waves from a first-order electroweak phase transition: a brief review' (2018) by Weir.

Correction to: 'Gravitational waves from a first-order electroweak phase transition: a brief review' (2018) by Weir.

Electroweak phase transition and gravitational wave: Higgs potential from 10−11 s of early universe to 2022

After the discovery of the Higgs boson, the 125 GeV scalar boson becomes a realistic portal to study the fundamental physics and its deep connections to cosmology. The true shape of the Higgs potential becomes essential to the dynamics of the electroweak spontaneous symmetry breaking, the electroweak baryogenesis, Higgs portal dark matter, and the phase transition gravitational wave (GW). Especially, the GW from first-order electroweak phase transition provides new and realistic approaches to explore the Higgs potential and its abundant cosmological effects. Meanwhile, Precise calculations of the phase transition dynamics and the GW spectra are crucial to experimental signals.

Type-II seesaw Complex Triplet Model: Phase Transition and Global Fit Analysis

The type-II seesaw model can explain neutrino masses and address the baryon asymmetry problem of the Universe simultaneously. In this letter, we explore its phase transition and the resulting gravitational wave signals. We find a strong first-order electroweak phase transition generically prefers a relatively light triplet in the 300∼500GeV range, which is ideal for collider searches and can generate gravitational waves within the sensitivity reach of BBO and Ultimate-DECIGO. While above ∼1TeV where a future 100 TeV pp collider will play a key role in model discovery, we integrate out the triplet and perform a global fit analysis of this model at various future colliders. A lower bound in the 10−3∼10−2eV range on the triplet vacuum expectation value is obtained, which is comparable or even better than that from current μ→eγ experiments depending on the first generation neutrino mass.

SMEFT effects on the gravitational wave spectrum from an electroweak phase transition

Future gravitational wave observations are potentially sensitive to new physics corrections to the Higgs potential once the first-order electroweak phase transition arises. We study the SMEFT dimension-six operator effects on the Higgs potential, where three types of effects are taken into account: (i) SMEFT tree level effect on $\varphi^6$ operator, (ii) SMEFT tree level effect on the wave function renormalization of the Higgs field, and (iii) SMEFT top-quark one-loop level effect. The sensitivity of future gravitational wave observations to these effects is numerically calculated by performing a Fisher matrix analysis. We find that the future gravitational wave observations can be sensitive to (ii) and (iii) once the first-order electroweak phase transition arises from (i). The dimension-eight $\varphi^8$ operator effects on the first-order electroweak phase transition are also discussed. The sensitivities of the future gravitational wave observations are also compared with those of future collider experiments.

Gravitational wave signals from leptoquark-induced first-order electroweak phase transitions

We consider the extension of the Standard Model (SM) with scalar leptoquarks in SU(2) singlet, doublet and triplet representations. Through the coupling between leptoquark and the SM Higgs field, the electroweak phase transition (EWPT) can turn into first-order and consequently produce gravitational wave signals. We compute the required value of the leptoquark-Higgs for first-order EWPT to happen and discuss about the possible constraint from Higgs phenomenology. Choosing some benchmarks, we present the strength of the gravitational waves produced during the leptoquark-induced first-order EWPT and compare them to detector sensitivities. We find that the SU(2) representations of the leptoquark can be distinguished by gravitational waves in the parameter space where first-order EWPT can happen as a function of the Higgs portal coupling.