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A unified explanation for dark matter and electroweak baryogenesis with direct detection and gravitational wave signatures

Mikael Chala, Germano Nardini, Ivan Sobolev

TL;DR

This work presents a non-minimal composite Higgs model based on the SO(7)/SO(6) coset, featuring two SM-singlet pNGBs, eta and kappa. Eta acts as a stable dark matter candidate, while kappa induces a strongly first-order electroweak phase transition with CP-violating effects, enabling electroweak baryogenesis within a predictive three-parameter setup (f, mu_kappa^2, lambda_hkappa). The model yields DM relic density with m_eta ≈ 0.7–1 TeV and f ≈ 2.4–2.9 TeV, and a two-step EWPT with v1(T_n)/T_n > 1 in viable regions, accompanied by gravitational wave signals potentially detectable by eLISA. Current experimental constraints are satisfied, and the scenario makes clear, testable predictions for future direct-detection experiments and gravitational-wave observations, offering a cohesive path to solving DM and baryogenesis.

Abstract

A minimal extension of the Standard Model that provides both a dark matter candidate and a strong first-order electroweak phase transition (EWPT) consists of two additional Lorentz and gauge singlets. In this paper we work out a composite Higgs version of this scenario, based on the coset $SO(7)/SO(6)$. We show that by embedding the elementary fermions in appropriate representations of $SO(7)$, all dominant interactions are described by only three free effective parameters. Within the model dependencies of the embedding, the theory predicts one of the singlets to be stable and responsible for the observed dark matter abundance. At the same time, the second singlet introduces new $CP$-violation phases and triggers a strong first-order EWPT, making electroweak baryogenesis feasible. It turns out that this scenario does not conflict with current observations and it is promising for solving the dark matter and baryon asymmetry puzzles. The tight predictions of the model will be accessible at the forthcoming dark matter direct detection and gravitational wave experiments.

A unified explanation for dark matter and electroweak baryogenesis with direct detection and gravitational wave signatures

TL;DR

This work presents a non-minimal composite Higgs model based on the SO(7)/SO(6) coset, featuring two SM-singlet pNGBs, eta and kappa. Eta acts as a stable dark matter candidate, while kappa induces a strongly first-order electroweak phase transition with CP-violating effects, enabling electroweak baryogenesis within a predictive three-parameter setup (f, mu_kappa^2, lambda_hkappa). The model yields DM relic density with m_eta ≈ 0.7–1 TeV and f ≈ 2.4–2.9 TeV, and a two-step EWPT with v1(T_n)/T_n > 1 in viable regions, accompanied by gravitational wave signals potentially detectable by eLISA. Current experimental constraints are satisfied, and the scenario makes clear, testable predictions for future direct-detection experiments and gravitational-wave observations, offering a cohesive path to solving DM and baryogenesis.

Abstract

A minimal extension of the Standard Model that provides both a dark matter candidate and a strong first-order electroweak phase transition (EWPT) consists of two additional Lorentz and gauge singlets. In this paper we work out a composite Higgs version of this scenario, based on the coset . We show that by embedding the elementary fermions in appropriate representations of , all dominant interactions are described by only three free effective parameters. Within the model dependencies of the embedding, the theory predicts one of the singlets to be stable and responsible for the observed dark matter abundance. At the same time, the second singlet introduces new -violation phases and triggers a strong first-order EWPT, making electroweak baryogenesis feasible. It turns out that this scenario does not conflict with current observations and it is promising for solving the dark matter and baryon asymmetry puzzles. The tight predictions of the model will be accessible at the forthcoming dark matter direct detection and gravitational wave experiments.

Paper Structure

This paper contains 7 sections, 39 equations, 5 figures.

Table of Contents

  1. Introduction
  2. A quick look at composite models
  3. Model description
  4. Dark matter predictions
  5. Electroweak baryogenesis
  6. Other constraints and future expectations
  7. Conclusions

Figures (5)

  • Figure 1: Main diagrams contributing to the DM annihilation. The double dashed lines stand for $\eta$. In the first plot the solid legs account for either SM particles or $\kappa$. In the second diagram the simple dashed lines represent either the Higgs boson or $\kappa$. In the third diagram the fermion lines stand for (mainly) the top quark. In the fourth diagram the simple dashed lines represent the Higgs boson.
  • Figure 2: Value of $f$ leading to $\Omega_\eta = \Omega_{\rm DM}$ as a function of $\lambda_{h\kappa}$ in Regime I (dashed blue) and Regime II (solid green). The masses $m_\eta$ corresponding to two extreme points are also depicted.
  • Figure 3: Points of the parameter space exhibiting a strong EWPT in Regime I (left panel) and Regime II (right panel). The region in green indicates the points for which $V_{\rm 1L}(h,\kappa; T\!=\!0)$ has a local minimum at $v_1$ (the contrary in the white area) and such a minimum is deeper than the one at $v_2$ (the contrary in the orange area). The points on the left of the black dashed line are unfavored by the Higgs searches. The filled (empty) circles correspond to EWPTs with bubbles expanding (not expanding) at the speed of light.
  • Figure 4: Main diagrams contributing to the scattering of DM particles by nuclei.
  • Figure 5: The identified first-order EWPTs with non-runaway (left panel) and runaway (right panel) behavior in the $\{\alpha,\beta/H\}$ plane. Black circles and red squares represent the EWPTs of Regime I and Regime II, respectively. eLISA in the N2A5M5L6 experimental design can test the EWPTs inside the green areas.