[Paper Review] The Higgs Portal and Cosmology

K. Assamagan, Chien-Yi Chen+20 more|arXiv (Cornell University)|Apr 18, 2016

Particle physics theoretical and experimental studies4 citations

TL;DR

This paper proposes that Higgs portal interactions—couplings between the Standard Model Higgs boson and new physics—offer a unified framework for addressing two major cosmological puzzles: dark matter relic abundance and baryon asymmetry via electroweak baryogenesis. It demonstrates that such portals can enable a strong first-order electroweak phase transition and CP violation, while also supporting viable dark matter candidates, with detectable signatures at the LHC and future colliders like FCC-hh and ILC.

ABSTRACT

Higgs portal interactions provide a simple mechanism for addressing two open problems in cosmology: dark matter and the baryon asymmetry. In the latter instance, Higgs portal interactions may contain the ingredients for a strong first order electroweak phase transition as well as new CP-violating interactions as needed for electroweak baryogenesis. These interactions may also allow for a viable dark matter candidate. We survey the opportunities for probing the Higgs portal as it relates to these questions in cosmology at the LHC and possible future colliders.

Motivation & Objective

• To investigate how Higgs portal interactions can simultaneously address the dark matter relic density and the origin of the baryon asymmetry in the universe.
• To identify viable theoretical models—such as real singlets and complex triplets—where Higgs portal couplings generate a strong first-order electroweak phase transition and CP violation.
• To map out detectable collider signatures at the LHC and future colliders (e.g., ILC, FCC, CEPC) for these cosmologically motivated scenarios.
• To assess the potential of future high-energy colliders to probe the Higgs portal’s role in electroweak baryogenesis and dark matter production.
• To guide experimental searches by identifying key observables such as modified Higgs self-couplings, invisible Higgs decays, and exotic Higgs decay channels.

Proposed method

• Analyzes effective field theory models with Higgs portal couplings to scalar singlets and complex triplets, focusing on their impact on the electroweak phase transition and CP violation.
• Applies constraints from cosmological observations, including the baryon-to-photon ratio $Y_B = (8.59 \pm 0.11) \times 10^{-11}$, to narrow viable parameter space.
• Evaluates collider signatures such as invisible Higgs decays ($h \to \chi\chi$), modified Higgs self-couplings, and exotic decays like $h_2 \to h_1 h_1 \to b\bar{b}\tau^+\tau^-$, $b\bar{b}\gamma\gamma$, and $b\bar{b}b\bar{b}$.
• Assesses the discovery potential of these signatures at the 14 TeV LHC with 100 fb⁻¹ luminosity, particularly for triplet models with $H^+H^0_2 \to b\bar{b}\tau\nu$.
• Considers future collider capabilities at ILC, FCC-ee, CEPC, and SppC/FCC-hh for precision measurements of Higgs self-couplings and signal reductions.
• Uses theoretical consistency conditions such as unitarity, vacuum stability, and perturbativity to constrain model parameters.

Experimental results

Research questions

• RQ1 Can Higgs portal interactions generate a strong first-order electroweak phase transition necessary for electroweak baryogenesis?
• RQ2 What are the detectable collider signatures of Higgs portal models that simultaneously explain dark matter and baryon asymmetry?
• RQ3 How can future colliders like FCC-hh and ILC probe the Higgs portal’s role in electroweak baryogenesis and dark matter relic density?
• RQ4 What constraints do the observed baryon-to-photon ratio and dark matter abundance place on Higgs portal coupling strengths and scalar masses?
• RQ5 Can exotic Higgs decays such as $h_2 \to h_1 h_1 \to b\bar{b}\tau^+\tau^-$ be observed at the LHC with 100 fb⁻¹ of data?

Key findings

• Higgs portal interactions with a real singlet scalar can lead to a strong first-order electroweak phase transition and modified Higgs self-couplings, with detectable signal reductions at the LHC and future colliders.
• For the real singlet model, a discovery via signal reduction in Higgs production is possible at the LHC with 100 fb⁻¹, and modified self-couplings can be probed at ILC, FCC-ee, and CEPC.
• In the real triplet model, a strong first-order phase transition and CP violation are possible, with signatures including disappearing charged tracks and reduced $\Gamma(h \to \gamma\gamma)$, detectable at the LHC.
• The $H^+H^0_2 \to b\bar{b}\tau\nu$ channel in the triplet model may be observable at the 14 TeV LHC with 100 fb⁻¹, depending on the sign and magnitude of the portal coupling $a_2$.
• Exotic decay chains such as $h_2 \to h_1 h_1 \to b\bar{b}\tau^+\tau^-$, $b\bar{b}\gamma\gamma$, and $b\bar{b}b\bar{b}$ are viable search channels at the LHC, with potential discovery significance depending on model parameters.
• Future colliders like FCC-hh and SppC offer enhanced sensitivity to invisible Higgs decays and modified self-couplings, particularly for models not saturating the dark matter relic density.