[Paper Review] Reconciling Higgs physics and pseudo-Nambu-Goldstone dark matter in the S2HDM using a genetic algorithm

Thomas Biekötter, María Olalla Olea-Romacho|arXiv (Cornell University)|Jan 1, 2021

Particle physics theoretical and experimental studiesPhysics and Astronomy171 references55 citations

TL;DR

This paper proposes a singlet-extended two-Higgs-doublet model (S2HDM) that realizes pseudo-Nambu-Goldstone (pNG) dark matter (DM) while satisfying Higgs sector constraints. Using a genetic algorithm, it demonstrates that the model can simultaneously account for the measured DM relic abundance, evade direct-detection limits via momentum-suppressed scattering, and accommodate the 96 GeV LEP and CMS excesses, all within perturbative and vacuum-stability bounds.

ABSTRACT

We investigate a possible realization ofpseudo-Nambu-Goldstone (pNG) dark matterin the framework of a singlet-extended 2 Higgsdoublet model (S2HDM). pNG dark matter gainedattraction due to the fact that direct-detectionconstraints can be avoided naturally because of themomentum-suppressed scattering cross sections,whereas the relic abundance of dark matter cannevertheless be accounted for via the usual thermalfreeze-out mechanism. We confront the S2HDM witha multitude of theoretical and experimentalconstraints, paying special attention to thetheoretical limitations on the scalar potential,such as vacuum stability and perturbativity.In addition, we discussthe complementarity between constraintsrelated to the dark matter sector, on theone hand, and to the Higgs sector, on the other hand.In our numerical discussion we explore theHiggs funnel region with dark mattermasses around 60GeV using a genetic algorithm.We demonstrate that the S2HDM can easilyaccount for the measured relic abundance whilebeing in agreement with all relevant constraints.We also discuss whether the so-calledcenter-of-galaxy excesses can beaccommodated,possibly incombination with a Higgsboson at about 96GeV that can be the originof the LEP- and the CMS-excess observed at this massin the $b \bar b$-quark andthe diphoton final state, respectively.

Motivation & Objective

• To explore a viable realization of pseudo-Nambu-Goldstone (pNG) dark matter in the S2HDM framework.
• To reconcile the observed dark matter relic abundance with stringent experimental and theoretical constraints.
• To investigate whether the S2HDM can explain the 96 GeV excesses observed in LEP and CMS data in the b¯b and diphoton final states.
• To assess the complementarity between constraints from the Higgs sector and the dark matter sector.
• To develop and publicly release a Python package, s2hdmTools, for model analysis and constraint application.

Proposed method

• Employing a genetic algorithm to scan the S2HDM parameter space, focusing on the Higgs funnel region with DM masses near 60 GeV.
• Applying theoretical constraints including vacuum stability, perturbativity up to 1 TeV, and tree-level unitarity bounds on quartic couplings.
• Using the HiggsBounds and HiggsSignals packages to test compatibility with LHC Higgs signal strength measurements.
• Implementing MicrOmegas and MadDM to compute the DM relic abundance and test indirect detection constraints from dwarf spheroidal galaxies.
• Utilizing the s2hdmTools Python package to automate the application of theoretical and experimental constraints across the parameter space.
• Transforming Lagrangian parameters into physical masses and mixing angles via rotation matrices derived from scalar mixing angles.

Experimental results

Research questions

• RQ1 Can the S2HDM with pNG dark matter simultaneously satisfy the measured dark matter relic abundance and avoid direct-detection constraints?
• RQ2 Is it possible to explain the 96 GeV excesses in the b¯b final state (LEP) and diphoton final state (CMS) within the S2HDM while maintaining perturbative unitarity and vacuum stability?
• RQ3 How do theoretical constraints—such as perturbativity up to 1 TeV and vacuum stability—affect the viable parameter space for the S2HDM with pNG DM?
• RQ4 Can the model simultaneously account for the galactic center excess and the antiproton excess without violating existing astrophysical limits?
• RQ5 What is the impact of the second Higgs doublet on the DM annihilation cross section and relic abundance compared to a single-doublet model?

Key findings

• The S2HDM can successfully reproduce the measured dark matter relic abundance (Ωh² = 0.119 ± 0.003) while satisfying all theoretical and experimental constraints.
• The model naturally evades direct-detection limits due to momentum-suppressed DM-nucleon scattering, a key feature of pNG dark matter.
• A singlet-like CP-even Higgs boson at 96 GeV can simultaneously explain the LEP b¯b excess and the CMS diphoton excess, provided mχ > m_h125/2 to allow for sufficient mixing with the 125 GeV Higgs.
• The model remains perturbative up to 1 TeV, with heavy scalar mass splittings (H±, A, h2,3) constrained to less than ~100 GeV, pushing the spectrum toward the decoupling limit.
• Simultaneous explanation of the 96 GeV collider excesses and cosmic-ray anomalies (galactic center and antiproton excesses) is possible in principle, but such points are disfavored by observations of dwarf spheroidal galaxies.
• The study provides a public Python package, s2hdmTools, which integrates HiggsBounds, HiggsSignals, MicrOmegas, and MadDM for automated model validation and constraint testing.