Dark Higgs Boson Research Articles

Muon (g − 2) and thermal WIMP DM in U1Lμ−Lτ models

The U1Lμ−Lτ model is anomaly-free with the Standard Model (SM) fermion content, and can make substantial contributions to the muon (g − 2) at the level of ∆aμ ∼ O(10) × 10−10 for MZ′ ∼ O(10 − 100) MeV and gX ∼ (4 − 8) × 10−4. In this light Z′ region, it was claimed that the model can also incorporate thermal WIMP dark matter (DM) if MDM ∼ MZ′/2. This setup relies on DM particles annihilating into SM particles through a Z′-mediated s-channel. In this work, we show that this tight relationship between MZ′ and MDM can be evaded or nullified both for scalar and spin-1/2 DM by considering the contributions from the dark Higgs boson (H1). The dark Higgs boson plays an important role, not only because it gives mass to the dark photon but also because it introduces additional DM annihilation channels, including new final states such as H1H1, Z′Z′, and Z′H1. As a result, the model does not require a close mass correlation between the Z′ boson and dark matter MDM ~ MZ′/2 any longer, allowing for a broader range of mass possibilities for both scalar and fermionic dark matter types. We explore in great details various scenarios where the U(1) symmetry is either fully broken or partially remains as discrete symmetries, Z2 or Z3. This approach broadens the model’s capacity to accommodate various WIMP dark matter phenomena in the light Z′ region where the muon (g − 2)μ makes a sensitive probe of the model.

Hadronic mono-W′ probes of dark matter at colliders

Particle collisions at the energy frontier can probe the nature of invisible dark matter via production in association with recoiling visible objects. We propose a new potential production mode, in which dark matter is produced by the decay of a heavy dark Higgs boson radiated from a heavy W′ boson. In such a model, motivated by left-right symmetric theories, dark matter would not be pair produced in association with other recoiling objects due to its lack of direct coupling to quarks or gluons. We study the hadronic decay mode via W′ → tb and estimate the LHC exclusion sensitivity at 95% confidence level to be 102 − 105 fb for W′ boson masses between 250 and 1750 GeV.

Search for dark matter particles in W+W− events with transverse momentum imbalance in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV

A search for dark matter particles is performed using events with a pair of W bosons and large missing transverse momentum. Candidate events are selected by requiring one or two leptons (ℓ = electrons or muons). The analysis is based on proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC and corresponding to an integrated luminosity of 138 fb−1. No significant excess over the expected standard model background is observed in the ℓνqq and 2ℓ2ν final states of the W+W− boson pair. Limits are set on dark matter production in the context of a simplified dark Higgs model, with a dark Higgs boson mass above the W+W− mass threshold. The dark matter phase space is probed in the mass range 100–300 GeV, extending the scope of previous searches. Current exclusion limits are improved in the range of dark Higgs masses from 160 to 250 GeV, for a dark matter mass of 200 GeV.

Search for Dark Photons in Rare Z Boson Decays with the ATLAS Detector.

A search for events with a dark photon produced in association with a dark Higgs boson via rare decays of the standard model Z boson is presented, using 139 fb^{-1} of sqrt[s]=13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. The dark boson decays into a pair of dark photons, and at least two of the three dark photons must each decay into a pair of electrons or muons, resulting in at least two same-flavor opposite-charge lepton pairs in the final state. The data are found to be consistent with the background prediction, and upper limits are set on the dark photon's coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, α_{D}ϵ^{2}, in the dark photon mass range of [5, 40]GeV except for the ϒ mass window [8.8, 11.1]GeV. This search explores new parameter space not previously excluded by other experiments.

Search for dark matter produced in association with a dark Higgs boson decaying into W+W− in the one-lepton final state at sqrt{s} = 13 TeV using 139 fb−1 of pp collisions recorded with the ATLAS detector

Several extensions of the Standard Model predict the production of dark matter particles at the LHC. A search for dark matter particles produced in association with a dark Higgs boson decaying into W+W− in the {ell}^{pm}nu q{overline{q}}^{prime }, final states with ℓ = e, μ is presented. This analysis uses 139 fb−1 of pp collisions recorded by the ATLAS detector at a centre-of-mass energy of 13 TeV. The W± → qoverline{q^{prime }} decays are reconstructed from pairs of calorimeter-measured jets or from track-assisted reclustered jets, a technique aimed at resolving the dense topology from a pair of boosted quarks using jets in the calorimeter and tracking information. The observed data are found to agree with Standard Model predictions. Scenarios with dark Higgs boson masses ranging between 140 and 390 GeV are excluded.

Probing a light dark sector at future lepton colliders via invisible decays of the SM-like and dark Higgs bosons

A renormalizable UV model for axionlike particles or hidden photons, which may explain the dark matter, usually involves a dark Higgs field, which is a singlet under the standard model (SM) gauge group. The dark sector can couple to the SM particles via the portal coupling between the SM-like Higgs and dark Higgs fields. Through this coupling, the dark sector particles can be produced in either the early Universe or the collider experiments. Interestingly, not only the SM-like Higgs boson can decay into the light dark bosons, but also a light dark Higgs boson may be produced and decay into the dark bosons in a collider. In this paper, we perform the first collider search for invisible decays by taking both the Higgs bosons into account. We use a multivariate technique to best discriminate the signal from the background. We find that a large parameter region can be probed at the International Linear Collider operating at the center-of-mass energy of 250 GeV. In particular, even when the SM-like Higgs invisible decay is a few orders of magnitude below the planned sensitivity reaches of the International Linear Collider and the high luminosity LHC, the scenario can be probed by the invisible decay of the dark Higgs boson produced via a similar diagram. Measuring the dark Higgs boson decay into the dark sector will be a smoking gun signal of the light dark sector. A similar search of the dark sector would be expected in, e.g., the Cool Copper Collider, the Circular Electron Positron Collider, the Compact Linear Collider, and the Future Circular electron-positron Collider.

Search for a Dark Photon and an Invisible Dark Higgs Boson in μ^{+}μ^{-} and Missing Energy Final States with the Belle II Experiment.

The dark photon A^{'} and the dark Higgs boson h^{'} are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of A^{'} and h^{'} in the dark Higgsstrahlung process e^{+}e^{-}→A^{'}h^{'} with A^{'}→μ^{+}μ^{-} and h^{'} invisible in electron-positron collisions at a center-of-mass energy of 10.58GeV in data collected by the Belle II experiment in 2019. With an integrated luminosity of 8.34 fb^{-1}, we observe no evidence for signal. We obtain exclusion limits at 90% Bayesian credibility in the range of 1.7-5.0fb on the cross section and in the range of 1.7×10^{-8}-200×10^{-8} on the effective coupling ϵ^{2}×α_{D} for the A^{'} mass in the range of 4.0 GeV/c^{2}<M_{A^{'}}<9.7 GeV/c^{2} and for the h^{'} mass M_{h^{'}}<M_{A^{'}}, where ϵ is the mixing strength between the standard model and the dark photon and α_{D} is the coupling of the dark photon to the dark Higgs boson. Our limits are the first in this mass range.

Inelastic dark matter from dark Higgs boson decays at FASER

We consider inelastic dark matter scenarios with dark photon mediator and a dark Higgs boson. The dark Higgs boson spontaneously breaks the gauge symmetry associated with the dark photon, and gives the mass to the dark photon and the mass difference to dark particles. Such a dark Higgs boson can decay into the dark particles and hence can be another source of the dark particles at collider experiments. We analyze the sensitivity to decays of the excited state into the dark matter and charged particles at the FASER 2 experiment in fermion and scalar inelastic dark matter scenarios. We consider two mass spectra as illustrating examples in which the excited state can be produced only through the decay of dark Higgs boson. We show that unprobed parameter region can be explored in fermion dark matter scenario for the illustrating mass spectra.

Effective field theory of Stückelberg vector bosons

We explore the effective field theory of a vector field ${X}^{\ensuremath{\mu}}$ that has a St\"uckelberg mass. The absence of a gauge symmetry for ${X}^{\ensuremath{\mu}}$ implies Lorentz-invariant operators are constructed directly from ${X}^{\ensuremath{\mu}}$. Beyond the kinetic and mass terms, allowed interactions at the renormalizable level include ${X}_{\ensuremath{\mu}}{X}^{\ensuremath{\mu}}{H}^{\ifmmode\dagger\else\textdagger\fi{}}H$, $({X}_{\ensuremath{\mu}}{X}^{\ensuremath{\mu}}{)}^{2}$, and ${X}_{\ensuremath{\mu}}{j}^{\ensuremath{\mu}}$, where ${j}^{\ensuremath{\mu}}$ is a global current of the SM or of a hidden sector. We show that all of these interactions lead to scattering amplitudes that grow with powers of $\sqrt{s}/{m}_{X}$, except for the case of ${X}_{\ensuremath{\mu}}{j}^{\ensuremath{\mu}}$ where ${j}^{\ensuremath{\mu}}$ is a nonanomalous global current. The latter is well known when $X$ is identified as a dark photon coupled to the electromagnetic current, often written equivalently as kinetic mixing between $X$ and the photon. The power counting for the energy growth of the scattering amplitudes is facilitated by isolating the longitudinal enhancement. We examine in detail the interaction with an anomalous global vector current ${X}_{\ensuremath{\mu}}{j}_{\mathrm{anom}}^{\ensuremath{\mu}}$, carefully isolating the finite contribution to the fermion triangle diagram. We calculate the longitudinally-enhanced observables $Z\ensuremath{\rightarrow}X\ensuremath{\gamma}$ (when ${m}_{X}&lt;{m}_{Z}$), $f\overline{f}\ensuremath{\rightarrow}X\ensuremath{\gamma}$, and $Z\ensuremath{\gamma}\ensuremath{\rightarrow}Z\ensuremath{\gamma}$ when $X$ couples to the baryon number current. Introducing a ``fake'' gauge-invariance by writing ${X}^{\ensuremath{\mu}}={A}^{\ensuremath{\mu}}\ensuremath{-}{\ensuremath{\partial}}^{\ensuremath{\mu}}\ensuremath{\pi}/{m}_{X}$, the would-be gauge anomaly associated with ${A}_{\ensuremath{\mu}}{j}_{\mathrm{anom}}^{\ensuremath{\mu}}$ is canceled by ${j}_{\mathrm{anom}}^{\ensuremath{\mu}}{\ensuremath{\partial}}_{\ensuremath{\mu}}\ensuremath{\pi}/{m}_{X}$; this is the four-dimensional Green-Schwarz anomaly-cancellation mechanism at work. Our analysis demonstrates there is a much larger set of possible interactions that an EFT with a St\"uckelberg vector field can have, revealing scattering amplitudes that grow with energy. The growth of these amplitudes can be tamed by a dark Higgs sector, but this requires dark Higgs boson interactions (and reintroduces fine-tuning in the dark Higgs sector) that can be separated from $X$ interactions only in the limit $g\ensuremath{\ll}1$.

Connecting dark gauge symmetry to the standard model

Dark matter is postulated to be a neutral Dirac fermion, charged under a dark U(1)D gauge symmetry. Scalar partners of the quarks and leptons are also charged under U(1)D. The dark gauge boson ZD and the dark Higgs boson hD enable either freeze-out or freeze-in mechanisms to account for the correct dark matter relic abundance. Dark number D is connected to baryon number B and lepton number L through D=3B+L−(2j)[mod2] where j is the intrinsic spin of the particle.

FACET: a new long-lived particle detector in the very forward region of the CMS experiment

We describe a proposal to add a set of very forward detectors to the CMS experiment for the high-luminosity era of the Large Hadron Collider to search for beyond the standard model long-lived particles, such as dark photons, heavy neutral leptons, axion-like particles, and dark Higgs bosons. The proposed subsystem is called FACET for Forward-Aperture CMS ExTension, and will be sensitive to any particles that can penetrate at least 50 m of magnetized iron and decay in an 18 m long, 1 m diameter vacuum pipe. The decay products will be measured in detectors using identical technology to the planned CMS Phase-2 upgrade.

Search for Dark Higgs Inflation with Curvature Corrections at LHC Experiments

We analyse the dark Higgs inflation model with curvature corrections and explore the possibility to test its predictions by the particle physics experiments at LHC. We show that the dark Higgs inflation model with curvature corrections is strongly favoured by the present cosmological observation. The cosmological predictions of this model, including the quantum corrections of dark Higgs coupling constants and the uncertainty in estimation of the reheating temperature, lead to the dark Higgs mass mφ=0.919± 0.211 GeV and the mixing angle (at 68% CL). We evaluate the FASER and MAPP-1 experiments reach for dark Higgs inflation mass and mixing angle in the 95% CL cosmological confidence region for an integrated luminosity of 3ab−1 at 13 TeV LHC, assuming 100% detection efficiency. We conclude that the dark Higgs inflation model with curvature corrections is a compelling inflation scenario based on particle physics theory favoured by the present cosmological measurements that can leave imprints in the dark Higgs boson searchers at LHC.

Muon g-2, dark matter and the Higgs mass in no-scale supergravity

We discuss the phenomenology of no-scale supergravity (SUGRA), in which the universal scalar mass is zero at the high scale, focussing on the recently updated muon g-2 measurement, and including dark matter and the correct Higgs boson mass. Such no-scale supergravity scenarios arise naturally from string theory and are also inspired by the successful Starobinsky inflation, with a class of minimal models leading to a strict upper bound on the gravitino mass m3/2<103 TeV. We perform a Monte Carlo scan over the allowed parameter space, assuming a mixture of pure gravity mediated and universal gaugino masses, using the SPheno package linked to FeynHiggs, MicrOmegas and CheckMate, displaying the results in terms of a Likelihood function. We present results for zero and non-zero trilinear soft parameters, and for different signs of gaugino masses, giving a representative set of benchmark points for each viable region of parameter space. We find that, while no-scale SUGRA can readily satisfy the dark matter and Higgs boson mass requirements, consistent with all other phenomenological constraints, the muon g-2 measurement may be accommodated only in certain regions of parameter space, close to the LHC excluded regions for light sleptons and charginos.

Turn up the volume: listening to phase transitions in hot dark sectors

Stochastic gravitational wave (GW) backgrounds from first-order phase transitions are an exciting target for future GW observatories and may enable us to study dark sectors with very weak couplings to the Standard Model. In this work we show that such signals may be significantly enhanced for hot dark sectors with a temperature larger than the one of the SM thermal bath. The need to transfer the entropy from the dark sector to the SM after the phase transition can however lead to a substantial dilution of the GW signal. We study this dilution in detail, including the effect of number-changing processes in the dark sector (so-called cannibalism), and show that in large regions of parameter space a net enhancement remains. We apply our findings to a specific example of a dark sector containing a dark Higgs boson and a dark photon and find excellent detection prospects for LISA and the Einstein telescope.

Seesaw lepton masses and muon $$g-2$$ from heavy vector-like leptons

We propose a model for the vector-like lepton to explain the small muon mass by a seesaw mechanism, based on lepton-specific two Higgs doublet models with a local $U(1)'$ symmetry. There is no bare muon mass for a nonzero $U(1)'$ charge of the leptophilic Higgs doublet, so the physical muon mass is generated due to the mixing between the vector-like lepton and the muon after the leptophilic Higgs doublet and the dark Higgs get VEVs. In this scenario, the non-decoupling effects of the vector-like lepton give rise to leading contributions to the muon $g-2$, thanks to the light $Z'$ and the light dark Higgs boson. We discuss various constraints on the model from lepton flavor violation, electroweak precision and Higgs data, as well as collider searches.

Multi-track displaced vertices at B-factories

We propose a program at B-factories of inclusive, multi-track displaced vertex searches, which are expected to be low background and give excellent sensitivity to non-minimal hidden sectors. Multi-particle hidden sectors often include long-lived particles (LLPs) which result from approximate symmetries, and we classify the possible decays of GeV-scale LLPs in an effective field theory framework. Considering several LLP production modes, including dark photons and dark Higgs bosons, we study the sensitivity of LLP searches with different number of displaced vertices per event and track requirements per displaced vertex, showing that inclusive searches can have sensitivity to a large range of hidden sector models that are otherwise unconstrained by current or planned searches.

Forward experiment sensitivity estimator for the LHC and future hadron colliders

We introduce a numerical package FORward Experiment SEnsitivity Estimator, or $\mathtt{FORESEE}$, that can be used to simulate the expected sensitivity reach of experiments placed in the far-forward direction from the proton-proton interaction point. The simulations can be performed for 14 TeV collision energy characteristic for the LHC, as well as for larger energies; 27 and 100 TeV. In the package, a comprehensive list of validated forward spectra of various SM species is also provided. The capabilities of $\mathtt{FORESEE}$ are illustrated for the popular dark photon and dark Higgs boson models, as well as for the search for light up-philic scalars. For the dark photon portal, we also comment on the complementarity between such searches and dark matter direct detection bounds. Additionally, for the first time, we discuss the prospects for the LLP searches in the proposed future hadron colliders: High-Energy LHC (HE-LHC), Super proton-proton Collider (SppC), and Future Circular Collider (FCC-hh).

Long-lived dark Higgs and inelastic dark matter at Belle II

Inelastic dark matter is an interesting scenario for light thermal dark matter which is fully consistent with all cosmological probes as well as direct and indirect dark matter detection. The required mass splitting between dark matter χ1 and its heavier twin χ2 is naturally induced by a dark Higgs field which also provides a simple mechanism to give mass to the dark photon A′ present in the setup. The corresponding dark Higgs boson h′ is naturally the lightest dark sector state and therefore decays into Standard Model particles via Higgs mixing. In this work we study signatures with displaced vertices and missing momentum at Belle II, arising from dark Higgs particles produced in association with dark matter. We find that Belle II can be very sensitive to this scenario, in particular if a displaced vertex trigger is available in the near future.

On the challenges of searching for GeV-scale long-lived particles at the LHC

Many models of dark matter predict long-lived particles (LLPs) that can give rise to striking signatures at the LHC. Existing searches for displaced vertices are however tailored towards heavy LLPs. In this work we show that this bias severely affects their sensitivity to LLPs with masses at the GeV scale. To illustrate this point we consider two dark sector models with light LLPs that decay hadronically: a strongly-interacting dark sector with long-lived exotic mesons, and a Higgsed dark sector with a long-lived dark Higgs boson. We study the sensitivity of an existing ATLAS search for displaced vertices and missing energy in these two models and find that current track and vertex cuts result in very low efficiency for light LLPs. To close this gap in the current search programme we suggest two possible modifications of the vertex reconstruction and the analysis cuts. We calculate projected exclusion limits for these modifications and show that they greatly enhance the sensitivity to LLPs with low mass or short decay lengths.

Search for Dark Matter Produced in Association with a Dark Higgs Boson Decaying into W^{±}W^{∓} or ZZ in Fully Hadronic Final States from sqrt[s]=13 TeV pp Collisions Recorded with the ATLAS Detector.

Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV=W^{±}W^{∓} or ZZ pairs from a decay of a dark Higgs boson s is searched for using 139 fb^{-1} of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13TeV. The s→V(qq[over ¯])V(qq[over ¯]) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with m_{s}>160 GeV are excluded.