Fermionic Dark Matter Model Research Articles

High-energy neutrinos from multibody decaying dark matter

Since the report of the PeV-TeV neutrinos by the IceCube Collaboration, various particle physics models have been proposed to explain the neutrino spectrum by dark matter particles decaying into neutrinos and other Standard Model particles.In such scenarios, simultaneous $\gamma$-ray emission is commonly expected. Therefore, multi-messenger connections are generally important for the indirect searches of dark matters. The recent development of $\gamma$-ray astronomy puts stringent constraints on the properties of dark matter, especially by observations with the Fermi $\gamma$-ray satellite in the last several years. Motivated by the lack of $\gamma$-ray as well as the shape of the neutrino spectrum observed by IceCube, we discuss a scenario in which the DM is a PeV scale particle which couples strongly to other invisible particles and its decay products do not contain a charged particle. As an example to realize such possibilities, we consider a model of fermionic dark matter that decays into a neutrino and many invisible fermions. The dark matter decay is secluded in the sense that the emitted products are mostly neutrinos and dark fermions. One remarkable feature of this model is the resulting broadband neutrino spectra around the energy scale of the dark matter. We apply this model to multi-PeV dark matter, and discuss possible observable consequences in light of the IceCube data. In particular, this model could account for the large flux at medium energies of $\sim10-100$ TeV, possibly as well as the second peak at PeV, without violating the stringent $\gamma$-ray constraints from Fermi and air-shower experiments such as CASA-MIA.

Revisiting simplified dark matter models in terms of AMS-02 and Fermi-LAT

We perform an analysis of the simplified dark matter models in the light of cosmic ray observables by AMS-02 and Fermi-LAT. We assume fermion, scalar or vector dark matter particle with a leptophobic spin-0 mediator that couples only to Standard Model quarks and dark matter via scalar and/or pseudo-scalar bilinear. The propagation and injection parameters of cosmic rays are determined by the observed fluxes of nuclei from AMS-02. We find that the AMS-02 observations are consistent with the dark matter framework within the uncertainties. The AMS-02 antiproton data prefer 30 (50) GeV - 5 TeV dark matter mass and require an effective annihilation cross section in the region of 4 × 10−27 (7 × 10−27) - 4 × 10−24 cm3/s for the simplified fermion (scalar and vector) dark matter models. The cross sections below 2 × 10−26 cm3/s can evade the constraint from Fermi-LAT dwarf galaxies for about 100 GeV dark matter mass.

Two Higgs doublet dark matter portal

We study a fermionic dark matter model in which the interaction of the dark and visible sectors is mediated by Higgs portal type couplings. Specifically, we consider the mixing of a dark sector scalar with the scalars of a Two Higgs Doublet Model extension of the Standard Model. Given that scalar exchange will result in a spin-independent dark matter-nucleon scattering cross section, such a model is potentially subject to stringent direct detection constraints. Moreover, the addition of new charged scalars introduce non-trivial flavour constraints. Nonetheless, this model allows more freedom than a standard Higgs portal scenario involving a single Higgs doublet, and much of the interesting parameter space is not well approximated by a Simplified Model with a single scalar mediator. We perform a detailed parameter scan to determine the mass and coupling parameters which satisfy direct detection, flavour, precision electroweak, stability, and perturbativity constraints, while still producing the correct relic density through thermal freezeout.

Exploring a hidden fermionic dark sector

We propose a hidden sector fermion dark matter model which follows a dark SU(2) $$_\mathrm {H}$$ symmetry. Fermions in the dark sector also carry a global U(1) $$_\mathrm {H}$$ charge while the gauge bosons and dark scalar do not have any global U(1) $$_\mathrm {H}$$ charge. The lightest fermion in dark sector can serve as a potential dark matter candidate. We investigate whether the proposed dark matter candidate can explain indirect detection results from galactic centre.

Characterizing Higgs portal dark matter models at the ILC

We study the dark matter (DM) discovery prospect and its spin discrimination in the theoretical framework of gauge invariant and renormalizable Higgs portal DM models at the ILC with sqrt{s} = 500 GeV. In such models, the DM pair is produced in association with a Z boson. In the case of the singlet scalar DM, the mediator is just the SM Higgs boson, whereas for the fermion or vector DM there is an additional singlet scalar mediator that mixes with the SM Higgs boson, which produces significant observable differences. After careful investigation of the signal and backgrounds both at parton level and at detector level, we find the signal with hadronically decaying Z boson provides a better search sensitivity than the signal with leptonically decaying Z boson. Taking the fermion DM model as a benchmark scenario, when the DM-mediator coupling g_chi is relatively small, the DM signals are discoverable only for benchmark points with relatively light scalar mediator H_2. The spin discriminating from scalar DM is always promising, while it is difficult to discriminate from vector DM. As for g_chi approaching the perturbative limit, benchmark points with the mediator H_2 in the full mass region of interest are discoverable. The spin discriminating aspects from both the scalar and the fermion DM are quite promising.

Well-tempered n-plet dark matter

We study simple effective models of fermionic WIMP dark matter, where the dark matter candidate is a mixture of a Standard Model singlet and an n-plet of SU2L with n ≥ 3, stabilized by a discrete symmetry. The dark matter mass is assumed to be around the electroweak scale, and the mixing is generated by higher-dimensional operators, with a cutoff scale ≳TeV. For appropriate values of the mass parameters and the mixing we find that the observed dark matter relic density can be generated by coannihilation. Direct detection experiments have already excluded large parts of the parameter space, and the next-generation experiments will further constrain these models.

Mono-Higgs signature in a fermionic dark matter model

In light of the discovery of the Higgs boson we explore a mono-Higgs signature in association with dark matter pair production at the Large Hadron Collider (LHC) in a renormalizable model with a fermionic dark matter candidate. For two channels with γγ+MET and +MET in the final state we simulate the standard model (SM) backgrounds and signal events at TeV. We then estimate the LHC sensitivities for various benchmark points for two integrated luminosities and . We constrain the Yukawa coupling of the dark matter–SM interaction, taking into account bounds from mono-Higgs signature, observed dark matter relic density, Higgs physics, perturbativity requirement and electroweak measurements. Concerning the mono-Higgs search, it turns out that the channel with the largest branching ratio, the channel, provides better sensitivity. There are found regions in the parameter space of the model compatible with all the bounds mentioned above which can be reached in future LHC studies.

Analyzing of singlet fermionic dark matter via the updated direct detection data

We revisit the parameter space of singlet fermionic cold dark matter model in order to determine the role of the mixing angle between the standard model Higgs and a new singlet one. Furthermore, we restudy the direct detection constraints with the updated and new experimental data. As an important conclusion, this model is completely excluded by recent XENON100, PandaX II and LUX data.

Augury of darkness: the low-mass dark Z\u2032 portal

Dirac fermion dark matter models with heavy Z′ mediators are subject to stringent constraints from spin-independent direct searches and from LHC bounds, cornering them to live near the Z′ resonance. Such constraints can be relaxed, however, by turning off the vector coupling to Standard Model fermions, thus weakening direct detection bounds, or by resorting to light Z′ masses, below the Z pole, to escape heavy resonance searches at the LHC. In this work we investigate both cases, as well as the applicability of our findings to Majorana dark matter. We derive collider bounds for light Z′ gauge bosons using the CLS method, spin-dependent scattering limits, as well as the spin-independent scattering rate arising from the evolution of couplings between the energy scale of the mediator mass and the nuclear energy scale, and indirect detection limits. We show that such scenarios are still rather constrained by data, and that near resonance they could accommodate the gamma-ray GeV excess in the Galactic center.

Dark matter physics, flavor physics and LHC constraints in the dark matter model with a bottom partner

In the scenario that dark matter (DM) is a weakly interacting massive particle, there are many possibilities of the interactions with the Standard Model (SM) particles to achieve the relic density of DM. In this paper, we consider a simple DM model where the DM candidate is a complex scalar boson. The model contains a new complex gauge singlet scalar boson and a new fermion whose gauge charge is the same as the right-handed down-type quark. We dub the new fermion the bottom partner. These new particles have Yukawa interactions with the SM down-type quarks. The DM candidate interacts with the SM particles through the Yukawa interactions. The Yukawa interactions are not only relevant to the annihilation process of the DM but also contribute to the flavor physics, such as the ΔF = 2 processes. In addition, the flavor alignment of the Yukawa couplings is related to the decay modes of the bottom partner, and thus we can find the explicit correlations among the physical observables in DM physics, flavor physics, and the signals at the LHC. We survey the ΔF = 2 processes based on the numerical analyses of the thermal relic density, the direct detection of the DM, and the current LHC bounds. We investigate the perturbative bound on the Yukawa coupling as well. A Study of a fermionic DM model with extra scalar quarks is also given for comparison.

Simplified dark matter models with charged mediators: prospects for direct detection

We consider direct detection prospects for a class of simplified models of fermionic dark matter (DM) coupled to left and right-handed Standard Model fermions via two charged scalar mediators with arbitrary mixing angle $\alpha$. DM interactions with the nucleus are mediated by higher electromagnetic moments, which, for Majorana DM, is the anapole moment. After giving a full analytic calculation of the anapole moment, including its $\alpha$ dependence, and matching with limits in the literature, we compute the DM-nucleon scattering cross-section and show the LUX and future LZ constraints on the parameter space of these models. We then compare these results with constraints coming from $Fermi$-LAT continuum and line searches. Results in the supersymmetric limit of these simplified models are provided in all cases. We find that future direct detection experiments will be able to probe most of the parameter space of these models for $\mathcal{O}(100-200)$ GeV DM and lightest mediator mass $\lesssim \mathcal{O}(5\%)$ larger than the DM mass. The direct detection prospects dwindle for larger DM mass and larger mass gap between the DM and the lightest mediator mass, although appreciable regions are still probed for $\mathcal{O}(200)$ GeV DM and lightest mediator mass $\lesssim \mathcal{O}(20\%)$ larger than the DM mass. The direct detection bounds are also attenuated near certain "blind spots" in the parameter space, where the anapole moment is severely suppressed due to cancellation of different terms. We carefully study these blind spots and the associated $Fermi$-LAT signals in these regions.

Connecting the LHC diphoton excess to the Galatic Center gamma-ray excess

The recent LHC Run-2 data have shown a possible excess in diphoton events, suggesting the existence of a new resonance $\phi$ with mass $M\sim 750$~GeV. If $\phi$ plays the role of a portal particle connecting the Standard Model and the invisible dark sector, the diphoton excess should be correlated with another photon excess, namely, the excess in the diffuse gamma rays towards the Galactic center, which can be interpreted by the annihilation of dark matter(DM). We investigate the necessary conditions for a consistent explanation for the two photon excesses, especially the requirement on the width-to-mass ratio $\Gamma/M$ and $\phi$ decay channels, in a collection of DM models where the DM particle can be scalar, fermionionic and vector, and $\phi$ can be generated through $s$-channel $gg$ fusion or $q\bar q$ annihilation. We show that the minimally required $\Gamma/M$ is determined by a single parameter proportional to $(m_{\chi}/M)^{n}$, where the integer $n$ depends on the nature of the DM particle. We find that for the scalar DM model with $\phi$ generated from $q\bar q$ annihilation, the minimally required $\Gamma/M$ can be as low as $\mathcal{O}(10^{-3})$. For the scalar DM model with $\phi$ generated from $gg$ fusion and fermionic DM model with $\phi$ from $q\bar q$ annihilation, the required $\Gamma/M$ are typically of $\mathcal{O}(10^{-2})$. The vector DM models, however, require very large $\Gamma/M$ of order one. For the DM models which can consistently explain both the excesses,the predicted cross sections for gamma-ray line are typically of $\mathcal{O}(10^{-31}-10^{-29})~\text{cm}^{3}\text{s}^{-1}$, which are close to the current limits from the Fermi-LAT experiment.

Secluded singlet fermionic dark matter driven by the Fermi gamma-ray excess

We examine the possibility that the dark matter (DM) interpretation of the GeV scale Fermi gamma-ray excess at the Galactic Center can be realized in a specific framework - secluded singlet fermionic dark matter model with small mixing between the dark and Standard Model sector. Within this framework it is shown that the DM annihilation into bottom-quark pair, Higgs pair, and new scalar pair can give good fits to the Fermi gamma-ray data. Moreover unavoidable constraints from the antiproton ratio by the PAMELA and AMS-02, the gamma-ray emission from the dwarf spheroidal galaxies by the Fermi-LAT, and the Higgs measurements by the LHC are also considered. Then we found our best-fit parameters for the Fermi gamma-ray excess without conflicting other experimental and cosmological constraints if uncertainties on the DM density profile of the Milky Way Galaxy are taken into account. Successfully surviving parameters are benchmark points for future study on the collider signals.

GeV dark matter searches with the NEWS detector

The proposed NEWS apparatus, a spherical detector with a small central electrode sensor operating as a proportional counter, promises to explore new swaths of the direct detection parameter space in the GeV and sub-GeV dark matter particle mass range by employing very light nuclear targets, such as H and He, and by taking advantage of a very low (sub-keV) energy threshold. Here we discuss and study two example classes of dark matter models that will be tested with NEWS: GeV-scale millicharged dark matter, and a GeV-Dirac Fermion dark matter model with a light (MeV-GeV) scalar or vector mediator, and indicate the physical regions of parameter space the experiment can probe.

Beyond the dark matter effective field theory and a simplified model approach at colliders

Direct detection of and LHC search for the singlet fermion dark matter (SFDM) model with Higgs portal interaction are considered in a renormalizable model where the full Standard Model (SM) gauge symmetry is imposed by introducing a singlet scalar messenger. In this model, direct detection is described by an effective operator m_q \bar{q} q \bar{\chi} \chi as usual, but the full amplitude for monojet + \not E_T involves two intermediate scalar propagators, which cannot be seen within the effective field theory (EFT) or in the simplified model without the full SM gauge symmetry. We derive the collider bounds from the ATLAS monojet + \not E_T as well as the CMS t\bar{t} + \not E_T data, finding out that the bounds and the interpretation of the results are completely different from those obtained within the EFT or simplified models. It is pointed out that it is important to respect unitarity, renormalizability and local gauge invariance of the SM.

The Fermi-LAT gamma-ray excess at the Galactic Center in the singlet-doublet fermion dark matter model

The singlet-doublet fermion dark matter model (SDFDM) provides a good DM candidate as well as the possibility of generating neutrino masses radiatively. The search and identification of DM requires the combined effort of both indirect and direct DM detection experiments in addition to the LHC. Remarkably, an excess of GeV gamma rays from the Galactic Center (GCE) has been measured with the Fermi Large Area Telescope (LAT) which appears to be robust with respect to changes in the diffuse galactic background modeling. Although several astrophysical explanations have been proposed, DM remains a simple and well motivated alternative. In this work, we examine the sensitivities of dark matter searches in the SDFDM scenario using Fermi-LAT, CTA, IceCube/DeepCore, LUX, PICO and LHC with an emphasis on exploring the regions of the parameter space that can account for the GCE. We find that DM particles present in this model with masses close to ∼ 99 GeV and ∼ (173–190) GeV annihilating predominantly into the W+W− channel and tt̄ channel respectively, provide an acceptable fit to the GCE while being consistent with different current experimental bounds. We also find that much of the obtained parameter space can be ruled out by future direct search experiments like LZ and XENON-1T, in case of null results by these detectors. Interestingly, we show that the most recent data by LUX is starting to probe the best fit region in the SDFDM model.

Majorana dark matter through a narrow Higgs portal

We consider the Singlet Majorana fermion dark matter model, in which the standard model particles interact with the dark sector through the mixing of a singlet scalar and the Higgs boson. In this model both the dark matter and the singlet scalar carry lepton number, the latter being a bilepton. We suppose the existence of a $Z_2$ symmetry, remnant of some high energy local symmetry breaking, that stabilizes the Majorana fermion. We analyzed the parameter space of this model and found that the lepton number symmetry breaking scale, drove by the singlet scalar, is constrained to be within hundreds to thousands of GeV, so as to conform with the observed dark matter relic density. Finally, we address the direct detection and invisible Higgs decay complementarity, confronting our model with recent LUX and LHC constraints, as well as XENON1T prospects.

Extension of minimal fermionic dark matter model: a study with two Higgs doublet model

We explore a fermionic dark matter model with a possible extension of Standard Model (SM) of particle physics into two Higgs doublet model. Higgs doublets couple to the singlet fermionic dark matter (FDM) through a non renormalisable coupling providing a new physics scale. We explore the viability of such dark matter candidate and constrain the model parameter space by collider serach, relic density of DM, direct detection measurements of DM-nucleon scattreing cross-section and with the experimentally obtained results from indirect search of dark matter.

Radiative neutrino masses in the singlet-doublet fermion dark matter model with scalar singlets

When the singlet-doublet fermion dark matter model is extended with additional ${Z}_{2}$-odd real singlet scalars, neutrino masses and mixings can be generated at the one-loop level. In this work, we discuss the salient features arising from the combination of the two resulting simplified dark matter models. When the lightest ${Z}_{2}$-odd particle is a scalar singlet, $\mathrm{Br}(\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma})$ could be measurable provided that the singlet-doublet fermion mixing is small enough. In this scenario, the new decay channels of vector-like fermions into scalars can also generate interesting leptonic plus missing transverse energy signals at the LHC. On the other hand, in the case of doublet-like fermion dark matter, scalar coannihilations lead to an increase in the relic density which allows one to lower the bound of doublet-like fermion dark matter.

Dark matter massive fermions and Einasto profiles in galactic haloes

On the basis of a fermionic dark matter model we fit rotation curves of The HI Nearby Galaxy Survey THINGS sample and compare our 3-parametric model to other models widely used in the literature: 2-parametric Navarro--Frenk--White, pseudoisothermal sphere, Burkhert models, and 3-parametric Einasto model, suggested as the new "standard dark matter profile" model in the paper by Chemin et. al., AJ 142 (2011) 109. The results from the fitting procedure provides evidence for an underlying fermionic nature of the dark matter candidate, with rest mass above the keV regime.