Fermionic Dark Matter Research Articles

New wave function formed by fermionic dark matter

New wave function formed by fermionic dark matter

GeV-scale inelastic dark matter with dark photon mediator via direct detection and cosmological and laboratory constraints

We propose a new candidate of GeV scale inelastic dark matter (DM). Our construction has an anomaly-free $U(1)_X^{}$ gauge group with dark photon mediator, and can realize either scalar or fermionic inelastic DM. It is highly predictive and testable. We study the scattering rate of light inelastic DM with electrons in the XENON1T experiment and with nuclei in the XENON1T, CRESST-III, CDEX-1B and DarkSide-50 experiments. We resolve the recent XENON1T anomaly via electron recoil detection. Combining the XENON1T constraints from both electron recoils and nuclear recoils (including Migdal effect), we predict the inelastic DM mass $\lesssim 1.5$GeV. We further analyze the bounds by the DM relic abundance, the lifetime of the heavier DM component, and laboratory constraints, from which we identify the viable parameter space for the future probe. This provides an important benchmark for the theories and experimental tests of GeV scale inelastic DM.

Phenomenology of dark matter and mirror fermions from a left–right mirror model with singlet scalar

We investigate a left–right mirror model with SU(3) c × SU(2)L × SU(2)R × U(1) Y and a discrete symmetry, which introduces mirror fields that are copies of the standard model (SM) fields. The mirror fields have the opposite chirality to their SM counterpart fields. We also introduce singlet scalars as dark matter (DM). The new interaction between DM, SM fermions, and mirror fermions can account for DM abundance, charged lepton flavor violation, lepton anomalous magnetic moment, and flavor changing neutral current. We demonstrated that if we choose DM annihilation into muon as the dominant annihilation channel for leptophilic DM, both the observed DM abundance and the observed discrepancy between theory and experiment in the muon anomalous magnetic moment can be explained without contradicting the bound derived from charged lepton flavor violating processes. We briefly discuss how mirror fermions will be produced at the future linear collider, as mirror fermions can interact with neutral gauge bosons in this model. Finally, we discuss the lightest mirror neutrino decay mechanism, which will be highly abundant if stable.

What does lie at the Milky Way centre? Insights from the S2-star orbit precession

ABSTRACT It has been recently demonstrated that both, a classical Schwarzschild black hole (BH), and a dense concentration of self-gravitating fermionic dark matter (DM) placed at the Galaxy centre, can explain the precise astrometric data (positions and radial velocities) of the S-stars orbiting Sgr A*. This result encompasses the 17 best resolved S-stars, and includes the test of general relativistic effects such as the gravitational redshift in the S2-star. In addition, the DM model features another remarkable result: The dense core of fermions is the central region of a continuous density distribution of DM whose diluted halo explains the Galactic rotation curve. In this Letter, we complement the above findings by analysing in both models the relativistic periapsis precession of the S2-star orbit. While the Schwarzschild BH scenario predicts a unique prograde precession for S2, in the DM scenario, it can be either retrograde or prograde, depending on the amount of DM mass enclosed within the S2 orbit, which, in turn, is a function of the DM fermion mass. We show that all the current and publicly available data of S2 cannot discriminate between the two models, but upcoming S2 astrometry close to next apocentre passage could potentially establish if Sgr A* is governed by a classical BH or by a quantum DM system.

Fermionic singlet dark matter in one-loop solutions to the R_K anomaly: a systematic study

We study the dark matter phenomenology of Standard Model extensions addressing the reported anomaly in the R_K observable at one-loop. The article covers the case of fermionic singlet DM coupling leptophilically, quarkphilically or amphiphilically to the SM. The setup utilizes a large coupling of the new particle content to the second lepton generation to explain the R_K anomaly, which in return tends to diminish the dark matter relic density. Further, dark matter direct detection experiments provide stringent bounds even in cases where the dark matter candidate only contributes a small fraction of the observed dark matter energy density. In fact, direct detection rules out all considered models as an explanation for the R_K anomaly in the case of Dirac dark matter. Conversely, for Majorana dark matter, the R_K anomaly can be addressed in agreement with direct detection in coannihilation scenarios. For leptophilic dark matter this region only exists for M_text {DM} lesssim 1000 , mathrm {GeV} and dark matter is underabundant. Quarkphilic and amphiphilic scenarios even provide narrow regions of parameter space where the observed relic density can be reproduced while offering an explanation to R_K in agreement with direct detection experiments.

Probing dark matter-cosmic ray electron interactions with circular polarisation of photons

Conventional indirect dark matter (DM) searches look for an excess in the electromagnetic emission from the sky that cannot be attributed to known astrophysical sources, but its polarisation has not been explored to date. In this proceeding, I argue that photon polarisation is an important feature to understand new physics interactions. Circular polarisation can be generated from Beyond the Standard Model interactions if they violate parity and there is an asymmetry in the number density of the initial state particles which participate in the interaction. I consider a simplified model for fermionic (Majorana) DM and study the circularly polarised gamma rays from DM cosmic ray electron interactions. I study the differential flux of positive and negative polarised photons from the Galactic Centre and show that the degree of circular polarization can reach up to 90%. Finally, I discuss the detection prospects of this signal in future experiments.

Circular polarisation of gamma rays as a probe of dark matter interactions with cosmic ray electrons

Conventional indirect dark matter (DM) searches look for an excess in the electromagnetic emission from the sky that cannot be attributed to known astrophysical sources. Here, we argue that the photon polarisation is an important feature to understand new physics interactions and can be exploited to improve our sensitivity to DM. In particular, circular polarisation can be generated from Beyond the Standard Model interactions if they violate parity and there is an asymmetry in the number of particles which participate in the interaction. In this work, we consider a simplified model for fermionic (Majorana) DM and study the circularly polarised gamma rays below 10 GeV from the scattering of cosmic ray electrons on DM. We calculate the differential flux of positive and negative polarised photons from the Galactic Center and show that the degree of circular polarisation can reach up to 90%. Finally, once collider and DM constraints have been taken into account, we estimate the required sensitivity from future experiments to detect this signal finding that, although a distinctive peak will be present in the photon flux spectrum, a near future observation is unlikely. However, different sources or models not considered in this work could provide higher intensity fluxes, leading to a possible detection by e-ASTROGAM. In the event of a discovery, we argue that the polarisation fraction is a valuable characterisation feature of the new sector.

Dark matter and lepton flavour phenomenology in a singlet-doublet scotogenic model

We study the dark matter phenomenology of scotogenic frameworks through a rather illustrative model extending the Standard Model by scalar and fermionic singlets and doublets. Such a setup is phenomenologically attractive since it provides the radiative generation of neutrino masses, while also including viable candidates for cold dark matter. We employ a Markov Chain Monte Carlo algorithm to explore the associated parameter space in view of numerous constraints stemming from the Higgs mass, the neutrino sector, dark matter, and lepton-flavour violating processes. After a general discussion of the results, we focus on the case of fermionic dark matter, which remains rather uncovered in the literature so far. We discuss the associated phenomenology and show that in this particular case a rather specific mass spectrum is expected with fermion masses just above 1 TeV. Our study may serve as a guideline for future collider studies.

Warm Dark Matter from Higher-Dimensional Gauge Theories

Warm dark matter particles with masses in the keV range have been linked with the large group representations in gauge theories through a high number of species at decoupling. In this paper, we address WDM fermionic degrees of freedom from such representations. Bridging higher-dimensional particle physics theories with cosmology studies and astrophysical observations, our approach is two-folded, i.e., it includes realistic models from higher-dimensional representations and constraints from simulations tested against observations. Starting with superalgebras in exceptional periodicity theories, we discuss several symmetry reductions and we consider several representations that accommodate a high number of degrees of freedom. We isolate a model that naturally accommodates both the standard model representation and the fermionic dark matter in agreement with both large and small-scale constraints. This model considers an intersection of branes in D = 27 + 3 in a manner that provides the degrees of freedom for the standard model on one hand and 2048 fermionic degrees of freedom for dark matter, corresponding to a ∼2 keV particle mass, on the other. In this context, we discuss the theoretical implications and the observable predictions.

Correlated gravitational wave and microlensing signals of macroscopic dark matter

Fermion dark matter particles can aggregate to form extended dark matter structures via a first-order phase transition in which the particles get trapped in the false vacuum. We study Fermi balls created in a phase transition induced by a generic quartic thermal effective potential. We show that for Fermi balls of mass, 3 × 10−12M⊙ ≲ MFB ≲ 10−5M⊙, correlated observations of gravitational waves produced during the phase transition (at SKA/THEIA/μAres), and gravitational microlensing caused by Fermi balls (at Subaru-HSC), can be made.

Possible nature of dark matter

We present a study of neutron star models that contain dark matter (DM) in the core. The DM is assumed to have a particle nature and to be self-interacting. Using constraints on the mass and radius of neutron stars, we investigate the allowed properties of either bosonic or fermionic DM particles. We consider cases where it constitutes up to 15% of the mass of the star, even though conventional mechanisms cannot generate such large fractions. For this purpose three different models of neutron stars are considered, the first involving nucleons only, the second including hyperons, and the last involving strange matter in the core. Different EoSs are constructed for the various cases of fermionic and bosonic DM. These EoSs are solved for selected properties of the DM particles and the results are tested against mass, radius and tidal deformability constraints for neutron stars. The distribution of energy density of DM and ordinary matter inside the neutron stars is also presented. It is found that if the DM is fermionic in nature it does not just sit in the core but it is present everywhere in the star, from the centre to outside the surface and may even envelop it.

Light Dirac neutrino portal dark matter with observable ΔN eff

We propose a Dirac neutrino portal dark matter scenarioby minimally extending the particle content of the Standard Model(SM) with three right-handed neutrinos (ν R ), a Dirac fermiondark matter candidate (ψ) and a complex scalar (ϕ), allof which are singlets under the SM gauge group. An additional ℤ4symmetry has been introduced for the stability of dark mattercandidate ψ and also ensuring the Dirac nature of lightneutrinos at the same time. Both the right handed neutrinos andthe dark matter thermalise with the SM plasma due to a new Yukawainteraction involving ν R , ψ and ϕ while the lattermaintains thermal contact via the Higgs portal interaction.The decoupling of ν R occurs when ϕloses its kinetic equilibrium with the SM plasma and thereafterall three ℤ4 charged particles form an equilibriumamong themselves with a temperature TνR .The dark matter candidate ψ finally freezes out within the darksector and preserves its relic abundance. We have found that in thepresent scenario, some portion of low mass dark matter (M ψ ≲ 10 GeV)is already excluded by the Planck 2018 data for keeping ν R sin the thermal bath below a temperature of 600 MeV and therebyproducing an excess contribution to N eff. The nextgeneration experiments like CMB-S4, SPT-3G etc. will have the required sensitivities to probe the entiremodel parameter space of this minimal scenario,especially the low mass range of ψ where direct detectionexperiments are still not capable enough for detection.

Strongly-interacting ultralight millicharged particles

We consider the implications of an ultra-light fermionic dark matter candidate that carries baryon number. This naturally arises if dark matter has a small charge under standard model baryon number whilst having an asymmetry equal and opposite to that in the visible universe. A prototypical model is a theory of dark baryons of a non-Abelian gauge group, i.e., a dark Quantum Chromo-Dynamics (QCD). For sub-eV dark baryon masses, the inner region of dark matter halos is naturally at ‘nuclear density’, allowing for the formation of exotic states of matter, akin to neutron stars. The Tremaine-Gunn lower bound on the mass of fermionic dark matter, i.e., the dark baryons, is violated by the strong short-range self-interactions, cooling via emission of light dark pions, and the Cooper pairing of dark quarks that occurs at densities that are high relative to the (ultra-low) dark QCD scale. We develop the astrophysics of these STrongly-interacting Ultra-light Millicharged Particles (STUMPs) utilizing the equation of state of dense quark matter, and find halo cores consistent with observations of dwarf galaxies. These cores are prevented from core-collapse by pressure of the ‘neutron star’, which suggests ultra-light dark QCD as a resolution to core-cusp problem of collisionless cold dark matter. The model is distinguished from ultra-light bosonic dark matter through direct detection and collider signatures, as well as by phenomena associated with superconductivity, such as Andreev reflection and superconducting vortices.

Exploring dark sector parameters in light of neutron star temperatures

Using neutron stars (NS) as a dark matter (DM) probe has gained broad attention recently, either from heating due to DM annihilation or its stability under the presence of DM. In this work, we investigate spin-$1/2$ fermionic DM $\chi$ charged under the $U(1)_{X}$ in the dark sector. The massive gauge boson $V$ of $U(1)_{X}$ gauge group can be produced in NS via DM annihilation. The produced gauge boson can decay into Standard Model (SM) particles before it exits the NS, despite its tiny couplings to SM particles. Thus, we perform a systematic study on $\chi\bar{\chi}\to2V\to4{\rm SM}$ as a new heating mechanism for NS in addition to $\chi\bar{\chi}\to2{\rm SM}$ and kinetic heating from DM-baryon scattering. The self-trapping due to $\chi V$ scattering is also considered. We assume the general framework that both kinetic and mass mixing terms between $V$ and SM gauge bosons are present. This allows both vector and axial-vector couplings between $V$ and SM fermions even for $m_V\ll m_Z$. Notably, the contribution from axial-vector coupling is not negligible when particles scatter relativistically. We point out that the above approaches to DM-induced NS heating are not yet adopted in recent analyses. Detectabilities of the aforementioned effects to the NS surface temperature by the future telescopes are discussed as well.

Double type-II Dirac seesaw accompanied by Dirac fermionic dark matter

A TeV-scale Higgs doublet with a small mixing to the standard model Higgs doublet can have the sizable Yukawa couplings to several right-handed neutrinos and the standard model lepton doublets. This provides a testable Dirac neutrino mass generation. We further consider a seesaw mechanism involving a U(1)B−L gauge symmetry, which predicts the existence of two right-handed neutrinos and a stable Dirac fermionic dark matter, to simultaneously explain the small mixing between the two Higgs doublets and the generation of the cosmic baryon asymmetry.

Decaying fermionic warm dark matter and XENON1T electronic recoil excess

In the light of the recently observed XENON1T electronic recoil (ER) data, we investigate the possibility of constraining the parameter space of a generic fermionic warm dark matter (WDM), decaying into a standard model (SM) neutrino and a photon. The photon as a decay product, when produced inside the XENON1T chamber, interacts with an electron of a xenon (Xe) atom, leading to a contribution in the observed ER data. We add this dark matter (DM) induced signal over the standard background ($\rm B_0$) considered by the XENON1T collaboration and perform a $\chi^2$ fit against the XENON1T data to obtain the best-fit values of the DM decay width and the associated $95\%$ confidence level (C.L.) band for DM mass ($m_\chi$) varied in the range $2 - 60$ keV. Additionally, we have extended our analysis by including two other background models available in the literature and in each case, the corresponding limits on the DM decay width are estimated for DM mass ($m_\chi$) in the domain $2 - 18$ keV. By comparing the constraints, obtained by fitting the XENON1T data, with the upper limits arising from various existing astrophysical and cosmological observations, we find that, for the background model $\rm B_0$, a fair amount of the DM parameter space is allowed at $95\%$ C.L. for DM masses outside the range $3.5\,{\rm keV} \lesssim m_\chi \lesssim 8.5\,{\rm keV}$. However, in case of other two background models, reasonable parts of the DM parameter space are favoured at $95\%$ C.L. by all astrophysical data for all DM masses in the range $2 - 18$ keV.

Complementarity between dark matter direct searches and CE\u03bdNS experiments in U(1)\u2032 models

We explore the possibility of having a fermionic dark matter candidate within U(1)′ models for CEνNS experiments in light of the latest COHERENT data and the current and future dark matter direct detection experiments. A vector-like fermionic dark matter has been introduced which is charged under U(1)′ symmetry, naturally stable after spontaneous symmetry breaking. We perform a complementary investigation using CEνNS experiments and dark matter direct detection searches to explore dark matter as well as Z′ boson parameter space. Depending on numerous other constraints arising from the beam dump, LHCb, BABAR, and the forthcoming reactor experiment proposed by the SBC collaboration, we explore the allowed region of Z′ portal dark matter.

Feeble DM-SM interaction via new scalar and vector mediators in rotating neutron stars

We investigate the possible presence of dark matter (DM) in massive and rotating neutron stars (NSs). For the purpose we extend our previous work [1] to introduce a light new physics vector mediator besides a scalar one in order to ensure feeble interaction between fermionic DM and β stable hadronic matter in NSs. The chosen masses of DM fermion and the mediators and the couplings are consistent with the self-interaction constraint from Bullet cluster and from present day relic abundance. Assuming that both the scalar and vector mediators contribute equally to the relic abundance, we compute the equation of state (EoS) of the DM admixed NSs to find that the present consideration of the vector new physics mediator do not bring any significant change to the EoS and static NS properties of DM admixed NSs compared to the case where only the scalar mediator was considered [1]. However, the obtained structural properties in static conditions are in good agreement with the various constraints on them from massive pulsars like PSR J0348+0432 and PSR J0740+6620, the gravitational wave (GW170817) data and the recently obtained results of NICER experiments for PSR J0030+0451 and PSR J0740+6620. We also extend our work to compute the rotational properties of DM admixed NSs rotating at different angular velocities. The present results in this regard suggest that the secondary component of GW190814 may be a rapidly rotating massive DM admixed NS. The constraints on rotational frequency from pulsars like PSR B1937+21 and PSR J1748-2446ad are also satisfied by our present results. Also, the constraints on moment of inertia are satisfied considering slow rotation. The universality relation in terms of normalized moment of inertia also holds good with our DM admixed EoS.

Testing freeze-in with axial and vector Z\u2032 bosons

The freeze-in production of Feebly Interacting Massive Particle (FIMP) dark matter in the early universe is an appealing alternative to the well-known — and constrained — Weakly Interacting Massive Particle (WIMP) paradigm. Although challenging, the phenomenology of FIMP dark matter has been receiving growing attention and is possible in a few scenarios. In this work, we contribute to this endeavor by considering a Z′ portal to fermionic dark matter, with the Z′ having both vector and axial couplings and a mass ranging from MeV up to PeV. We evaluate the bounds on both freeze-in and freeze-out from direct detection, atomic parity violation, leptonic anomalous magnetic moments, neutrino-electron scattering, collider, and beam dump experiments. We show that FIMPs can already be tested by most of these experiments in a complementary way, whereas WIMPs are especially viable in the Z′ low mass regime, in addition to the Z′ resonance region. We also discuss the role of the axial couplings of Z′ in our results. We therefore hope to motivate specific realizations of this model in the context of FIMPs, as well as searches for these elusive dark matter candidates.

Implication of J/ψ→(γ+)invisible for the effective field theories of neutrino and dark matter

We study the implication of $J/\psi$ decay into invisible particles for light sterile neutrino and sub-GeV dark matter (DM). The low-energy effective field theories (EFTs) are used for the description of general neutrino interactions and the Dirac fermion DM coupled to charm quark. For $J/\psi\to \gamma+{\rm invisible}$, we perform the likelihood fits for the individual neutrino and DM operators with distinct Lorentz structures and photon spectra. The limits on the decay branching fractions are obtained for different neutrino or DM scenarios and then converted to the lower bounds on the new energy scales. The most stringent bounds on the energy scale in neutrino and DM EFTs are 12.8 GeV and 11.6 GeV, respectively. The purely invisible decay $J/\psi\to {\rm invisible}$ provides complementary constraints on the effective operators. The relevant bound on the energy scale is above 100 GeV for the dipole operators. We also evaluate the limit on the DM-nucleon scattering cross section converted from $J/\psi$ data. The data of $J/\psi$ invisible decays are sensitive to the light DM mass range where the DM direct detection experiments cannot probe yet. The future Super Tau Charm Factory after one year run can push the limits down by two orders of magnitude.