Boosted Dark Matter Research Articles

Probing energetic light dark matter with multi-particle tracks signatures at DUNE

The search for relativistic scattering signals of cosmogenic light dark matter at terrestrial detectors has received increasing attention as an alternative approach to probe dark-sector physics. Large-volume neutrino experiments are well motivated for searches of dark matter that interacts very weakly with Standard Model particles and/or that exhibits a small incoming flux. We perform a dedicated signal sensitivity study for a detector similar to the one proposed by the DUNE Collaboration for cosmogenic dark-matter signals resulting from a non-minimal multi-particle dark-sector scenario. The liquid argon time projection chamber technology adopted for the DUNE detectors is particularly suited for searching for complicated signatures owing to good measurement resolution and particle identification, as well as dE/dx measurements to recognize merged tracks. Taking inelastic boosted dark matter as our benchmark scenario that allows for multiple visible particles in the final state, we demonstrate that the DUNE far detectors have a great potential for probing scattering signals induced by relativistic light dark matter. Detector effects and backgrounds have been estimated and taken into account. Model-dependent and model-independent expected sensitivity limits for a DUNE-like detector are presented.

Leptonic new force and cosmic-ray boosted dark matter for the XENON1T excess

The recently reported excess in XENON1T is explained by new leptonic forces, which are free from gauge anomalies. We focus on two scenarios with and without dark matter. In Scenario #1, the gauge boson of gauged lepton number U(1)Le−Lj, j=μ or τ provides non-standard interaction between solar neutrino and electron that enhances the number of electron recoil events in the XENON1T detector. In Scenarino #2, the new gauge boson exclusively couples to electron and dark matter, then cosmic-ray electrons can transfer their momenta to dark matter in halo. The boosted dark matter generates the electron recoil signals of O(1) keV. The dark matter, aided by the new gauge interaction, efficiently heats up a neutron star in our Galaxy more than ∼1500 K as a neutron star captures the halo dark matter. Therefore, we propose to utilize the future infrared telescope to test our scenario.

Boosted Dark Matter Interpretation of the XENON1T Excess.

We propose boosted dark matter (BDM) as a possible explanation for the excess of keV electron recoil events observed by XENON1T. BDM particles have velocities much larger than those typical of virialized dark matter, and, as such, BDM-electron scattering can naturally produce keV electron recoils. We show that the required BDM-electron scattering cross sections can be easily realized in a simple model with a heavy vector mediator. Though these cross sections are too large for BDM to escape from the Sun, the BDM flux can originate from the Galactic Center or from halo dark matter annihilations. Furthermore, a daily modulation of the BDM signal will be present, which could not only be used to differentiate it from various backgrounds but would also provide important directional information for the BDM flux.

Optimizing energetic light dark matter searches in dark matter and neutrino experiments

Neutrino and dark matter experiments with large-volume ( underset{sim }{>} ,2 1 ton) detectors can provide excellent sensitivity to signals induced by energetic light dark matter coming from the present universe. Taking boosted dark matter as a concrete example of energetic light dark matter, we scrutinize two representative search channels, electron scattering and proton scattering including deep inelastic scattering processes, in the context of elastic and inelastic boosted dark matter, in a completely detector-independent manner. In this work, a dark gauge boson is adopted as the particle to mediate the interactions between the Standard Model particles and boosted dark matter. We find that the signal sensitivity of the two channels highly depends on the (mass-)parameter region to probe, so search strategies and channels should be designed sensibly especially at the earlier stage of experiments. In particular, the contribution from the boosted-dark-matter-initiated deep inelastic scattering can be subleading (important) compared to the quasi-elastic proton scattering, if the mass of the mediator is below (above) mathcal{O} (GeV). We demonstrate how to practically perform searches and relevant analyses, employing example detectors such as DarkSide-20k, DUNE, Hyper-Kamiokande, and DeepCore, with their respective detector specifications taken into consideration. For other potential detectors we provide a summary table, collecting relevant information, from which similar studies can be fulfilled readily.

Thermodynamic evolution of secluded vector dark matter: conventional WIMPs and nonconventional WIMPs

The secluded dark matter resides within a hidden sector and self-annihilates into lighter mediators which subsequently decay to the Standard Model (SM) particles. Depending on the coupling strength of the mediator to the SM, the hidden sector can be kinetically decoupled from the SM bath when the temperature drops below the mediator’s mass, and the dark matter annihilation cross section at freeze-out is thus possible to be boosted above the conventional value of weak interacting massive particles. We present a comprehensive study on thermodynamic evolution of the hidden sector from the first principle, using the simplest secluded vector dark matter model. Motivated by the observation of Galactic center gamma-ray excess, we take two mass sets ∼ mathcal{O} (80 GeV) for the dark matter and mediator as examples to illustrate the thermodynamics. The coupled Boltzmann moment equations for number densities and temperature evolutions of the hidden sector are numerically solved. The formalism can be easily extended to a general secluded dark matter model. We show that a long-lived mediator can result in a boosted dark matter annihilation cross section to account for the relic abundance. We further show the parameter space which provides a good fit to the Galactic center excess data and is compatible with the current bounds and LUX-ZEPLIN projected sensitivity. We find that the future observations of dwarf spheroidal galaxies offer promising reach to probe the most relic allowed parameter space relevant to the boosted dark matter annihilation cross section.

Explaining the ANITA anomaly with inelastic boosted dark matter

We propose a new physics scenario in which the decay of a very heavy dark-matter candidate which does not interact with the neutrino sector could explain the two anomalous events recently reported by ANITA. The model is composed of two components of dark matter, an unstable dark-sector state, and a massive dark gauge boson. We assume that the heavier dark-matter particle of EeV-range mass is distributed over the galactic halo and disintegrates into a pair of lighter -- highly boosted -- dark-matter states in the present universe which reach and penetrate the Earth. The latter scatters {\it in}elastically off a nucleon and produces a heavier dark-sector unstable state which subsequently decays back to the lighter dark matter along with hadrons, which induce Extensive Air Showers, via on-/off-shell dark gauge boson. Depending on the mass hierarchy within the dark sector, either the dark gauge boson or the unstable dark-sector particle can be long-lived, hence transmitted significantly through the Earth. We study the angular distribution of the signal and show that our model favors emergence angles in the range $\sim 25^\circ -35^\circ$ if the associated parameter choices bear the situation where the mean free path of the boosted incident particle is much larger than the Earth diameter while its long-lived decay product has a decay length of dimensions comparable to the Earth radius. Our model, in particular, avoids any constraints from complementary neutrino searches such as IceCube or the Auger observatory.

Searching for boosted dark matter via dark-photon bremsstrahlung

We propose a new search channel for boosted dark matter (BDM) signals coming from the present universe, which are distinct from simple neutrino signals including those coming from the decay or pair-annihilation of dark matter. The signal process is initiated by the scattering of high-energetic BDM off either an electron or a nucleon. If the dark matter is dark-sector U(1)-charged, the scattered BDM may radiate a dark gauge boson (called "dark-strahlung") which subsequently decays to a Standard Model fermion pair. We point out that the existence of this channel may allow for the interpretation that the associated signal stems from BDM, not from the dark-matter-origin neutrinos. Although the dark-strahlung process is generally subleading compared to the lowest-order simple elastic scattering of BDM, we find that the BDM with a significant boost factor may induce an O(10-20%) event rate in the parameter regions unreachable by typical beam-produced dark-matter. We further find that the dark-strahlung channel may even outperform the leading-order channel in the search for BDM, especially when the latter is plagued by substantial background contamination. We argue that cosmogenic BDM searches readily fall in such a case, hence taking full advantage of dark-strahlung. As a practical application, experimental sensitivities expected in the leading-order and dark-strahlung channels are contrasted in dark gauge boson parameter space, under the environment of DUNE far-detectors, revealing usefulness of dark-strahlung.

Monochromatic dark neutrinos and boosted dark matter in noble liquid direct detection

If dark matter self-annihilates into neutrinos or a second component of ("boosted") dark matter that is nucleophilic, the annihilation products may be detected with high rates via coherent nuclear scattering. A future multi-ten-tonne liquid xenon detector such as DARWIN, and a multi-hundred-tonne liquid argon detector, ARGO, would be sensitive to the flux of these particles in complementary ranges of $10-1000$ MeV dark matter masses. We derive these sensitivities after accounting for atmospheric and diffuse supernova neutrino backgrounds, and realistic nuclear recoil acceptances. We find that their constraints on the dark neutrino flux may surpass neutrino detectors such as Super-Kamiokande, and that they would extensively probe parametric regions that explain the missing satellites problem in neutrino portal models. The XENON1T and Borexino experiments currently restrict the effective baryonic coupling of thermal boosted dark matter to $\lesssim 10-100 \ \times$ the weak interaction, but DARWIN and ARGO would probe down to couplings 10 times smaller. Detection of boosted dark matter with baryonic couplings $\sim 10^{-3}-10^{-2} \ \times$ the weak coupling could indicate that the dark matter density profile in the centers of galactic halos become cored, rather than cuspy, through annihilations. This work demonstrates that, alongside liquid xenon, liquid argon direct detection technology would emerge a major player in dark matter searches within and beyond the WIMP paradigm.

First Direct Search for Inelastic Boosted Dark Matter with COSINE-100.

A search for inelastic boosted dark matter (IBDM) using the COSINE-100 detector with 59.5days of data is presented. This relativistic dark matter is theorized to interact with the target material through inelastic scattering with electrons, creating a heavier state that subsequently produces standard model particles, such as an electron-positron pair. In this study, we search for this electron-positron pair in coincidence with the initially scattered electron as a signature for an IBDM interaction. No excess over the predicted background event rate is observed. Therefore, we present limits on IBDM interactions under various hypotheses, one of which allows us to explore an area of the dark photon parameter space that has not yet been covered by other experiments. This is the first experimental search for IBDM using a terrestrial detector.

Searching for boosted dark matter at ProtoDUNE

We propose the first experimental test of the inelastic boosted dark matter hypothesis, capitalizing on the new physics potential with the imminent data taking of the ProtoDUNE detectors. More specifically, we explore various experimental signatures at the cosmic frontier, arising in boosted dark matter scenarios, i.e., relativistic, inelastic scattering of boosted dark matter often created by the annihilation of its heavier component which usually comprises of the dominant relic abundance. Although features are unique enough to isolate signal events from potential backgrounds, vetoing a vast amount of cosmic background is rather challenging as the detectors are located on the ground. We argue, with a careful estimate, that such backgrounds nevertheless can be well under control by performing dedicated analyses after data acquisition. We then discuss some phenomenological studies which can be achieved with ProtoDUNE, employing a dark photon scenario as our benchmark dark-sector model.

Boosted self-interacting dark matter in a multi-component dark matter model

In models of multi-component dark matter, the lighter component of dark matter can be boosted by annihilations of the heavier state if mass splitting is large enough. Such relativistic dark matter can be detectable via large neutrino detectors such as Super-Kamiokande and IceCube. Moreover, if the process is inelastic scattering and decay length of the produced particle is short enough, another signature coming from the decay can also be detectable. In this paper, we construct a simple two-component dark matter model with a hidden U(1)D gauge symmetry where the lighter component of dark matter has a potential to improve the so-called small scale structure problems with large self-interacting cross section. We estimate number of multi-Cherenkov ring events due to both of the boosted dark matter and subsequent decay of the particle produced by inelastic scattering at Hyper-Kamiokande future experiment. Some relevant constraints, such as dark matter direct detection and cosmological observations, are also taken into account. The numerical analysis shows that some parameter space which can induce large self-interacting cross section can give a few multi-Cherenkov ring events per year at Hyper-Kamiokande.

Boosted dark matter quarrying at surface neutrino detectors

We propose the idea of “Earth Shielding” to reject cosmic-ray backgrounds, in the search for boosted dark matter at surface neutrino detectors, resulting in the enhancement of the signal-to-background ratio. The identification of cosmic-originating rare signals, especially lacking features, at surface detectors is often considered hopeless due to a vast amount of cosmic-ray-induced background, hence underground experiments are better motivated to avoid such a challenge. We claim that surface detectors can attain remarkable sensitivities to even featureless signals, once restricting to events coming through the Earth from the opposite side of the detector location for the signals leaving appreciable tracks from which the source direction is inferred. By doing so, potential backgrounds in the signal region of interest can be substantially suppressed. To validate our claim, we study experimental reaches at several surface experiments such as SBN Program (MicroBooNE, ICARUS, and SBND) and ProtoDUNE for elastic boosted dark matter signatures stemming from the Galactic Center. We provide a systematic discussion on maximizing associated signal sensitivities.

Search for Boosted Dark Matter Interacting with Electrons in Super-Kamiokande.

A search for boosted dark matter using 161.9kt yr of Super-Kamiokande IV data is presented. We search for an excess of elastically scattered electrons above the atmospheric neutrino background, with a visible energy between 100MeV and 1TeV, pointing back to the Galactic center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic center and Sun are calculated. Limits are also calculated for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay. This is the first experimental search for boosted dark matter from the Galactic center or the Sun interacting in a terrestrial detector.

Non-minimal dark matter search in dark matter colliders

In the scenarios of dark matter (DM) with a non-minimal dark sector, we revisit a new detection strategy of observing two or three simultaneous signals from inelastic scattering of a boosted DM [1]. The relativistically incoming DM can scatter off inelastically to a heavier unstable dark sector particle which decays back in to the DM associated with visible Standard Model particles inside large volume neutrino detectors. The existence of the secondary procedure renders us to separate it from conventional neutrino scattering background. The relativistically incoming DM can come from the universe by the annihilation of heavy DM component in an inelastic boosted DM scenario or produced by the beam bombardments in fixed target experiments.

Boosted dark matter and its implications for the features in IceCube HESE data

We study the implications of the premise that any new, relativistic, highly energetic neutral particle that interacts with quarks and gluons would create cascade-like events in the IceCube (IC) detector. Such events would be observationally indistinguishable from neutral current deep-inelastic (DIS) scattering events due to neutrinos. Consequently, one reason for deviations, breaks or excesses in the expected astrophysical power-law neutrino spectrum could be the flux of such a particle. Motivated by features in the recent 1347-day IceCube high energy starting event (HESE) data, we focus on particular boosted dark matter (χ) related realizations of this premise. Here, χ is assumed to be much lighter than, and the result of, the slow decay of a massive scalar (ϕ ) which constitutes a major fraction of the Universe's dark matter (DM) . We show that this hypothesis, coupled with a standard power-law astrophysical neutrino flux is capable of providing very good fits to the present data, along with a possible explanation of other features in the HESE sample. These features include a) the paucity of events beyond ∼ 2 PeV b) a spectral feature resembling a dip or a spectral change in the 400 TeV–1 PeV region and c) an excess in the 50−100 TeV region. We consider two different boosted DM scenarios, and determine the allowed mass ranges and couplings for four different types of mediators (scalar, pseudoscalar, vector and axial-vector) which could connect the standard and dark sectors.We consider constraints from gamma-ray observations and collider searches. We find that the gamma-ray observations provide the most restrictive constraints, disfavouring the 1σ allowed parameter space from IC fits, while still being consistent with the 3σ allowed region. We also test our proposal and its implications against the (statistically independent) sample of six year through-going muon track data recently released by IceCube.

Phases of cannibal dark matter

A hidden sector with a mass gap undergoes an epoch of cannibalism if number changing interactions are active when the temperature drops below the mass of the lightest hidden particle. During cannibalism, the hidden sector temperature decreases only logarithmically with the scale factor. We consider the possibility that dark matter resides in a hidden sector that underwent cannibalism, and has relic density set by the freeze-out of two-to-two annihilations. We identify three novel phases, depending on the behavior of the hidden sector when dark matter freezes out. During the cannibal phase, dark matter annihilations decouple while the hidden sector is cannibalizing. During the chemical phase, only two-to-two interactions are active and the total number of hidden particles is conserved. During the one way phase, the dark matter annihilation products decay out of equilibrium, suppressing the production of dark matter from inverse annihilations. We map out the distinct phenomenology of each phase, which includes a boosted dark matter annihilation rate, new relativistic degrees of freedom, warm dark matter, and observable distortions to the spectrum of the cosmic microwave background.

(In)Direct detection of boosted dark matter

We present a new multi-component dark matter model with a novel experimental signature that mimics neutral current interactions at neutrino detectors. In our model, the dark matter is composed of two particles, a heavier dominant component that annihilates to produce a boosted lighter component that we refer to as boosted dark matter. The lighter component is relativistic and scatters off electrons in neutrino experiments to produce Cherenkov light. This model combines the indirect detection of the dominant component with the direct detection of the boosted dark matter. Directionality can be used to distinguish the dark matter signal from the atmospheric neutrino background. We discuss the viable region of parameter space in current and future experiments.

Boosted dark matter in IceCube and at the galactic center

We show that the event excess observed by the IceCube collaboration at TeV--PeV energies, usually interpreted as evidence for astrophysical neutrinos, can be explained alternatively by the scattering of highly boosted dark matter particles. Specifically, we consider a scenario where a $\sim 4$ PeV scalar dark matter particle $\phi$ can decay to a much lighter dark fermion $\chi$, which in turn scatters off nuclei in the IceCube detector. Besides these events, which are exclusively shower-like, the model also predicts a secondary population of events at $\mathcal{O}(100 \text{TeV})$ originating from the 3-body decay $\phi \to \chi \bar\chi a$, where $a$ is a pseudoscalar which mediates dark matter--Standard Model interactions and whose decay products include neutrinos. This secondary population also includes track-like events, and both populations together provide an excellent fit to the IceCube data. We then argue that a relic abundance of light Dark Matter particles $\chi$, which may constitute a subdominant component of the Dark Matter in the Universe, can have exactly the right properties to explain the observed excess in GeV gamma rays from the galactic center region. Our boosted Dark Matter scenario also predicts fluxes of $\mathcal{O}(10)$ TeV positrons and $\mathcal{O}(100 \text{TeV})$ photons from 3-body cascade decays of the heavy Dark Matter particle $\phi$, and we show how these can be used to constrain parts of the viable parameter space of the model. Direct detection limits are weak due to the pseudoscalar couplings of $\chi$. Accelerator constraints on the pseudoscalar mediator $a$ lead to the conclusion that the preferred mass of $a$ is $\gtrsim 10$ GeV and that large coupling to $b$ quarks but suppressed or vanishing coupling to leptons are preferred.

Boosted dark matter signals uplifted with self-interaction

We explore detection prospects of a non-standard dark sector in the context of boosted dark matter. We focus on a scenario with two dark matter particles of a large mass difference, where the heavier candidate is secluded and interacts with the standard model particles only at loops, escaping existing direct and indirect detection bounds. Yet its pair annihilation in the galactic center or in the Sun may produce boosted stable particles, which could be detected as visible Cherenkov light in large volume neutrino detectors. In such models with multiple candidates, self-interaction of dark matter particles is naturally utilized in the assisted freeze-out mechanism and is corroborated by various cosmological studies such as N-body simulations of structure formation, observations of dwarf galaxies, and the small scale problem. We show that self-interaction of the secluded (heavier) dark matter greatly enhances the capture rate in the Sun and results in promising signals at current and future experiments. We perform a detailed analysis of the boosted dark matter events for Super-Kamiokande, Hyper-Kamiokande and PINGU, including notable effects such as evaporation due to self-interaction and energy loss in the Sun.

Detecting boosted dark matter from the Sun with large volume neutrino detectors

We study novel scenarios where thermal dark matter (DM) can be efficiently captured in the Sun and annihilate into boosted dark matter. In models with semi-annihilating DM, where DM has a non-minimal stabilization symmetry, or in models with a multi-component DM sector, annihilations of DM can give rise to stable dark sector particles with moderate Lorentz boosts. We investigate both of these possibilities, presenting concrete models as proofs of concept. Both scenarios can yield viable thermal relic DM with masses O(1)-O(100) GeV. Taking advantage of the energetic proton recoils that arise when the boosted DM scatters off matter, we propose a detection strategy which uses large volume terrestrial detectors, such as those designed to detect neutrinos or proton decays. In particular, we propose a search for proton tracks pointing towards the Sun. We focus on signals at Cherenkov-radiation-based detectors such as Super-Kamiokande (SK) and its upgrade Hyper-Kamiokande (HK). We find that with spin-dependent scattering as the dominant DM-nucleus interaction at low energies, boosted DM can leave detectable signals at SK or HK, with sensitivity comparable to DM direct detection experiments while being consistent with current constraints. Our study provides a new search path for DM sectors with non-minimal structure.