WIMPs Research Articles

Z-Portal Continuum Dark Matter.

We examine the possibility that dark matter (DM) consists of a gapped continuum, rather than ordinary particles. A weakly interacting continuum (WIC) model, coupled to the standard model via a Z portal, provides an explicit realization of this idea. The thermal DM relic density in this model is naturally consistent with observations, providing a continuum counterpart of the "WIMP miracle." Direct detection cross sections are strongly suppressed compared to ordinary Z-portal WIMP, thanks to a unique effect of the continuum kinematics. Continuum DM states decay throughout the history of the Universe, and observations of cosmic microwave background place constraints on potential late decays. Production of WICs at colliders can provide a striking cascade-decay signature. We show that a simple Z-portal WIC model provides a fully viable DM candidate consistent with all current experimental constraints.

Searching for low-mass dark matter via the Migdal effect in COSINE-100

We report on the search for weakly interacting massive particle (WIMP) dark matter candidates in the galactic halo that interact with sodium and iodine nuclei in the COSINE-100 experiment and produce energetic electrons that accompany recoil nuclei via the the Migdal effect. The WIMP mass sensitivity of previous COSINE-100 searches that relied on the detection of ionization signals produced by target nuclei recoiling from elastic WIMP-nucleus scattering was restricted to WIMP masses above $\sim$5 GeV/$c^2$ by the detectors' 1 keVee energy-electron-equivalent threshold. The search reported here looks for recoil signals enhanced by the Migdal electrons that are ejected during the scattering process. This is particularly effective for the detection of low-mass WIMP scattering from the crystals' sodium nuclei in which a relatively larger fraction of the WIMP's energy is transferred to the nucleus recoil energy and the excitation of its orbital electrons. In this analysis, the low-mass WIMP search window of the COSINE-100 experiment is extended to WIMP mass down to 200 MeV/$c^2$. The low-mass WIMP sensitivity will be further improved by lowering the analysis threshold based on a multivariable analysis technique. We consider the influence of these improvements and recent developments in detector performance to re-evaluate sensitivities for the future COSINE-200 experiment. With a 0.2 keVee analysis threshold and high light-yield NaI(Tl) detectors (22 photoelectrons/keVee), the COSINE-200 experiment can explore low-mass WIMPs down to 20 MeV/$c^2$ and probe previously unexplored regions of parameter space.

White Dwarfs as Physics Laboratories: Lights and Shadows

The evolution of white dwarfs is essentially a gravothermal process of cooling in which the basic ingredients for predicting their evolution are well identified, although not always well understood. There are two independent ways to test the cooling rate. One is the luminosity function of the white dwarf population, and another is the secular drift of the period of pulsation of those individuals that experience variations. Both scenarios are sensitive to the cooling or heating time scales, for which reason, the inclusion of any additional source or sink of energy will modify these properties and will allow to set bounds to these perturbations. These studies also require complete and statistical significant samples for which current large data surveys are providing an unprecedented wealth of information. In this paper we review how these techniques are applied to several cases like the secular drift of the Newton gravitational constant, neutrino magnetic moments, axions and weakly interacting massive particles (WIMPS).

The Outreach and Education program of the Darkside experiment

The Darkside experiment aims at the direct detection of Dark Matter in the form of Weakly Interacting Massive Particles (WIMPs). It is a 20-tonne (fiducial) argon dual-phase Time-Projection Chamber (TPC) that exploits the cryogenic SiPM technology to identify unambiguously the nuclear recoils induced by WIMPs. The experiment is being installed at the INFN Gran Sasso National Laboratories, in Italy, and will start operation around 2024. The goal of the Outreach and Education program of DarkSide is to disseminate the experiment activity through promotional videos and events addressed to the general public and students. One of our main activities is the DarkSide Masterclass, in which high school students become physicists for a day searching for WIMPs. After a few introductory lectures, the students analyze real data from the precursor DarkSide-50 experiment. Master degree students have access to a more complex version of this Masterclass. Six Masterclass events took place in the last two years, with the participation reaching 400 students in one event. In this talk, we will present the detailed Outreach and Education program of Darkside Collaboration.

Indirect Dark Matter search towards the Sun with the ANTARES neutrino telescope

Dark Matter particles, such as Weakly Interactive Massive Particles (WIMPs) gravitationally captured in massive celestial objects, can be indirectly detected through their annihilation into Standard Model particles. The centres of those massive objects are, therefore, places where to look for a possible high energy neutrino flux excess from dark matter annihilations, using neutrino telescopes. The deep-sea neutrino telescope ANTARES, located in the Mediterranean Sea, has been shown to be very competitive in the quest for Dark Matter WIMPs produced in the Galactic Centre. A closer potential DM source is the Sun, where it is possible to have a very clean signal since the background from astrophysical origin is expected to be very low. In this work we show the expected sensitivity of a search for Dark Matter WIMPs from the Sun, using 13 years of data collected by ANTARES.

Search for dark matter signals toward the irregular dwarf galaxy WLM with H.E.S.S

Cosmological and astrophysical probes suggest that dark matter (DM) makes up for 85% of the total matter of the Universe. The determination of its nature, however, remains one of the greatest challenges of fundamental Physics. In the DM indirect detection framework, Weakly Interacting Massive Particles (WIMPs) particles would produce signals by self-annihilating and creating SM products such as γ rays, which might be detected by ground-based telescopes. Dwarf irregular galaxies represent promising targets for the search for DM as they are assumed to be dark matter dominated. These dwarf irregular galaxies are rotationally supported with relatively simple and well measured kinematics which lead to small uncertainties on their dark matter distribution profiles. In 2018, the H.E.S.S. telescopes observed the irregular dwarf galaxy Wolf-Lundmark-Melotte (WLM) for 18 hours. These observations are the very first ones made by an imaging air Cherenkov telescope toward this kind of objects. We search for a DM signal looking for excess of γ rays towards WLM dwarf galaxy. We perform the first analysis of this source in stereoscopy using the data taken by the five H.E.S.S. telescopes. In this proceeding, we present the new results on the observations of WLM interpreted in terms of velocity-weighted cross-section for DM self-annihilation 〈συ〉 as a function of DM particle mχ mass for the eight annihilation channels , and γγ.

Combined Dark Matter searches from dwarf spheroidal galaxies observations by Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS

Dwarf spheroidal galaxies (dSphs) are ideal targets for Dark Matter (DM) indirect searches due to their high DM content and their negligible expected astrophysical background. In this presentation, we report on the combined analysis of the observations of 20 dSphs by Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS collaborations in the search for DM, focusing on the Weakly Interacting Massive Particles (WIMPs) scenario. The combined analysis allows us to maximize the sensitivity by combining individual data sets from all five experiments for which the energy ranges of the search overlap. New constraints, spanning a range of DM masses from 5 GeV to 100 TeV, on the velocity-weighted cross section for DM self annihilation will be presented.

Scintillation light increase of carbontetrafluoride gas at low temperature

Scintillation detector is widely used for the particle detection in the field of particle physics. Particle detectors containing fluorine-19 (19F) are known to have advantages for Weakly Interacting Massive Particles (WIMPs) dark matter search, especially for spin-dependent interactions with WIMPs due to its spin structure. In this study, the scintillation properties of carbontetrafluoride (CF4) gas at low temperature were evaluated because its temperature dependence of light yield has not been measured. We evaluated the light yield by cooling the gas from room temperature (300 K) to 263 K. As a result, the light yield of CF4 was found to increase by (41.0 ± 4.0stat. ± 6.6syst.)% and the energy resolution was also found to improve at low temperature.

Projected sensitivities of the LUX-ZEPLIN experiment to new physics via low-energy electron recoils

LUX-ZEPLIN (LZ) is a dark matter detector expected to obtain world-leading sensitivity to weakly interacting massive particles (WIMPs) interacting via nuclear recoils with a ~7-tonne xenon target mass. This manuscript presents sensitivity projections to several low-energy signals of the complementary electron recoil signal type: 1) an effective neutrino magnetic moment and 2) an effective neutrino millicharge, both for pp-chain solar neutrinos, 3) an axion flux generated by the Sun, 4) axion-like particles forming the galactic dark matter, 5) hidden photons, 6) mirror dark matter, and 7) leptophilic dark matter. World-leading sensitivities are expected in each case, a result of the large 5.6t 1000d exposure and low expected rate of electron recoil backgrounds in the $<$100keV energy regime. A consistent signal generation, background model and profile-likelihood analysis framework is used throughout.

Search for dark matter from the centre of the Earth with 8 years of IceCube data

Neutrinos have been proved to be unique messengers in the understanding of fundamental physics processes, and in astrophysical data sets they may provide hints of physics beyond the Standard Model. For example, neutrinos could be the key to discerning between various dark matter models that are based on Weakly Interacting Massive Particles (WIMPs). WIMPs can scatter off standard matter nuclei in the vicinity of massive bodies such as the Sun or the Earth, lose velocity, and be gravitationally trapped in the center of the body. Self-annihilation of dark matter into Standard Model particles may produce an observable flux of neutrinos. For the case of the Earth, an excess of neutrinos coming from the center of the planet could indicate WIMP capture and annihilation at the Earth’s core. The IceCube Neutrino Observatory, located at the geographical South Pole, is sensitive to these excess neutrinos. A search has been conducted on 8 years of IceCube data, probing multiple dark matter channels and masses. With this analysis, we show that IceCube has world-leading sensitivity to the spin-independent dark matter-nucleon scattering cross section above a WIMP mass of 100 GeV.

Remarks on bosonic super-WIMP search experiments

Bosonic super--weakly interacting massive particles (WIMPs), including pseudoscalar and vector particles, are dark-matter candidates. To date, many underground experiments searches for super-WIMPs have been performed in the mass range of a few $\mathrm{keV}/{c}^{2}$ to $1\text{ }\text{ }\mathrm{MeV}/{c}^{2}$. All these searches utilize the absorption process of a super-WIMP by a target atom in the detector, which is similar to the photoelectric effect. We consider another process---namely, a Compton-like process. As an example, we compare the cross section of a germanium atom for the absorption process with that of a Compton-like process. Our findings indicate that the cross section for the Compton-like process becomes dominant relative to that for the absorption process for mass above approximately $150\text{ }\text{ }\mathrm{keV}/{c}^{2}$ for both pseudoscalar and vector super-WIMPs. In particular, the cross section for the Compton-like process for a vector super-WIMP becomes increasingly greater than that for the absorption process by 1 to 2 orders of magnitude in the $400\text{ }\text{ }\mathrm{keV}/{c}^{2}$ to $1\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ mass range, respectively. By including the Compton-like process, which has not been used in any other super-WIMP search experiments, the experimental upper limits can be improved.

CMB and 21-cm bounds on early structure formation boosted by primordial black hole entropy fluctuations

The dark matter (DM) can consist of the primordial black holes (PBHs) in addition to the conventional weakly interacting massive particles (WIMPs). The Poisson fluctuations of the PBH number density produce the isocurvature perturbations which can dominate the matter power spectrum at small scales and enhance the early structure formation. We study how the WIMP annihilation from those early formed structures can affect the CMB (in particular the E-mode polarization anisotropies and $y$-type spectral distortions) and global 21cm signals. Our studies would be of particular interest for the light (sub-GeV) WIMP scenarios which have been less explored compared with the mixed DM scenarios consisting of PBHs and heavy ($\gtrsim 1$ GeV) WIMPs. For instance, for the self-annihilating DM mass $m_{\chi}=1$ MeV and the thermally averaged annihilation cross section $\langle \sigma v \rangle \sim 10^{-30} \rm cm^3/s$, the latest Planck CMB data requires the PBH fraction with respect to the whole DM to be at most ${\cal O}(10^{-3})$ for the sub-solar mass PBHs and an even tighter bound (by a factor $\sim 5$) can be obtained from the global 21-cm measurements.

Phenomenology of nuclear scattering for a WIMP of arbitrary spin

We provide a first systematic and quantitative discussion of the phenomenology of the nonrelativistic effective Hamiltonian describing the nuclear scattering process for a weakly interacting massive particle (WIMP) of arbitrary spin ${j}_{\ensuremath{\chi}}$. To this aim we obtain constraints from a representative sample of present direct detection experiments assuming the WIMP-nucleus scattering process to be driven by each one of the 44 effective couplings that arise for ${j}_{\ensuremath{\chi}}\ensuremath{\le}2$. We find that a high value of the multipolarity $s\ensuremath{\le}2{j}_{\ensuremath{\chi}}$ of the coupling, related to the power of the momentum transfer $q$ appearing in the scattering amplitude, leads to a suppression of the expected rates and pushes the expected differential spectra to large recoil energies ${E}_{R}$. For $s\ensuremath{\le}4$ the effective scales probed by direct detection experiments can be suppressed by up to five orders of magnitude compared to the case of a standard spin-independent interaction. For operators with large $s$ the expected differential spectra can be pushed to recoil energies in the MeV range, with the largest part of the signal concentrated at ${E}_{R}\ensuremath{\gtrsim}100\text{ }\text{ }\mathrm{keV}$ and a peculiar structure of peaks and minima arising when both the nuclear target and the WIMPs are heavy. As a consequence the present bounds on the effective operators can be significantly improved by extending the recoil energy intervals to higher recoil energies. Our analysis assumes effective interaction operators that are irreducible under the rotation group. Such operators drive the interactions of high-multipole dark matter candidates, i.e., states that possess only the highest multipole allowed by their spin. As a consequence our analysis represents also the first phenomenological study of the direct detection of quadrupolar, octupolar, and hexadecapolar dark matter.

Leptophilic fermion WIMP: Role of future lepton colliders

The leptophilic weakly interacting massive particle (WIMP) is realized in a minimal renormalizable model scenario where scalar mediators with lepton number establish the WIMP interaction with the standard model (SM) leptons. We perform a comprehensive analysis for such a WIMP scenario for two distinct cases with an SU(2) doublet or singlet mediator considering all the relevant theoretical, cosmological and experimental constraints at present. We show that the mono-photon search at near-future lepton collider experiments (ILC, FCC-ee, CEPC, etc.) can play a significant role to probe the yet unexplored parameter range allowed by the WIMP relic density constraint. This will complement the search prospect at the near-future hadron collider experiment (HL-LHC). Furthermore, we discuss the combined model scenario including both the doublet and singlet mediator. The combined model is capable of explaining the long-standing muon (g-2) anomaly which is an additional advantage. We demonstrate that the allowed region for anomalous muon (g-2) explanation, which has been updated very recently at Fermi National Accelerator Laboratory, can also be probed at the future colliders which will thus be a simultaneous authentication of the model scenario.

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.

Indirect search for dark matter in the Galactic Centre with IceCube

Neutrino telescopes such as IceCube can be used to conduct indirect dark matter searches. A common assumption is that dark matter consists of Weakly Interacting Massive Particles (WIMPs), which are expected to produce Standard Model particles when they annihilate or decay. IceCube could then detect the neutrinos generated by these Standard Model particles. Since the Milky Way is expected to be immersed in a dark matter halo whose density increases towards its centre, the Galactic Centre is a designated target for indirect searches. In this contribution, we present the sensitivities of the search for dark matter in the Galactic Centre based on IceCube data, probing annihilation through νeν̅e, νμν̅μ, ντν̅τ, μ+μ-, τ+τ-, W+W- and bb̅. We demonstrate that between WIMP masses of 5 GeV to 1 TeV, the sensitivity of IceCube to the velocity-averaged WIMP self-annihilation cross-section improves by an order of magnitude over previous searches with IceCube and other neutrino telescopes.

A new way to test the WIMP dark matter models

In this paper, we investigate the possibility of testing the weakly interacting massive particle (WIMP) dark matter (DM) models by applying the simplest phenomenological model which introduces an interaction term between dark energy (DE) and WIMP DM, i.e., Q = 3γDMHρDM. In general, the coupling strength γDE is close to 0 as the interaction between DE and WIMP DM is very weak, thus the effect of γDE on the evolution of Y associated with DM energy density can be safely neglected. Meanwhile, our numerical calculation also indicates that xf ≈ 20 is associated with DM freeze-out temperature, which is the same as the vanishing interaction scenario. As for DM relic density, it will be magnified by frac{2-3{upgamma}_{mathrm{DM}}}{2}{left[2pi {g}_{ast }{m}_{mathrm{DM}}^3/left(45{s}_0{x}_f^3right)right]}^{gamma_{mathrm{DM}}} times, which provides a new way to test WIMP DM models. As an example, we analyze the case in which WIMP DM is a scalar DM. (SGL+SNe+Hz) and (CMB+BAO+SNe) cosmological observations will give γDM = {0.134}_{-0.069}^{+0.17} and γDM = −0.0008 ± 0.0016, respectively. After further considering the constraints from DM direct detection experiment, DM indirect detection experiment, and DM relic density, we find that the allowed parameter space of the scalar DM model will be completely excluded for the former cosmological observations, while it will increase for the latter ones. Those two cosmological observations lead to an almost paradoxical conclusion. Therefore, one could expect more stringent constraints on the WMIP DM models, with the accumulation of more accurate cosmological observations in the near future.

A Dark Matter WIMP That Can Be Detected and Definitively Identified with Currently Planned Experiments

A recently proposed dark matter WIMP (weakly interacting massive particle) has only second-order couplings to gauge bosons and itself. As a result, it has small annihilation, scattering, and creation cross-sections, and is consequently consistent with all current experiments and the observed abundance of dark matter. These cross-sections are, however, still sufficiently large to enable detection in experiments that are planned for the near future, and definitive identification in experiments proposed on a longer time scale. The (multi-channel) cross-section for annihilation is consistent with thermal production and freeze-out in the early universe, and with current evidence for dark matter annihilation in analyses of the observations of gamma rays by Fermi-LAT and antiprotons by AMS-02, as well as the constraints from Planck and Fermi-LAT. The cross-section for direct detection via collision with xenon nuclei is estimated to be slightly below 10−47 cm2, which should be attainable by LZ and Xenon nT and well within the reach of Darwin. The cross-section for collider detection via vector boson fusion is estimated to be ∼1 fb, and may be ultimately attainable by the high-luminosity LHC; definitive collider identification will probably require the more powerful facilities now being proposed.

Superheavy WIMP dark matter from incomplete thermalization

Although it is usually thought that a class of weakly interacting massive particle (WIMP) dark matters (DMs), which have the vector coupling with the Z boson, is denied by null results of the direct DM searches, such WIMP DMs are still viable if they are superheavy with the mass of mDM≳109 GeV. In the future, the superheavy WIMP DMs can be searched up to mDM≃1012 GeV, which corresponds to the so-called neutrino floor limit. We show that the observed abundance of ΩDMh2≃0.1 for a superheavy WIMP DM can be reproduced by a suitable reheating temperature of TR≃mDM/29 after inflation, if the direct inflaton decay into DM is negligible or kinematically forbidden.

Black holes and WIMPs: all or nothing or something else

ABSTRACT We consider constraints on primordial black holes (PBHs) in the mass range $(10^{-18}\!-\!10^{15})\, \mathrm{M}_{\odot }$ if the dark matter (DM) comprises weakly interacting massive particles (WIMPs) that form haloes around them and generate γ-rays by annihilations. We first study the formation of the haloes and find that their density profile prior to WIMP annihilations evolves to a characteristic power-law form. Because of the wide range of PBH masses considered, our analysis forges an interesting link between previous approaches to this problem. We then consider the effect of the WIMP annihilations on the halo profile and the associated generation of γ-rays. The observed extragalactic γ-ray background implies that the PBH DM fraction is $f^{}_{\rm PBH} \lesssim 2 \times 10^{-9}\, (m_{\chi } / {\rm TeV})^{1.1}$ in the mass range $2 \times 10^{-12}\, \mathrm{M}_{\odot }\, (m_{\chi } / {\rm TeV})^{-3.2} \lesssim M \lesssim 5 \times 10^{12}\, \mathrm{M}_{\odot }\, (m_{\chi } / {\rm TeV})^{1.1}$, where mχ and M are the WIMP and PBH masses, respectively. This limit is independent of M and therefore applies for any PBH mass function. For $M \lesssim 2\times 10^{-12}\, \mathrm{M}_{\odot }\, (m_{\chi }/ {\rm TeV})^{-3.2}$, the constraint on $f^{}_{\rm PBH}$ is a decreasing function of M and PBHs could still make a significant DM contribution at very low masses. We also consider constraints on WIMPs if the DM is mostly PBHs. If the merging black holes recently discovered by LIGO/Virgo are of primordial origin, this would rule out the standard WIMP DM scenario. More generally, the WIMP DM fraction cannot exceed 10−4 for $M \gt 10^{-9}\, \mathrm{M}_{\odot }$ and $m_{\chi } \gt 10\,$ GeV. There is a region of parameter space, with $M \lesssim 10^{-11}\, \mathrm{M}_{\odot }$ and $m_{\chi } \lesssim 100\,$ GeV, in which WIMPs and PBHs can both provide some but not all of the DM, so that one requires a third DM candidate.