Weakly Interacting Massive Particles Candidates Research Articles

Non-thermal WIMP production from higher order moduli decay

In a non-standard cosmological scenario heavy, long-lived particles, which we call moduli, dominate the energy density prior to Big Bang Nucleosynthesis. Weakly Interacting Massive Particles (WIMPs) may be produced non-thermally from moduli decays. The final relic abundance then depends on additional parameters such as the branching ratio of moduli to WIMPs and the modulus mass. This is of interest for WIMP candidates, such as a bino-like neutralino, where thermal production in standard cosmology leads to an overdensity. Previous works have shown that the correct dark matter (DM) relic density can then still be obtained if the moduli, with mass less than 107 GeV, decay to WIMPs with a branching ratio of less than 10-4. This upper bound could easily be violated once higher order corrections, involving final states with more than two particles, are included. We compute the branching ratios of three- and four-body decays of a modulus into final states involving two DM particles for general couplings. We then apply these expressions to sparticle production within the Minimal Supersymmetric Standard Model (MSSM) with neutralino DM. We find that this upper bound on the branching ratio can be satisfied in simplified models through an appropriate choice of as yet undetermined couplings. However, in the MSSM, it requires sparticle masses to be very close to half the modulus mass, in contrast to the idea of weak-scale supersymmetry.

Searching for TeV Dark Matter in Irregular Dwarf Galaxies with HAWC Observatory

We present the results of dark matter (DM) searches in a sample of 31 dwarf irregular (dIrr) galaxies within the field of view of the HAWC Observatory. dIrr galaxies are DM-dominated objects in which astrophysical gamma-ray emission is estimated to be negligible with respect to the secondary gamma-ray flux expected by annihilation or decay of weakly interacting massive particles (WIMPs). While we do not see any statistically significant DM signal in dIrr galaxies, we present the exclusion limits (95% C.L.) for annihilation cross section and decay lifetime for WIMP candidates with masses between 1 and 100 TeV. Exclusion limits from dIrr galaxies are relevant and complementary to benchmark dwarf Spheroidal (dSph) galaxies. In fact, dIrr galaxies are targets kinematically different from benchmark dSph, preserving the footprints of different evolution histories. We compare the limits from dIrr galaxies to those from ultrafaint and classical dSph galaxies previously observed with HAWC. We find that the constraints are comparable to the limits from classical dSph galaxies and ∼2 orders of magnitude weaker than the ultrafaint dSph limits.

Combined searches for dark matter in dwarf spheroidal galaxies observed with the MAGIC telescopes, including new data from Coma Berenices and Draco

Milky Way dwarf spheroidal galaxies (dSphs) are among the best candidates to search for signals of dark matter annihilation with Imaging Atmospheric Cherenkov Telescopes, given their high mass-to-light ratios and the fact that they are free of astrophysical gamma-ray emitting sources. Since 2011, MAGIC has performed a multi-year observation program in search for Weakly Interacting Massive Particles (WIMPs) in dSphs. Results on the observations of Segue 1 and Ursa Major II dSphs have already been published and include some of the most stringent upper limits (ULs) on the velocity-averaged cross-section 〈σannv〉 of WIMP annihilation from observations of dSphs. In this work, we report on the analyses of 52.1 h of data of Draco dSph and 49.5 h of Coma Berenices dSph observed with the MAGIC telescopes in 2018 and in 2019 respectively. No hint of a signal has been detected from either of these targets and new constraints on the 〈σannv〉 of WIMP candidates have been derived. In order to improve the sensitivity of the search and reduce the effect of the systematic uncertainties due to the J-factor estimates, we have combined the data of all dSphs observed with the MAGIC telescopes. Using 354.3 h of dSphs good quality data, 95% CL ULs on 〈σannv〉 have been obtained for 9 annihilation channels. For most of the channels, these results reach values of the order of 10−24cm3/s at ∼1 TeV and are the most stringent limits obtained with the MAGIC telescopes so far.

Probing low-mass WIMP candidates of dark matter with tetrafluoroethane superheated liquid detectors

Probing low mass (sub-GeV -- few GeV) Weakly Interacting Massive Particle (WIMP) candidates of dark matter through WIMP-induced nuclear recoils in direct detection experiments requires use of detector materials consisting of low mass target nuclei and low threshold energy. Here we explore the potential of superheated liquid detectors (SLD) with a hydrogen containing liquid, namely, tetrafluoroethane (C$_{2}$H$_{2}$F$_{4}$) (b.p.~$-26.3^\circ\,$C), as the target material for probing low mass WIMPs. It is found that few-keV level recoil energy thresholds possible for bubble nucleation by WIMP-induced $^{12}$C and $^{19}$F recoils in C$_{2}$H$_{2}$F$_{4}$ SLDs operated at atmospheric pressure and gamma-ray insensitive temperatures of $T\, \lesssim\, 35^\circ\,$C have the potential to allow WIMPs in the few-GeV mass range to be probed at a WIMP-nucleon spin-independent cross section sensitivity levels (90% C.L.) better than $4.6\times 10^{-5}\,$pb at WIMP masses down to $\sim$ 4 GeV with a total exposure of $\sim$ 1000 kg.day, provided that the ``thermodynamic efficiency" $\eta_{\rm T}$ that determines the bubble nucleation thresholds for the recoiling nuclei in C$_{2}$H$_{2}$F$_{4}$ is $\sim$ 50% or higher. Sensitivity to sub-GeV WIMP masses generally requires the detector to be sensitive to the WIMP-induced $^1$H recoils, which in turn requires the detector to be operated at temperatures $T\gtrsim 50^\circ\,$C and $\eta_{\rm T}$ close to 100%. At such relatively high temperatures (at atmospheric pressure), however, the detector would be sensitive to background gamma rays.

What is dark matter?

This study aims to review the early history of dark matter study, such as observational evidence from galactic rotational curves, gravitational lensing, and the cosmic microwave background, among others. The observation of the bullet clusters, which strongly supports the existence of dark matter rather than the theory of modified gravity, is discussed. The N body simulations also suggest the existence of cold non-relativistic dark matter and the existence of a universal form of the dark matter density distribution profile. We introduce a standard mechanism of thermal freeze-out for dark matter relic abundance, i.e., an explanation of how the dark matter particles that were kept in thermal equilibrium in the early stages of the universe are later unable to stay in equilibrium due to the expansion of the universe. The typical dark matter candidates are the so-called WIMPs (weakly interacting massive particles). Popular WIMP candidates include the lightest supersymmetric particles such as neutralinos. Other WIMP candidates such as the lightest T odd particles in the little Higgs models and the lightest KK (Kluza-Klein) modes in the universal extra dimension models are also discussed. Non-WIMP dark matter candidates such as axions are briefly discussed. The basic ideas and methods of dark matter detection, such as underground direct detection, which involves dark matter scattering off target nuclei, and indirect detection in space, which involves dark matter annihilation or decay in galaxies, are reviewed with a focus on recent experimental developments. For underground direct detection, we begin with the basic formulas for elastic dark matter nuclei scattering and the general features of nuclear number dependence. Three types of observables are discussed: (1) direct recoil events, (2) solar modulation of the recoil events, and (3) directional effects or the day-night differences of the events. Then, we focus on the experiments studying low-mass dark matter below 10 GeV, such as SuperCDMS (super cryogenic dark matter search) and CDEX (China dark matter experiment), among others, with a special focus on the CDEX experiment, which uses point contact germanium detectors. Experiments studying high-mass dark matter using liquid argon, such as Xenon, PandaX (particle and astrophysical xenon detector), and DarkSide are also discussed. Directional detection experiments, such as DRIFT (directional recoil identification from tracks) and MIMAC (MIcro-tpc MAtrix of Chambers), are briefly discussed. For indirect detection experiments in space, we first introduce the basic theory of dark matter signals in cosmic rays and then discuss the importance of the propagation effects of high-energy cosmic rays, such as electrons, positrons, protons, antiprotons, and heavier cosmic ray nuclei. The uncertainties originating from various sources are also discussed. We then review recent experimental results, such as that from Fermi LAT (Fermi large area telescope) and AMS-02(Alpha magnetic spectrometer 02), with a focus on the most recent dark matter particle explorer (DAMPE) experiments. As nearby sources may contribute to CRE (cosmic ray electron) structures at high energies, the recently released DAMPE results on the CRE flux, which hinted at a narrow excess at energy of 1.4 TeV, is discussed in some detail. In general, a spectral structure with a narrow width appears to reveal the space time distribution of the sources. Future perspectives of heavier cosmic-ray nuclei, such as anti-deuteron and anti-helium, are also reviewed.

Search for neutrinos from annihilation of captured low-mass dark matter particles in the sun by super-kamiokande.

Super-Kamiokande (SK) can search for weakly interacting massive particles (WIMPs) by detecting neutrinos produced from WIMP annihilations occurring inside the Sun. In this analysis, we include neutrino events with interaction vertices in the detector in addition to upward-going muons produced in the surrounding rock. Compared to the previous result, which used the upward-going muons only, the signal acceptances for light (few-GeV/c^{2}-200-GeV/c^{2}) WIMPs are significantly increased. We fit 3903 days of SK data to search for the contribution of neutrinos from WIMP annihilation in the Sun. We found no significant excess over expected atmospheric-neutrino background and the result is interpreted in terms of upper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about the annihilation channel. We set the current best limits on the spin-dependent WIMP-proton cross section for WIMP masses below 200 GeV/c^{2} (at 10 GeV/c^{2}, 1.49×10^{-39} cm^{2} for χχ→bb[over ¯] and 1.31×10^{-40} cm^{2} for χχ→τ^{+}τ^{-} annihilation channels), also ruling out some fraction of WIMP candidates with spin-independent coupling in the few-GeV/c^{2} mass range.

Constraints on light WIMP candidates from the isotropic diffuse gamma-ray emission

Motivated by the measurements reported by direct detection experiments, most notably DAMA, CDMS-II, CoGeNT and Xenon10/100, we study further the constraints that might be set on some light dark matter candidates, MDM ∼ few GeV, using the Fermi-LAT data on the isotropic gamma-ray diffuse emission. In particular, we consider a Dirac fermion singlet interacting through a new Z′ gauge boson, and a scalar singlet S interacting through the Higgs portal. Both candidates are WIMP (Weakly Interacting Massive Particles), i.e. they have an annihilation cross-section in the pbarn range. Also they may both have a spin-independent elastic cross section on nucleons in the range required by direct detection experiments. Although being generic WIMP candidates, because they have different interactions with Standard Model particles, their phenomenology regarding the isotropic diffuse gamma-ray emission is quite distinct. In the case of the scalar singlet, the one-to-one correspondence between its annihilation cross-section and its spin-independent elastic scattering cross-section permits to express the constraints from the Fermi-LAT data in the direct detection exclusion plot, σn0−MDM. Depending on the astrophysics, we argue that it is possible to exclude the singlet scalar dark matter candidate at 95% confidence level. The constraints on the Dirac singlet interacting through a Z′ are comparatively weaker.

DETECTION AND IDENTIFICATION OF DARK MATTER

Dark matter is an abundant component of our Universe and its detection and identification constitutes one of the most challenging goals in modern Physics. Particle Physics provides well motivated candidates for dark matter, among which a generic weakly-interacting massive particle (WIMP) stands out for its simplicity and the fact that WIMP candidates can be found in many theories proposing new physics at the TeV scale, such as Supersymmetry, models with Universal Extra Dimensions and Little Higgs Theories. I will review the properties of some of the main WIMP candidates and their detectability (with special emphasis on direct detection experiments). I will also address the strategies that can be used to discriminate among them in the case of a future detection.

Thermal decoupling of WIMPs from first principles

Weakly interacting massive particles (WIMPs) are arguably the most natural dark mattercandidates from a particle physics point of view. After their number density has frozen outin the early universe, thereby setting their relic density today, WIMPs are still kept veryclose to thermal equilibrium by scattering events with standard model particles. Thecomplete decoupling from the thermal bath happens as late as at temperatures of around∼1−10 MeV and provides an important cosmological scale that can directly be translated into asmall scale cut-off of the spectrum of matter density fluctuations. We present here a fullanalytic treatment of the kinetic decoupling process from first principles. This allows anexact determination of the decoupling scale, for arbitrary WIMP candidates and anyscattering amplitude. As an application, we consider the situation of the lightestsupersymmetric particle as well as the lightest Kaluza–Klein particle that arises in theorieswith universal extra dimensions; furthermore, we show that our formalism canalso easily be applied to, e.g., the evolution of the non-relativistic electrons intothe recombination regime. Finally, we comment on the impacts for the smallestgravitationally bound structures and the prospects for the indirect detection of darkmatter.

Bolometric WIMP search at Canfranc with different absorbers

The rare objects search with bolometers underground (ROSEBUD) is an experiment to search for weakly interacting massive particles (WIMPs) at the Canfranc Underground Laboratory with bolometric detectors. We present the progress achieved in the second phase of the experiment with three different absorbers (Al2O3, Ge and scintillating CaWO4). For the first time, different target nuclei have been used simultaneously in a common set-up, sharing identical external background conditions. Moreover, a discrimination of nuclear against electron recoils based on the simultaneous measurement of light and heat has been developed and applied to derive limits for WIMP candidates.

Results from the 1998–1999 runs of the cryogenic dark matter search

The Cryogenic Dark Matter Search (CDMS) uses low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interaction with atomic nuclei while discriminating against interactions of background particles. CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section are lower than those of any other experiment for WIMPs with masses between 10–70 GeV c −2. Under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit.

Cryogenic detection techniques at the canfranc underground laboratory: The ROSEBUD experiment

The rare objects search with bolometers underground (ROSEBUD) is an experiment to search for weakly interacting massive particles (WIMPs) at the Canfranc Underground Laboratory with bolometric detectors. We present the progress achieved in the second phase of the experiment with three different absorbers (Al2O3, Ge and scintillating CaWO4). For the first time, different target nuclei have been used simultaneously in a common set-up, sharing identical external background conditions. Moreover, a discrimination of nuclear against electron recoils based on the simultaneous measurement of light and heat has been developed and applied to derive limits for WIMP candidates.

Exclusion limits on the WIMP-nucleon cross section from the Cryogenic Dark Matter Search

The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.9% efficiency, and surface events are rejected with >95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons in all ways tested. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}. These limits border, but do not exclude, parameter space allowed by supersymmetry models and accelerator constraints. Results are compatible with some regions reported as allowed at 3-sigma by the annual-modulation measurement of the DAMA collaboration. However, under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the DAMA most likely value at >99.9% CL, and are incompatible with the model-independent annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit.

Supersymmetric dark matter

When combined with the wealth of observational evidence for a nonrelativistic matter density Ω 0≳0.3 , the big-bang-nucleosynthesis constraint on the baryon density, Ω b ≲0.1 indicates the existence of a significant amount of nonbaryonic dark matter. Several lines of reasoning suggest that the dark matter consists of some new, as yet undiscovered, weakly interacting massive particle (WIMP). Of the WIMP candidates that have been considered, perhaps the best-motivated and certainly the most theoretically developed is the neutralino, the lightest supersymmetric particle (LSP) in many supersymmetric theories. There is now a vast experimental effort being mounted to detect these particles in the Galactic halo. Techniques include direct detection in low-background laboratory detectors, indirect detection through observation of energetic neutrinos from annihilation of WIMPs that have accumulated in the Sun and/or the Earth, and observation of anomalous cosmic-ray antiprotons, positrons, and gamma rays.

Neutrino astronomy and search for WIMPs with MACRO

Upward-going muons, induced primarily by atmospheric neutrinos, are used to search for neutrinos of astrophysical origin. No evidence has been found looking at the event direction and flux limits are obtained on candidate sources. A space-time correlation between gamma ray bursts and upward-going muons has been also investigated. Furthermore the search for a neutrino signal from the Earth and the Sun induced by Weakly Interacting Massive Particles (WIMP) has been updated. The number of events from the Sun and from the Earth is compatible with the background from atmospheric neutrinos. Therefore flux limits for different search cones have been estimated. Here we concentrate on neutralinos as WIMP candidates and limits depending on the neutralino mass are given and compared with the prediction of supersymmetric models.