Weakly Interacting Massive Particles Annihilation Research Articles

Antiproton bounds on dark matter annihilation from a combined analysis using the DRAGON2 code

Early studies of the AMS-02 antiproton ratio identified a possible excess over the expected astrophysical background that could be fit by the annihilation of a weakly interacting massive particle (WIMP). However, recent efforts have shown that uncertainties in cosmic-ray propagation, the antiproton production cross-section, and correlated systematic uncertainties in the AMS-02 data, may combine to decrease or eliminate the significance of this feature. We produce an advanced analysis using the DRAGON2 code which, for the first time, simultaneously fits the antiproton ratio along with multiple secondary cosmic-ray flux measurements to constrain astrophysical and nuclear uncertainties. Compared to previous work, our analysis benefits from a combination of: (1) recently released AMS-02 antiproton data, (2) updated nuclear fragmentation cross-section fits, (3) a rigorous Bayesian parameter space scan that constrains cosmic-ray propagation parameters.We find no statistically significant preference for a dark matter signal and set strong constraints on WIMP annihilation to bb̅, ruling out annihilation at the thermal cross-section for dark matter masses below ∼ 200 GeV. We do find a positive residual that is consistent with previous work, and can be explained by a ∼ 70 GeV WIMP annihilating below the thermal cross-section. However, our default analysis finds this excess to have a local significance of only 2.8σ, which is decreased to 1.8σ when the look-elsewhere effect is taken into account.

WIMPs in dilatonic Einstein Gauss-Bonnet cosmology

We use the Weakly Interacting Massive Particle (WIMP) thermal decoupling scenario to probe Cosmologies in dilatonic Einstein Gauss-Bonnet (dEGB) gravity, where the Gauss-Bonnet term is non-minimally coupled to a scalar field with vanishing potential.We put constraints on the model parameters when the ensuing modified cosmological scenario drives the WIMP annihilation cross section beyond the present bounds from DM indirect detection searches. In our analysis we assumed WIMPs that annihilate to Standard Model particles through an s-wave process. For the class of solutions that comply with WIMP indirect detection bounds, we find that dEGB typically plays a mitigating role on the scalar field dynamics at high temperature, slowing down the speed of its evolution and reducing the enhancement of the Hubble constant compared to its standard value. For such solutions, we observe that the corresponding boundary conditions at high temperature correspond asymptotically to a vanishing deceleration parameter q, so that the effect of dEGB is to add an accelerating term that exactly cancels the deceleration predicted by General Relativity.The bounds from WIMP indirect detection are nicely complementary to late-time constraints from compact binary mergers. This suggests that it could be interesting to use other Early Cosmology processes to probe the dEGB scenario.

A search for dark matter among Fermi-LAT unidentified sources with systematic features in machine learning

ABSTRACT Around one-third of the point-like sources in the Fermi-LAT catalogues remain as unidentified sources (unIDs) today. Indeed, these unIDs lack a clear, univocal association with a known astrophysical source. If dark matter (DM) is composed of weakly interacting massive particles (WIMPs), there is the exciting possibility that some of these unIDs may actually be DM sources, emitting gamma-rays from WIMPs annihilation. We propose a new approach to solve the standard, machine learning (ML) binary classification problem of disentangling prospective DM sources (simulated data) from astrophysical sources (observed data) among the unIDs of the 4FGL Fermi-LAT catalogue. We artificially build two systematic features for the DM data which are originally inherent to observed data: the detection significance and the uncertainty on the spectral curvature. We do it by sampling from the observed population of unIDs, assuming that the DM distributions would, if any, follow the latter. We consider different ML models: Logistic Regression, Neural Network (NN), Naive Bayes, and Gaussian Process, out of which the best, in terms of classification accuracy, is the NN, achieving around $93.3{{\ \rm per\ cent}} \pm 0.7{{\ \rm per\ cent}}$ performance. Other ML evaluation parameters, such as the True Negative and True Positive rates, are discussed in our work. Applying the NN to the unIDs sample, we find that the degeneracy between some astrophysical and DM sources can be partially solved within this methodology. None the less, we conclude that there are no DM source candidates among the pool of 4FGL Fermi-LAT unIDs.

Machine learning application for dark matter - background classification in JUNO experiment

Jiangmen underground neutrino observatory (JUNO) has a potential to indirectly detect dark matter (DM), observing neutrino events from annihilations of DM trapped by the gravitational force in the solar core. Weakly interacting massive particle (WIMP) DM candidate with mass > 4 GeV has significant solar capture rate. In this work, we simulate JUNO neutrino events from the most dominated WIMP annihilation channel, . Given the high-energy neutrinos from massive WIMPs, we extend the neutrino-nucleon interactions in the detector to include quasi-elastic (QE) and deep inelastic scatterings (DIS). The most challenging background events in the energy range above 100 MeV is the atmospheric neutrinos (atmo). The pulse shape discrimination (PSD) method is usually applied to distinguish between DM and atmo. In this work, we apply machine learning (ML) techniques to distinguish between the background (BG) atmo and DM neutrino events. We found that the random forest algorithm gives the best results. Using ML, the accuracy of DM-atmo events classification is 93.8% while similar f1-score could be achieved. On the other hand, only 78.1 % accuracy is obtained using conventional PSD with linear regression (LR). The upper limit for spin-dependent DM-proton cross-section with the applied ML is 5.84 × 10−40 cm2 for a 10 GeV WIMP DM which is an improvement over the sensitivity of the LR method of by a factor of ∼ 2.8x.

Revisiting constraints on WIMPs around primordial black holes

While primordial black holes (PBHs) with masses ${M}_{\mathrm{PBH}}\ensuremath{\gtrsim}{10}^{\ensuremath{-}11}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ cannot comprise the entirety of dark matter, the existence of even a small population of these objects can have profound astrophysical consequences. A subdominant population of PBHs will efficiently accrete dark matter particles before matter-radiation equality, giving rise to high-density dark matter spikes. We consider here the scenario in which dark matter is comprised primarily of weakly interacting massive particles (WIMPs) with a small subdominant contribution coming from PBHs, and revisit the constraints on the annihilation of WIMPs in these spikes using observations of the isotropic gamma-ray background (IGRB) and the cosmic microwave background (CMB), for a range of WIMP masses, annihilation channels, cross sections, and PBH mass functions. We find that the constraints derived using the IGRB have been significantly overestimated (in some cases by many orders of magnitude), and that limits obtained using observations of the CMB are typically stronger than, or comparable to, those coming from the IGRB. Importantly, we show that $\ensuremath{\sim}\mathcal{O}({M}_{\ensuremath{\bigodot}})$ PBHs can still contribute significantly to the dark matter density for sufficiently low WIMP masses and p-wave annihilation cross sections.

Constraints on primordial black holes with CMB spectral distortions

In the mixed dark matter scenarios consisting of primordial black holes (PBHs) and weakly interacting massive particles (WIMPs), WIMPs can be accreted onto PBHs to form ultracompact minihalos (UCMHs) with a density spike in the early universe. Compared with the classical dark matter halo, UCMHs are formed earlier and have a higher density of center. Since the annihilation rate is proportional to the squared number density of WIMPs, it is expected that WIMPs annihilation within UCMHs is enhanced and has influences on the early universe. Between the time of recombination and matter-radiation equality, the energy released from WIMPs annihilation within UCMHs is injected into the Universe resulting in cosmic microwave background $y$-type distortion. We investigate these effects and derive the upper limits on the abundance of PBHs taking advantage of the observational results of a far infrared absolute spectrophotometer (FIRAS). We find that for the WIMPs mass range $1\ensuremath{\le}{m}_{\ensuremath{\chi}}\ensuremath{\le}1000\text{ }\text{ }\mathrm{GeV}$, the upper limits on the abundance of PBHs are $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\ensuremath{\le}{\mathrm{\ensuremath{\Omega}}}_{\mathrm{PBH}}\ensuremath{\le}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$.

Radio bounds on the mixed dark matter scenarios of primordial black holes and WIMPs

We study the synchrotron radio emission in the mixed dark matter scenarios consisting of the primordial black holes (PBHs) and the self-annihilating WIMPs (weakly interacting massive particles). The WIMPs can form the ultracompact minihalos around PBHs and the annihilation enhancement from these dense halos can lead to the efficient synchrotron radiation at the radio frequency in the presence of galactic magnetic fields. The upper bound of PBH fraction with respect to the total dark matter abundance is of order 10-8 ∼ 10-5 depending on the electroweak scale WIMP mass (mχ = 10 ∼ 1000 GeV) and the WIMP annihilation channel (e.g. a hadronic χχ ⟶ bb̅ or a leptonic χχ ⟶ e + e - channel). The PBH contribution to the total dark matter abundance is hence negligible when the other component of dark matter is composed of the conventional electroweak scale WIMPs.

Primordial black hole dark matter in the presence of p-wave WIMP annihilation

We study the allowed primordial black hole (PBH) dark matter abundance in the mixed dark matter scenarios consisting of PBHs and self-annihilating weakly interacting massive particles (WIMPs) with a velocity dependent annihilation cross section. We first briefly illustrate how the WIMP dark matter halo profile changes for the velocity suppressed p-wave annihilation scenarios, compared with the familiar s-wave annihilation scenarios, and then discuss the PBH mass dependent upper bound on the allowed PBH dark matter abundance. The WIMPs can accrete onto a PBH to form an ultracompact minihalo with a spiky density profile. Such a spike is moderated in the central region of a halo because the WIMPs are annihilated away and this moderation is less effective for a smaller annihilation cross section. The WIMP core density becomes larger while the core radius becomes smaller for a velocity suppressed p-wave annihilation cross section than those for the s-wave annihilation scenarios. The annihilation cross section is dependent on the velocity which varies across the halo, and, in addition to the change of the WIMP density profile, another interesting feature is the PBH mass dependent bound on PBH dark matter abundance. This is in stark contrast to the s-wave annihilation scenarios where the PBH abundance bound is independent of the PBH mass. The allowed PBH dark matter fraction (with respect to the total dark matter abundance) is of order f PBH ≲ \U0001d4aa(10−7)(M⊙/MPBH)(−6+2γsp)/(3γsp+3) for the thermal relic p-wave dark matter with the mass 100 GeV where γsp is the slope index of the spike profile, to be compared with f PBH ≲ \U0001d4aa(10−9) for the corresponding thermal relic s-wave dark matter scenarios.

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.

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.

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.

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.

Constraining mixed dark-matter scenarios of WIMPs and primordial black holes from CMB and 21-cm observations

We consider the dark-matter (DM) scenarios consisting of the mixture of weakly interacting massive particles (WIMPs) and primordial black holes (PBHs) and study what fraction of the total DM can be PBHs. In such scenarios, PBHs can accrete the WIMPs and consequently enhance the heating and ionization in the intergalactic medium due to WIMP annihilations. We demonstrate that the CMB data can give stringent bounds on the allowed PBH fraction which are comparable to or even tighter than those from the gamma-ray data depending on the DM masses. For instance, the Markov-chain Monte Carlo likelihood analysis using the Planck CMB data leads to a bound on the PBH DM fraction with respect to the total dark matter ${f}_{\mathrm{PBH}}\ensuremath{\lesssim}\mathcal{O}({10}^{\ensuremath{-}10}\ensuremath{\sim}{10}^{\ensuremath{-}8})$ for the WIMP mass ${m}_{\ensuremath{\chi}}\ensuremath{\sim}\mathcal{O}(10\ensuremath{\sim}{10}^{3})\text{ }\text{ }\mathrm{GeV}$ with the conventional DM annihilation cross section $⟨\ensuremath{\sigma}v⟩=3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}26}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{3}/\mathrm{s}$. We also investigate the feasibility of the global 21-cm signal measurement to provide stringent constraints on the PBH fraction.

Stability and pulsation of the first dark stars

ABSTRACT The first bright objects to form in the Universe might not have been ‘ordinary’ fusion-powered stars, but ‘dark stars’ (DSs) powered by the annihilation of dark matter (DM) in the form of weakly interacting massive particles (WIMPs). If discovered, DSs can provide a unique laboratory to test DM models. DSs are born with a mass of the order of M⊙ and may grow to a few million solar masses; in this work we investigate the properties of early DSs with masses up to $\sim \! 1000 \, \mathrm{ M}_\odot$, fueled by WIMPS weighing 100 GeV. We improve the previous implementation of the DM energy source into the stellar evolution code mesa. We show that the growth of DSs is not limited by astrophysical effects: DSs up to $\sim \!1000 \, \mathrm{ M}_{\odot }$ exhibit no dynamical instabilities; DSs are not subject to mass-loss driven by super-Eddington winds. We test the assumption of previous work that the injected energy per WIMP annihilation is constant throughout the star; relaxing this assumption does not change the properties of the DSs. Furthermore, we study DS pulsations, for the first time investigating non-adiabatic pulsation modes, using the linear pulsation code gyre. We find that acoustic modes in DSs of masses smaller than $\sim \! 200 \, \mathrm{ M}_\odot$ are excited by the κ − γ and γ mechanism in layers where hydrogen or helium is (partially) ionized. Moreover, we show that the mass-loss rates potentially induced by pulsations are negligible compared to the accretion rates.

Searching for Sub-GeV dark matter in the galactic centre using Hyper-Kamiokande

Indirect detection of dark matter via its annihilation products is a key technique in the search for dark matter in the form of weakly interacting massive particles (WIMPs). Strong constraints exist on the annihilation of WIMPs to highly visible Standard Model final states such as photons or charged particles. In the case of s-wave annihilation, this typically eliminates thermal relic cross sections for dark matter of mass below \U0001d4aa(10) GeV . However, such limits typically neglect the possibility that dark matter may annihilate to assumed invisible or hard-to-detect final states, such as neutrinos. This is a difficult paradigm to probe due to the weak neutrino interaction cross section. Considering dark matter annihilation in the Galactic halo, we study the prospects for indirect detection using the Hyper-Kamiokande (HyperK) neutrino experiment, for dark matter of mass below 1 GeV . We undertake a dedicated simulation of the HyperK detector, which we benchmark against results from the similar Super-Kamiokande experiment and HyperK physics projections. We provide projections for the annihilation cross-sections that can be probed by HyperK for annihilation to muon or neutrino final states, and discuss uncertainties associated with the dark matter halo profile. For neutrino final states, we find that HyperK is sensitive to thermal annihilation cross-sections for dark matter with mass around 20 MeV, assuming an NFW halo profile. We also discuss the effects of neutron tagging, and prospects for improving the reach at low mass.

Radio constraints on dark matter annihilation in Canes Venatici I with LOFAR†

ABSTRACT Dwarf galaxies are dark matter (DM) dominated and therefore promising targets for the search for weakly interacting massive particles (WIMPs), which are well-known candidates for DM. The annihilation of WIMPs produces ultrarelativistic cosmic ray electrons and positrons that emit synchrotron radiation in the presence of magnetic fields. For typical magnetic field strengths (few μG) and $\mathcal {O}$(GeV–TeV) WIMP masses, this emission peaks at hundreds of MHz. Here, we use the non-detection of 150-MHz radio continuum emission from the dwarf spheroidal galaxy Canes Venatici I with the Low-Frequency Array to derive constraints on the annihilation cross-section of WIMPs into primary electron–positron and other fundamental particle–antiparticle pairs. Our main underlying assumption is that the transport of the cosmic rays can be described by the diffusion approximation, thus requiring a non-zero magnetic field strength with small-scale structure. In particular, by adopting magnetic field strengths of $\mathcal {O}(1\, \mu$G) and diffusion coefficients $\sim \!10^{27}~\rm cm^2\, s^{-1}$, we obtain limits that are comparable with those set by the Fermi Large Area Telescope using gamma-ray observations of this particular galaxy. Assuming s-wave annihilation and WIMPs making up 100 per cent of the DM density, our benchmark limits exclude several thermal WIMP realizations in the [2, 20]-GeV mass range. We caution, however, that our limits for the cross-section are subject to enormous uncertainties that we also quantitatively assess. In particular, variations on the propagation parameters or on the DM halo can shift our limits up by several orders of magnitude (in the pessimistic scenario).

(Non-)Thermal Production of WIMPs during Kination

Understanding the nature of the Dark Matter (DM) is one of the current challenges in modern astrophysics and cosmology. Knowing the properties of the DM particle would shed light on physics beyond the Standard Model and even provide us with details of the early Universe. In fact, the detection of such a relic would bring us information from the pre-Big Bang Nucleosynthesis (BBN) period, an epoch from which we have no direct data, and could even hint at inflation physics. In this work, we assume that the expansion rate of the Universe after inflation is governed by the kinetic energy of a scalar field ϕ , in the so-called “kination” model. Adding to previous work on the subject, we assume that the ϕ field decays into both radiation and DM particles, which we take to be Weakly Interacting Massive Particles (WIMPs). The present abundance of WIMPs is then fixed during the kination period through either a thermal “freeze-out” or “freeze-in” mechanism, or through a non-thermal process governed by the decay of ϕ . We explore the parameter space of this theory with the requirement that the present WIMP abundance provides the correct relic budget. Requiring that BBN occurs during the standard cosmological scenario sets a limit on the temperature at which the kination period ends. Using this limit and assuming the WIMP has a mass m χ = 100 GeV, we obtain that the thermally averaged WIMP annihilation cross section has to satisfy the constraints 4 × 10 − 16 GeV − 2 ≲ ⟨ σ v ⟩ ≲ 2 × 10 − 5 GeV − 2 in order for having at least one of the production mechanism to yield the observed amount of DM. This result shows how the properties of the WIMP particle, if ever measured, can yield information on the pre-BBN content of the Universe.

Constraints on dark matter models from the observation of Triangulum-II with the Fermi Large Area Telescope

Triangulum-II, a newly discovered dwarf spheroidal galaxy, is a strong candidate for the indirect search of dark matter through the detection of γ-ray emission that could originate from the pair- annihilation of weakly interacting massive particles (WIMPs). We here report on the analysis of almost seven years Fermi Gamma-Ray Space Telescope data of Triangulum-II which was taken during its all sky survey operation mode. No excess γ-ray emission has been detected above 100 MeV from Triangulum-II. We derive the upper limits on γ-ray flux assuming both the power-law spectra and the spectra related to WIMP annihilation. In this work, we have considered several theoretical WIMP (neutralinos here) models envisioning both thermal and non-thermal production of WIMPs, and put limits on pair-annihilation cross section of WIMPs to constrain the parameter space related to those theoretical models.

Dark matter capture, subdominant WIMPs, and neutrino observatories

Weakly Interacting Massive Particles (WIMPs), which are among the best motivated dark matter (DM) candidates, could make up all or only a fraction of the total DM budget. We consider a scenario in which WIMPs are a sub-dominant DM component; such a scenario would affect both current direct and indirect bounds on the WIMP-nucleon scattering cross section. In this paper we focus on indirect searches for the neutrino flux produced by annihilation of sub-dominant WIMPs captured by the Sun or the Earth via either spin-dependent or spin-independent scattering. We derive the annihilation rate and the expected neutrino flux at neutrino observatories. In our computation, we include an updated chemical composition of the Earth with respect to the previous literature, leading to an increase of the Earth's capture rate for spin-dependent scattering by a factor three. Results are compared with current bounds from Super-Kamiokande and IceCube. We discuss the scaling of bounds from both direct and indirect detection methods with the WIMP abundance.

Study of WIMP annihilations into a pair of on-shell scalar mediators

In this article, we focus on new scalar $\ensuremath{\phi}$ mediated scalar/vectorial weakly interacting massive particles (WIMPs) with $\ensuremath{\phi}$'s mass slightly below the WIMP mass. To explain the Galactic center 1--3 GeV gamma-ray excess, here we consider the case that a WIMP pair predominantly annihilates into an on-shell $\ensuremath{\phi}\ensuremath{\phi}$ pair with $\ensuremath{\phi}$ mainly decaying to $\ensuremath{\tau}\overline{\ensuremath{\tau}}$. The masses of WIMPs are in a range about 14--22 GeV, and the annihilations of WIMPs are phase space suppressed today. In this annihilation scheme, the couplings of the $\ensuremath{\phi}$-standard model (SM) particles are almost arbitrarily small, and the WIMP-nucleus spin-independent scattering can be tolerant by the present dark matter (DM) direct detections. A scalar mediator-Higgs field mixing is introduced, which is small and available. The lower limit on the couplings of the $\ensuremath{\phi}$-SM particles set by the thermal equilibrium in the early Universe is derived, and this constraint is above the neutrino background for scalar DM in direct detections. The WIMPs may be detectable at the upgraded DM direct detection experiment in the next few years, and the exotic decay $h\ensuremath{\rightarrow}\ensuremath{\phi}\ensuremath{\phi}$, the production of $\ensuremath{\phi}$ may be observable at the future high-luminosity ${e}^{+}{e}^{\ensuremath{-}}$ collider.