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Weakly interacting massive particles (WIMPs) can be gravitationally captured by the Sun and trapped in its core. The annihilation of those WIMPs into Standard Model particles produces a spectrum of neutrinos whose energy distribution is related to the dark matter mass. In this work, we present the theoretical framework for relating an observed neutrino flux to the WIMP-nucleon cross section and summarize a previous solar WIMP search carried out by IceCube. We then outline an ongoing updated solar WIMP search, focusing on improvements over the previous search.
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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/$c^2$ $sim$ 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 (SD) WIMP-proton cross section for WIMP masses below 200 GeV/$c^2$ (at 10 GeV/$c^2$, 1.49$times 10^{-39}$ cm$^2$ for $chichirightarrow b bar{b}$ and 1.31$times 10^{-40}$ cm$^2$ for $chichirightarrowtau^+tau^-$ annihilation channels), also ruling out some fraction of WIMP candidates with spin-independent (SI) coupling in the few-GeV/$c^2$ mass range.
The IceCube Neutrino Observatory has observed highly energetic neutrinos in excess of the expected atmospheric neutrino background. It is intriguing to consider the possibility that such events are probing physics beyond the standard model. In this context, $mathcal{O}$(PeV) dark matter particles decaying to neutrinos have been considered while dark matter annihilation has been dismissed invoking the unitarity bound as a limiting factor. However, the latter claim was done ignoring the contribution from dark matter substructure, which for PeV Cold Dark Matter would extend down to a free streaming mass of $mathcal{O}$($10^{-18}$M$_odot$). Since the unitarity bound is less stringent at low velocities, ($sigma_{rm ann}$v)$leq4pi/m_chi^2v$, then, it is possible that these cold and dense subhalos would contribute dominantly to a dark-matter-induced neutrino flux and easily account for the events observed by IceCube. A Sommerfeld-enhanced dark matter model can naturally support such scenario. Interestingly, the spatial distribution of the events shows features that would be expected in a dark matter interpretation. Although not conclusive, 9 of the 37 events appear to be clustered around a region near the Galactic Center while 6 others spatially coincide, within the reported angular errors, with 5 of 26 Milky Way satellites. However, a simple estimate of the probability of the latter occurring by chance is $sim35%$. More events are needed to statistically test this hypothesis. PeV dark matter particles are massive enough that their abundance as standard thermal relics would overclose the Universe. This issue can be solved in alternative scenarios, for instance if the decay of new massive unstable particles generates significant entropy reheating the Universe to a slightly lower temperature than the freeze-out temperature, $T_{rm RH} lesssim T_{rm f}sim4times10^4$~GeV.
We consider a new technique for neutrino energy and topology reconstruction at DUNE. In particular, we show that when the direction of the incoming neutrino is known, one can use the measured directions of the outgoing leptonic and hadronic particles to reconstruct poorly-measured quantities, such as the hadronic cascade energy. We show that this alternative technique yields an energy resolution which is comparable to current reconstruction methods which sum measured energies. As a proof of concept we apply this new reconstruction method to a search for dark matter annihilation in the Sun. We show that the use of directional information from both the leptonic and hadronic interaction products allows one to effectively reject backgrounds and isolate the signal, giving competitive sensitivities.
A search for a very-high-energy (VHE; >= 100 GeV) gamma-ray signal from self-annihilating particle Dark Matter (DM) is performed towards a region of projected distance r ~ 45-150 pc from the Galactic Center. The background-subtracted gamma-ray spectrum measured with the High Energy Stereoscopic System (H.E.S.S.) gamma-ray instrument in the energy range between 300 GeV and 30 TeV shows no hint of a residual gamma-ray flux. Assuming conventional Navarro-Frenk-White (NFW) and Einasto density profiles, limits are derived on the velocity-weighted annihilation cross section < sigma v> as a function of the DM particle mass. These are among the best reported so far for this energy range. In particular, for the DM particle mass of ~1 TeV, values for <sigma v> above 3 * 10^(-25) cm^3 s^(-1) are excluded for the Einasto density profile. The limits derived here differ much less for the chosen density profile parametrizations, as opposed to limits from gamma-ray observations of dwarf galaxies or the very center of the Milky Way, where the discrepancy is significantly larger.
A search for high-energy neutrinos coming from the direction of the Sun has been performed using the data recorded by the ANTARES neutrino telescope during 2007 and 2008. The neutrino selection criteria have been chosen to maximize the selection of possible signals produced by the self-annihilation of weakly interacting massive particles accumulated in the centre of the Sun with respect to the atmospheric background. After data unblinding, the number of neutrinos observed towards the Sun was found to be compatible with background expectations. The $90%$ CL upper limits in terms of spin-dependent and spin-independent WIMP-proton cross-sections are derived and compared to predictions of two supersymmetric models, CMSSM and MSSM-7. The ANTARES limits are competitive with those obtained by other neutrino observatories and are more stringent than those obtained by direct search experiments for the spin-dependent WIMP-proton cross-section.
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