Recent Studies

Dark matter searches for monoenergetic neutrinos arising from stopped meson decay in the Sun

Details: Journal of Cosmology and Astroparticle Physics(JCAP) (2015) / arXiv

Dark matter can be gravitationally captured by the Sun after scattering off solar nuclei. Annihilations of the dark matter trapped and accumulated in the centre of the Sun could result in one of the most detectable and recognizable signals for dark matter. Searches for high-energy neutrinos produced in the decay of annihilation products have yielded extremely competitive constraints on the spin-dependent scattering cross sections of dark matter with nuclei. Recently, the low energy neutrino signal arising from dark-matter annihilation to quarks which then hadronize and shower has been suggested as a competitive and complementary search strategy. These high-multiplicity hadronic showers give rise to a large amount of pions which will come to rest in the Sun and decay, leading to a unique sub-GeV neutrino signal. We here improve on previous works by considering the monoenergetic neutrino signal arising from both pion and kaon decay. We consider searches at liquid scintillation, liquid argon, and water Cherenkov detectors and find very competitive sensitivities for few-GeV dark matter masses.


First Observation of Time Variation in the Solar-Disk Gamma-Ray Flux with Fermi

Details: Physical Review D(PRD) (2016) / arXiv

Abstract: The solar disk is a bright gamma-ray source. Surprisingly, its flux is about one order of magnitude higher than predicted. As a first step toward understanding the physical origin of this discrepancy, we perform a new analysis in 1-100 GeV using 6 years of public Fermi-LAT data. Compared to the previous analysis by the Fermi Collaboration, who analyzed 1.5 years of data and detected the solar disk in 0.1-10 GeV, we find two new and significant results: (1). In the 1-10 GeV flux (detected at >5σ  ), we discover a significant time variation that anticorrelates with solar activity. (2). We detect gamma rays in 10-30 GeV at >5σ  , and in 30-100 GeV at >2σ  . The time variation strongly indicates that solar-disk gamma rays are induced by cosmic rays and that solar atmospheric magnetic fields play an important role. Our results provide essential clues for understanding the underlying gamma-ray production processes, which may allow new probes of solar atmospheric magnetic fields, cosmic rays in the solar system, and possible new physics. Finally, we show that the Sun is a promising new target for ground-based TeV gamma-ray telescopes such as HAWC and LHAASO.



Spectrometry of the Earth using Neutrino Oscillations

Details: Scientific Reports 5 (2015) / arXiv
The unknown constituents of the interior of our home planet have provoked the human imagination and driven scientific exploration. We herein demonstrate that large neutrino detectors could be used in the near future to significantly improve our understanding of the Earth’s inner chemical composition. Neutrinos, which are naturally produced in the atmosphere, traverse the Earth and undergo oscillations that depend on the Earth’s electron density. The Earth’s chemical composition can be determined by combining observations from large neutrino detectors with seismic measurements of the Earth’s matter density. We present a method that will allow us to perform a measurement that can distinguish between composition models of the outer core. We show that the next-generation large-volume neutrino detectors can provide sufficient sensitivity to reject extreme cases of outer core composition. In the future, dedicated instruments could be capable of distinguishing between specific Earth composition models and thereby reshape our understanding of the inner Earth in previously unimagined ways.




Super heavy dark matter and IceCube neutrino signals:bounds on decaying dark matter

Details: Physical Review D(PRD) (2015) / arXiv

Super heavy dark matter may show its presence in high energy neutrino signals detected on earth. From the latest results of Ice Cube, we could set the strongest lower bound on the lifetime of dark matter beyond 100 TeV around 1028 sec . The excess around a PeV is noticed and may be interpreted as the first signal of DM even though further confirmation and dedicated searches are invited.






The Leptoquark Implication from the CMS and IceCube Experiments

Details: Physical Review D(PRD) (2015) / arXiv

The recent excess in the CMS measurements of eejj  and eνjj  channels and the emergence of PeV comsic neutrino events at the IceCube experiment share an intriguing implication for a leptoquark with a 600-650 GeV mass. We investigate the CMS constraints on the flavor structure of a scenario with the minimal leptoquark Yukawa couplings and correlate such a scenario to the resonant enhancement in the very high energy shower event rates at the IceCube. We find for a single leptoquark, the CMS signals require large couplings to the third generation leptons. This leads to an enhancement in the ντ -nucleon scattering cross-section and subsequently more ντ events at PeV energies. However, a visible enhancement above the Standard Model scattering would require a leptoquark Yukawa coupling larger than one that can be easily tested at the upcoming LHC runs.






IceCube Dark Matter Searches and Future Perspectives

Details: AAPPS Bulletin Article (2015)

Dark matter could be detected through the observation of neutrinos originating from dark matter annihilations or decays. The world’s largest neutrino telescope, IceCube, is at the forefront of such indirect searches for evidence of beyond the standard model physics. Analyses of IceCube data have resulted in some of the most stringent constraints on dark matter annihilations, interactions with nucleons, and have spurred imaginations on the yet to be determined origin of the recently discovered high-energy astrophysical neutrino flux. In the future, improved analyses methods combined with high statistics samples of multiple years of IceCube data and later from detector expansions will provide significant potential for discovery of dark matter.



Solar WIMPs Unraveled: Experiments, astrophysical uncertainties, and interactive Tools

Details: Physics of Dark Universe (2014) / arXiv

The absence of a neutrino flux from self-annihilating dark matter captured in the Sun has tightly constrained some leading particle dark matter scenarios. The impact of astrophysical uncertainties on the capture process of dark matter in the Sun and hence also the derived constraints by neutrino telescopes need to be taken into account. In this review we have explored relevant uncertainties in solar WIMP searches, summarized results from leading experiments, and provided an outlook into upcoming searches and future experiments. We have created an interactive plotting tool that allows the user to view current limits and projected sensitivities of major experiments under changing astrophysical conditions.



Impact of the dark matter velocity distribution on capture rates in the Sun

Details: Journal of Cosmology and Astroparticle Physics(JCAP) (2014) / arXiv

Dark matter could be captured in the Sun and self-annihilate, giving rise to an observable neutrino flux. Indirect searches for dark matter looking for this signal with neutrino telescopes have resulted in tight constraints on the interaction cross-section of dark matter with ordinary matter. We investigate how robust limits are against astro-physical uncertainties. We study the effect of the velocity distribution of dark matter in our Galaxy on capture rates in the Sun. We investigate four sources of uncertainties: orbital speed of the Sun, escape velocity of dark matter from the halo, dark matter velocity distribution functions and existence of a dark disc. We find that even extreme cases currently discussed do not decrease the sensitivity of indirect detection significantly because the capture is achieved over a broad range of the velocity distribution by integration over the velocity distribution. The effect of the uncertainty in the high-velocity tail of dark matter halo is very marginal as the capture process is rather inefficient at this region. The difference in capture rate in the Sun for various scenarios is compared to the expected change in event rates for direct detection. The possibility of co-rotating structure with the Sun can largely boost the signal and hence makes the interpretation of indirect detection conservative compared to direct detection.