11th Week Paper List
Search for Dark Matter WIMPs using Upward Through-going Muons in Super-Kamiokande
Super-Kamiokande Collaboration: S. Desai, Y. Ashie, S. Fukuda, Y. Fukuda, K. Ishihara, Y. Itow, Y. Koshio, A. Minamino, M. Miura, S. Moriyama, M. Nakahata, T. Namba, R. Nambu, Y. Obayashi, N. Sakurai, M. Shiozawa, Y. Suzuki, H. Takeuchi, Y. Takeuchi, S. Yamada, M. Ishitsuka, T. Kajita, K. Kaneyuki, S. Nakayama, A. Okada, T. Ooyabu, C. Saji, M. Earl, E. Kearns, J.L. Stone, L.R. Sulak, C.W. Walter, W. Wang, M. Goldhaber, T. Barszczak, D. Casper, J.P. Cravens, W. Gajewski, W.R. Kropp, S. Mine, D.W. Liu, M.B. Smy, H.W. Sobel, C.W. Sterner, M.R. Vagins, K.S. Ganezer, J. Hill, W.E. Keig, J.Y. Kim, I.T. Lim, R.W. Ellsworth, S. Tasaka, G. Guillian, A. Kibayashi, J.G. Learned, S. Matsuno, D. Takemori, M.D. Messier, Y. Hayato, A. K. Ichikawa, T. Ishida, T. Ishii, T. Iwashita, J. Kameda, T. Kobayashi, et al. (70 additional authors not shown)
We present the results of indirect searches for Weakly Interacting Massive Particles (WIMPs) with 1679.6 live days of data from the Super-Kamiokande detector using neutrino-induced upward through-going muons. The search is performed by looking for an excess of high energy muon neutrinos from WIMP annihilations in the Sun, the core of the Earth, and the Galactic Center, as compared to the number expected from the atmospheric neutrino background. No statistically significant excess was seen. We calculate flux limits in various angular cones around each of the above celestial objects. We obtain conservative model-independent upper limits on WIMP-nucleon cross-section as a function of WIMP mass and compare these results with the corresponding results from direct dark matter detection experiments.
Fermi-LAT Collaboration
The dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are some of the most dark matter (DM) dominated objects known. We report on gamma-ray observations of Milky Way dSphs based on 6 years of Fermi Large Area Telescope data processed with the new Pass 8 event-level analysis. None of the dSphs are significantly detected in gamma rays, and we present upper limits on the DM annihilation cross section from a combined analysis of 15 dSphs. These constraints are among the strongest and most robust to date and lie below the canonical thermal relic cross section for DM of mass ≲ 100 GeV annihilating via quark and τ-lepton channels.
Links : https://arxiv.org/abs/1503.02641
An estimate of the DM profile in the Galactic bulge region
Fabio Iocco, Maria Benito
We present an analysis of the mass distribution in the region of the Galactic bulge, which leads to constraints on the total amount and distribution of Dark Matter (DM) therein. Our results -based on the dynamical measurement of the BRAVA collaboration- are quantitatively compatible with those of a recent analysis, and generalised to a vaste sample of observationally inferred morphologies of the stellar components in the region of the Galactic bulge. By fitting the inferred DM mass to a generalised NFW profile, we find that cores (index gamma smaller than 0.6) are forbidden only for very light configurations of the bulge, and that cusps (index gamma bigger than 1.2) are allowed, but not necessarily preferred. Interestingly, we find that the results for the bulge region are compatible with those obtained with dynamical methods (based on the rotation curve) applied to outer regions of the Milky Way, for all morphologies adopted. We find that the uncertainty on the shape of the stellar morphology heavily affects the determination of the DM distribution in the bulge region, which is gravitationally dominated by baryons, adding up to the uncertainty on its normalization. The combination of the two hinders the actual possibility to infer sound conclusions about the distribution of DM in the region of the Galactic bulge, and only future observations of the stellar census and dynamics in this region will bring us closer to a quantitatively more definite answer.
Links : https://arxiv.org/abs/1611.09861
A tale of dark matter capture, sub-dominant WIMPs, and neutrino observatories
Sebastian Baum, Luca Visinelli, Katherine Freese, Patrick Stengel
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.
Links : https://arxiv.org/abs/1611.09665
Constraining the monochromatic gamma-rays from dark matter annihilation by the LHC
Arman Esmaili, Sara Khatibi, Mojtaba Mohammadi Najafabadi
The installation of forward detectors in CMS and ATLAS turn the LHC to an effective photon-photon collider. The elastic scattering of the beam-protons via the emission of photons, which can be identified by tagging the intact protons in the forward detectors, provides a powerful diagnostic of the central production of new particles through photon-photon annihilation. In this letter we study the central production of dark matter particles and the potential of LHC to constrain the cross section of this process. By virtue of the crossing symmetry, this limit can immediately be used to constrain the production of monochromatic gamma-rays in dark matter annihilation, a smoking gun signal under investigation in indirect dark matter searches. We show that with the integrated luminosity L=30 fb−1 in LHC at center-of-mass energy s√= 13 TeV, for dark matter masses ∼(50−600) GeV, a model-independent constraint on the cross section of dark matter annihilation to monochromatic gamma-rays at the same order of magnitude as the current Fermi-LAT and the future limits from CTA, can be obtained.
Links : https://arxiv.org/abs/1611.09320
Hadronically decaying heavy dark matter and high-energy neutrino limits
M.Yu. Kuznetsov
We consider dark matter consisting of long-living particles with masses 107 ≲ M ≲ 1016 GeV decaying through hadronic channel as a source of high energy neutrinos. Using recent data on high energy neutrino from IceCube and Pierre Auger experiments we derive the upper-limits on neutrino flux from dark matter decay and constraints on dark matter parameter space. The constraints derived are weaker that these obtained for the same dark matter models using the high energy gamma-ray limits.
Links : https://arxiv.org/abs/1611.08684
Substructure considerations rule out dark matter interpretation of Fermi Galactic Center excess
Hamish A. Clark, Pat Scott, Roberto Trotta, Geraint F. Lewis
An excess of gamma rays has been identified at the center of the Milky Way, and annihilation of dark matter has been posited as a potential source. This hypothesis faces significant challenges: difficulty characterizing astrophysical backgrounds, the need for a non-trivial adiabatic contraction of the inner part of the Milky Way's dark matter halo, and recent observations of photon clustering, which suggest that the majority of the excess is due to unresolved point sources. Here we point out that the point-like nature of the emission rules out the dark matter interpretation of the excess entirely. Attempting to model the emission with dark matter point sources either worsens the problem with the inner slope, requires an unrealistically large minihalo fraction toward the Galactic Center, or overproduces the observed emission at higher latitudes.
Links : https://arxiv.org/abs/1612.01539