* Astronomy

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RE: Dark Matter Annihilation

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Title: Search for Dark Matter Annihilation Signals from the Fornax Galaxy Cluster with H.E.S.S
Authors: HESS Collaboration: A. Abramowski, F. Acero, F. Aharonian, A.G. Akhperjanian, G. Anton, A. Balzer, A. Barnacka, U. Barres de Almeida, Y. Becherini, J. Becker, B. Behera, K. Bernlöhr, E. Birsin, J. Biteau, A. Bochow, C. Boisson, J. Bolmont, P. Bordas, J. Brucker, F. Brun, P. Brun, T. Bulik, I. Büsching, S. Carrigan, S. Casanova, M. Cerruti, P.M. Chadwick, A. Charbonnier, R.C.G. Chaves, A. Cheesebrough, A.C. Clapson, G. Coignet, G. Cologna, J. Conrad, M. Dalton, M.K. Daniel, I.D. Davids, B. Degrange, C. Deil, H.J. Dickinson, A. Djannati-Ataï, W. Domainko, L.O'C. Drury, G. Dubus, K. Dutson, J. Dyks, M. Dyrda, K. Egberts, P. Eger, P. Espigat, L. Fallon, C. Farnier, S. Fegan, F. Feinstein, M.V. Fernandes, A. Fiasson, G. Fontaine, A. Förster, M. Fübling, Y.A. Gallant, et al. (137 additional authors not shown)

The Fornax galaxy cluster was observed with the High Energy Stereoscopic System (H.E.S.S.) for a total live time of 14.5 hours, searching for very-high-energy (VHE, E>100 GeV) gamma-rays from dark matter (DM) annihilation. No significant signal was found in searches for point-like and extended emissions. Using several models of the DM density distribution, upper limits on the DM velocity-weighted annihilation cross-section as a function of the DM particle mass are derived. Constraints are derived for different DM particle models, such as those arising from Kaluza-Klein and supersymmetric models. Various annihilation final states are considered. Possible enhancements of the DM annihilation gamma-ray flux, due to DM substructures of the DM host halo, or from the Sommerfeld effect, are studied. Additional gamma-ray contributions from internal bremsstrahlung and inverse Compton radiation are also discussed. For a DM particle mass of 1 TeV, the exclusion limits at 95% of confidence level reach values of ~ 10^-23cm^3s^-1, depending on the DM particle model and halo properties. Additional contribution from DM substructures can improve the upper limits on by more than two orders of magnitude. At masses around 4.5 TeV, the enhancement by substructures and the Sommerfeld resonance effect results in a velocity-weighted annihilation cross-section upper limit at the level of ~ 10^-26cm^3s^-1.

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Title: The impact of XENON100 and the LHC on Supersymmetric Dark Matter
Authors: Keith A. Olive

The effect of 2010 and 2011 LHC data are discussed in connection to the potential for the direct detection of supersymmetric dark matter. The impact of the recent XENON100 results are contrasted to these predictions.

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Title: Search for dark matter signals with Fermi-LAT observation of globular clusters NGC 6388 and M 15
Authors: Lei Feng (IHEP, NJU, J-CPNPC), Qiang Yuan (IHEP), Peng-Fei Yin (IHEP), Xiao-Jun Bi (IHEP), Mingzhe Li (NJU, J-CPNPC)

The globular clusters are probably good targets for dark matter (DM) searches in \gamma-rays due to the possible adiabatic contraction of DM by baryons. In this work we analyse the three-year data collected by Fermi Large Area Telescope of globular clusters NGC 6388 and M 15 to search for possible DM signals. For NGC 6388 the detection of \gamma-ray emission was reported by Fermi collaboration, which is consistent with the emission of a population of millisecond pulsars. The spectral shape of NGC 6388 is also shown to be consistent with a DM contribution if assuming the annihilation final state is b\bar{b}. No significant \gamma-ray emission from M 15 is observed. We give the upper limits of DM contribution to \gamma-ray emission in both NGC 6388 and M 15, for annihilation final states b\bar{b}, W^+W^-, \mu^+\mu^-, \tau^+\tau^- and monochromatic line. The constraints are stronger than that derived from observation of dwarf galaxies by Fermi.

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Title: Extragalactic and galactic gamma-rays and neutrinos from annihilating dark matter
Authors: Rouzbeh Allahverdi, Sheldon Campbell, Bhaskar Dutta

We describe cosmic gamma-ray and neutrino signals of dark matter annihilation, explaining how the complementarity of these signals provides additional information that, if observable, can enlighten the particle nature of dark matter. This is discussed in the context of exploiting the separate galactic and extragalactic components of the signal, using the spherical halo model distribution of dark matter. We motivate the discussion with supersymmetric extensions of the standard model of particle physics. We consider the minimal supersymmetric standard model (MSSM) where both neutrinos and gamma-rays are produced from annihilations. We also consider a gauged B-L, baryon number minus lepton number, extension of the MSSM, where annihilation can be purely to heavy right-handed neutrinos. We compare the galactic and extragalactic components of these signals, and conclude that it is not yet clear which may dominate when looking out of the galactic plane. To answer this question, we must have an understanding of the contribution of halo substructure to the annihilation signals. We find that different theories with indistinguishable gamma-ray signals can be distinguished in the neutrino signal. Gamma-ray annihilation signals are difficult to observe from the galactic center, due to abundant astrophysical sources; but annihilation neutrinos from there would not be so hidden, if they can be observed over the atmospheric neutrinos produced by cosmic rays.

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Title: Dark matter with photons
Authors: Álvaro de la Cruz-Dombriz, Viviana Gammaldi

If the present dark matter in the Universe annihilates into Standard Model particles, it must contribute to the gamma ray fluxes detected on the Earth. The magnitude of such contribution depends on the particular dark matter candidate, but certain features of the produced spectra may be analysed in a rather model-independent fashion. In this communication we briefly revise the complete photon spectra coming from WIMP annihilation into Standard Model particle-antiparticle pairs obtained by extensive Monte Carlo simulations and consequent fitting functions presented by Dombriz et al. in a wide range of WIMP masses. In order to illustrate the usefulness of these fitting functions, we mention how these results may be applied to the so-called brane-world theories whose fluctuations, the branons, behave as WIMPs and therefore may spontaneously annihilate in SM particles. The subsequent gamma-rays signal in the framework of dark matter indirect searches from Milky Way dSphs and Galactic Center may provide first evidences for this scenario.

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Title: Searching for Dark Matter Annihilation in M87
Authors: Sheetal Saxena, Dominik Elsässer, Michael Rüger, Alexander Summa, Karl Mannheim

Clusters of galaxies, such as the Virgo cluster, host enormous quantities of dark matter, making them prime targets for efforts in indirect dark matter detection via potential radiative signatures from annihilation of dark matter particles and subsequent radiative losses of annihilation products. However, a careful study of ubiquitous astrophysical backgrounds is mandatory to single out potential evidence for dark matter annihilation. Here, we construct a multiwavelength spectral energy distribution for the central radio galaxy in the Virgo cluster, M87, using a state-of-the-art numerical Synchrotron Self Compton approach. Fitting recent Chandra, Fermi-LAT and Cherenkov observations, we probe different dark matter annihilation scenarios including a full treatment of the inverse Compton losses from electrons and positrons produced in the annihilation. It is shown that such a template can substantially improve upon existing dark matter detection limits.

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Title: Measurement of separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope
Authors: The Fermi LAT Collaboration: M. Ackermann, M. Ajello, A. Allafort, L. Baldini, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, B. Berenji, R. D. Blandford, E. D. Bloom, E. Bonamente, A. W. Borgland, A. Bouvier, J. Bregeon, M. Brigida, P. Bruel, R. Buehler, S. Buson, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, J. M. Casandjian, C. Cecchi, E. Charles, A. Chekhtman, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, S. Cutini, A. de Angelis, F. de Palma, C. D. Dermer, S. W. Digel, E. do Couto e Silva, P. S. Drell, A. Drlica-Wagner, C. Favuzzi, S. J. Fegan, E. C. Ferrara, W. B. Focke, P. Fortin, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, D. Gasparrini, S. Germani, N. Giglietto, P. Giommi, F. Giordano, M. Giroletti, T. Glanzman, G. Godfrey, I. A. Grenier, J. E. Grove, et al. (90 additional authors not shown)

We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting the Earth's shadow, which is offset in opposite directions for opposite charges due to the Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 GeV and 200 GeV. We confirm that the fraction rises with energy in the 20--100 GeV range and determine for the first time that it continues to rise between 100 and 200 GeV.

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Title: Dense DM clumps seeded by cosmic string loops and DM annihilation
Authors: V.S. Berezinsky, V.I. Dokuchaev, Yu.N. Eroshenko

The annihilation of the dark matter in clumps around cosmic string loops is studied. These clumps form at the radiation dominated stage and may have densities \gg
ho_{eq}. We conclude that 100 GeV neutralino DM is incompatible with the range of the strings' tension 5 x 10^{-10}<G\mu/c^2<5.1 x 10^{-9} because the gamma-ray signal exceeds the Fermi-LAT limit in this case.

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Dark matter may solve 'radio filaments' mystery

Unexplained "filaments" of radio-wave emission close to our galaxy's centre may hold proof of the existence of dark matter, researchers have said.
Dark matter is believed to make up most of the mass of our Universe, but it has yet to be definitively spotted.
A report now suggests the filaments' emission arises from dark matter particles crashing into each other.
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