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Precise Relic WIMP Abundance and its Impact on Searches for Dark Matter Annihilation
Gary Steigman, Basudeb Dasgupta, John F. Beacom
If dark matter (DM) is a weakly interacting massive particle (WIMP) that is a thermal relic of the early Universe, then its total self-annihilation cross section is revealed by its present-day mass density. The canonical thermally averaged cross section for a generic WIMP is usually stated as 3*10^-26 cm^3s^-1, with unspecified uncertainty, and taken to be independent of WIMP mass. Recent searches for annihilation products of DM annihilation have just reached the sensitivity to exclude this canonical cross section for 100% branching ratio to certain final states and small WIMP masses. The ultimate goal is to probe all kinematically allowed final states as a function of mass and, if all states are adequately excluded, set a lower limit to the WIMP mass. Probing the low-mass region is further motivated due to recent hints for a light WIMP in direct and indirect searches. We revisit the thermal relic abundance calculation for a generic WIMP and show that the required cross section can be calculated precisely. It varies significantly with mass at masses below 10 GeV, reaching a maximum of 5.2*10^-26 cm^3s^-1 at masses around 0.3 GeV, and is 2.2*10^-26 cm^3s^-1 with feeble mass-dependence for masses above 10 GeV. These results, which differ significantly from the canonical value and have not been taken into account in searches for annihilation products from generic WIMPs, have a noticeable impact on the interpretation of present limits from Fermi-LAT and WMAP+ACT.
Links : https://arxiv.org/abs/1204.3622
Observation of an anomalous positron abundance in the cosmic radiation
O. Adriani, G. C. Barbarino, G. A. Bazilevskaya, R. Bellotti, M. Boezio, E. A. Bogomolov, L. Bonechi, M. Bongi, V. Bonvicini, S. Bottai, A. Bruno, F. Cafagna, D. Campana, P. Carlson, M. Casolino, G. Castellini, M. P. De Pascale, G. De Rosa, N. De Simone, V. Di Felice, A. M. Galper, L. Grishantseva, P. Hofverberg, S. V. Koldashov, S. Y. Krutkov, A. N. Kvashnin, A. Leonov, V. Malvezzi, L. Marcelli, W. Menn, V. V. Mikhailov, E. Mocchiutti, S. Orsi, G. Osteria, P. Papini, M. Pearce, P. Picozza, M. Ricci, S. B. Ricciarini, M. Simon, R. Sparvoli, P. Spillantini, Y. I. Stozhkov, A. Vacchi, E. Vannuccini, G. Vasilyev, S. A. Voronov, Y. T. Yurkin, G. Zampa, N. Zampa, V. G. Zverev
Positrons are known to be produced in interactions between cosmic-ray nuclei and interstellar matter ("secondary production"). Positrons may, however, also be created by dark matter particle annihilations in the galactic halo or in the magnetospheres of near-by pulsars. The nature of dark matter is one of the most prominent open questions in science today. An observation of positrons from pulsars would open a new observation window on these sources. Here we present results from the PAMELA satellite experiment on the positron abundance in the cosmic radiation for the energy range 1.5 - 100 GeV. Our high energy data deviate significantly from predictions of secondary production models, and may constitute the first indirect evidence of dark matter particle annihilations, or the first observation of positron production from near-by pulsars. We also present evidence that solar activity significantly affects the abundance of positrons at low energies.
Links : https://arxiv.org/abs/0810.4995
A search for Secluded Dark Matter in the Sun with the ANTARES neutrino telescope
S. Adrián-Martínez, A. Albert, M. André, G. Anton, M. Ardid, J.-J. Aubert, T. Avgitas, B. Baret, J. Barrios-Martí, S. Basa, V. Bertin, S. Biagi, R. Bormuth, M. Bou-Cabo, M.C. Bouwhuis, R. Bruijn, J. Brunner, J. Busto, A. Capone, L. Caramete, J. Carr, S. Celli, T. Chiarusi, M. Circella, A. Coleiro, R. Coniglione, H. Costantini, P. Coyle, A. Creusot, A. Deschamps, G. De Bonis, C. Distefano, C. Donzaud, D. Dornic, D. Drouhin, T. Eberl, I. El Bojaddaini, D. Elsässer, A. Enzenhöfer, K. Fehn, I. Felis, L.A. Fusco, S. Galatà, P. Gay, S. Geißelsöder, K. Geyer, V. Giordano, A. Gleixner, H. Glotin, R. Gracia-Ruiz, K. Graf, S. Hallmann, H. van Haren, A.J. Heijboer, Y. Hello, J.J. Hernández-Rey, J. Hößl, J. Hofestädt, C. Hugon, G. Illuminati, et al. (58 additional authors not shown)
A search for Secluded Dark Matter annihilation in the Sun using 2007-2012 data of the ANTARES neutrino telescope is presented. Three different cases are considered: a) detection of dimuons that result from the decay of the mediator, or neutrino detection from: b) mediator that decays into a dimuon and, in turn, into neutrinos, and c) mediator that decays directly into neutrinos. As no significant excess over background is observed, constraints are derived on the dark matter mass and the lifetime of the mediator.
Kimberly K. Boddy, Keith R. Dienes, Doojin Kim, Jason Kumar, Jong-Chul Park, Brooks Thomas
Many models currently exist which attempt to interpret the excess of gamma rays emanating from the Galactic Center in terms of annihilating or decaying dark matter. These models typically exhibit a variety of complicated cascade mechanisms for photon production, leading to a non-trivial kinematics which obscures the physics of the underlying dark sector. In this paper, by contrast, we observe that the spectrum of the gamma-ray excess may actually exhibit an intriguing "energy-duality" invariance under Eγ→E2∗/Eγ for some E∗. As we shall discuss, such an energy duality points back to a remarkably simple alternative kinematics which in turn is realized naturally within the Dynamical Dark Matter framework. Observation of this energy duality could therefore provide considerable information about the properties of the dark sector from which the Galactic-Center gamma-ray excess might arise, and highlights the importance of acquiring more complete data for the Galactic-Center excess in the energy range around 1 GeV.
Links : https://arxiv.org/abs/1609.09104
Toward (Finally!) Ruling Out Z and Higgs Mediated Dark Matter Models
Miguel Escudero, Asher Berlin, Dan Hooper, Meng-Xiang Lin
In recent years, direct detection, indirect detection, and collider experiments have placed increasingly stringent constraints on particle dark matter, exploring much of the parameter space associated with the WIMP paradigm. In this paper, we focus on the subset of WIMP models in which the dark matter annihilates in the early universe through couplings to either the Standard Model Z or the Standard Model Higgs boson. Considering fermionic, scalar, and vector dark matter candidates within a model-independent context, we find that the overwhelming majority of these dark matter candidates are already ruled out by existing experiments. In the case of Z mediated dark matter, the only scenario that is not already experimentally excluded is that of a fermionic dark matter candidate with an axial coupling and with a mass within a few GeV of the Z resonance (mDM≃mZ/2). Several Higgs mediated scenarios are currently viable if the mass of the dark matter is near the Higgs pole (mDM≃mH/2). Otherwise, the only scenarios that are not excluded are those in which the dark matter is a scalar (vector) heavier than 400 GeV (1160 GeV) with a Higgs portal coupling, or a fermion with a pseudoscalar (CP violating) coupling to the Standard Model Higgs boson. With the exception of dark matter with a purely pseudoscalar coupling to the Higgs, it is anticipated that planned direct detection experiments will probe the entire range of models considered in this study
Links : https://arxiv.org/abs/1609.09079
The core-halo mass relation of ultra-light axion dark matter from merger history
Xiaolong Du, Christoph Behrens, Jens C. Niemeyer, Bodo Schwabe
In the context of structure formation with ultra-light axion dark matter, we offer an alternative explanation for the mass relation of solitonic cores and their host halos observed in numerical simulations. Our argument is based entirely on the mass gain that occurs during major mergers of binary cores and largely independent of the initial core-halo mass relation assigned to hosts that have just collapsed. We find a relation between the halo mass Mh and corresponding core mass Mc, Mc∝M2β−1h, where (1−β) is the core mass loss fraction. Following the evolution of core masses in stochastic merger trees, we find empirical evidence for our model. Our results are useful for statistically modeling the effects of dark matter cores on the properties of galaxies and their substructures in axion dark matter cosmologies.
Links : https://arxiv.org/abs/1609.09414
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