Phenomenology of Dark Matter annihilation into a long-lived intermediate state

Journal of Cosmology and Astroparticle Physics (Impact Factor: 5.81). 03/2009; 07(7). DOI: 10.1088/1475-7516/2009/07/018
Source: arXiv


We propose a scenario where Dark Matter (DM) annihilates into an intermediate state which travels a distance $\lambda \equiv v/\Gamma$ on the order of galactic scales and then decays to Standard Model (SM) particles. The long lifetime disperses the production zone of the SM particles away from the galactic center and hence, relaxes constraints from gamma ray observations on canonical annihilation scenarios. We utilize this set up to explain the electron and positron excesses observed recently by PAMELA, ATIC, and FERMI. While an explanation in terms of usual DM annihilations seems to conflict with gamma ray observations, we show that within the proposed scenario, the PAMELA/ATIC/FERMI results are consistent with the gamma ray data. The distinction from decay scenarios is discsussed and we comment on the prospects for DM production at LHC. The typical decay length $\lambda \gtrsim 10$ kpc of the intermediate state can have its origin from a dimension six operator suppressed by a scale $\Lambda \sim 10^{13}$ GeV, which is roughly the seesaw scale for neutrino masses. Comment: 22 pages, 7 figures, added appendix B, published version

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Available from: Thomas Schwetz-Mangold, Jan 01, 2015
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    • "[21] [22]. It is possible, however, that DM does not annihilate directly into SM particles, but rather into metastable mediators which subsequently decay into SM states, χχ → V V → SM, as recently discussed in [23] [24] [25] [26] [27]. In such models, the thermal relic WIMP DM scenario can be realised as usual, while there is also the potential to explain astrophysical observations, e.g. the positron excess observed by PAMELA [25] [26]. "
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    ABSTRACT: We calculate the neutrino signal resulting from annihilation of secluded dark matter in the Sun. In this class of models, dark matter annihilates first into metastable mediators, which subsequently decay into Standard Model particles. If the mediators are long lived, they will propagate out from the dense solar core before decaying. High energy neutrinos undergo absorption in the Sun. In the standard scenario in which neutrinos are produced directly in the centre of the Sun, absorption is relevant for E > 100 GeV, resulting in a significant suppression of the neutrino spectrum beyond E ~ 1 TeV. In the secluded dark matter scenario, the neutrino signal is greatly enhanced because neutrinos are injected away from the core, at lower density. Since the solar density falls exponentially with radius, metastable mediators have a significant effect on the neutrino flux, even for decay lengths which are small compared to the solar radius. Moreover, since neutrino detection cross sections grow with energy, this enhancement of the high energy region of the neutrino spectrum would have a large effect on overall event rates.
    Full-text · Article · Feb 2011 · Journal of Cosmology and Astroparticle Physics
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    • "Therefore, the best discovery potential for V in this parameter range would probably be a high-intensity electron beam on a thin target [79]. Lastly, the lifetimes – 31 – of mediators in excess of milliseconds lead to interesting effects in the annihilation of dark matter, when the decays of mediators occur away from the point where the annihilation occur [80] [81] [82]. This leads to novel signatures in the indirect detection of dark matter in models with light mediators. "
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    ABSTRACT: The persistent discrepancy between observations of 7Li with putative primordial origin and its abundance prediction in Big Bang Nucleosynthesis (BBN) has become a challenge for the standard cosmological and astrophysical picture. We point out that the decay of GeV-scale metastable particles X may significantly reduce the BBN value down to a level at which it is reconciled with observations. The most efficient reduction occurs when the decay happens to charged pions and kaons, followed by their charge exchange reactions with protons. Similarly, if X decays to muons, secondary electron antineutrinos produce a similar effect. We consider the viability of these mechanisms in different classes of new GeV-scale sectors, and find that several minimal extensions of the Standard Model with metastable vector and/or scalar particles are capable of solving the cosmological lithium problem. Such light states can be a key to the explanation of recent cosmic ray anomalies and can be searched for in a variety of high-intensity medium-energy experiments. Comment: 50 pages, 13 figures; references added, typo corrected
    Preview · Article · Jun 2010 · Physical review D: Particles and fields
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    • "In order to realize the long-lived intermediate state proposal of ref. [20], it is interesting to know how small "
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    ABSTRACT: Numerous experimental anomalies hint at the existence of a dark matter (DM) multiplet χi with small mass splittings. We survey the simplest such models which arise from DM in the low representations of a new SU(2) gauge symmetry, whose gauge bosons have a small mass μ≲1 GeV. We identify preferred parameters Mχ≅1 TeV, μ∼100 MeV, αg∼0.04, and the χχ→4e annihilation channel, for explaining PAMELA, Fermi, and INTEGRAL/SPI lepton excesses, while remaining consistent with constraints from relic density, diffuse gamma rays, and the CMB. This consistency is strengthened if DM annihilations occur mainly in subhalos, while excitations (relevant to the excited DM proposal to explain the 511 keV excess) occur in the galactic center, due to higher velocity dispersions in the galactic center, induced by baryons. We derive new constraints and predictions which are generic to these models. Notably, decays of excited DM states χ′→χγ arise at one loop and could provide a new signal for INTEGRAL/SPI; big bang nucleosynthesis constraints on the density of dark SU(2) gauge bosons imply a lower bound on the mixing parameter ϵ between the SU(2) gauge bosons and photon. These considerations rule out the possibility of the gauge bosons that decay into e+e- being long-lived. We study in detail models of doublet, triplet, and quintuplet DM, showing that both normal and inverted mass hierarchies can occur, with mass splittings that can be parametrically smaller [e.g., O(100) keV] than the generic MeV scale of splittings. A systematic treatment of Z2 symmetry, which insures the stability of the intermediate DM state, is given for cases with inverted mass hierarchy, of interest for boosting the 511 keV signal from the excited dark matter mechanism.
    Preview · Article · Oct 2009 · Physical review D: Particles and fields
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