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Register a new userInterpretation of AMS-02 Results: Correlations among Dark Matter Signals
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The AMS-02 collaboration has recently released data on the positron fraction $e^+/(e^-+e^+)$ up to energies of about 350 GeV. If one insists on interpreting the observed excess as a dark matter signal, then we find it is best described by a TeV-scale dark matter annihilating into $tau^+tau^-$, although this situation is already severely constrained by gamma-ray measurements. The annihilation into $mu^+mu^-$ is allowed by gamma-rays more than $tau^+tau^-$, but it gives a poorer fit to textsc{AMS-02} data. Moreover, since electroweak corrections induce correlations among the fluxes of stable particles from dark matter annihilations, the recent AMS-02 data imply a well-defined prediction for the correlated flux of antiprotons. Under the assumption that their future measurements will not show any antiproton excess above the background, the dark matter interpretation of the positron rise will possibly be ruled out by only making use of data from a single experiment. This work is the first of a program where we emphasize the role of correlations among dark matter signals.
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We study a simple extension of the Standard Model supplemented by an electroweak triplet scalar field to accommodate small neutrino masses by the type-II seesaw mechanism, while an additional singlet scalar field can play the role of cold dark matter (DM) in our Universe. This DM candidate is leptophilic for a wide range of model parameter space, and the lepton flux due to its annihilation carries information about the neutrino mass hierarchy. Using the recently released high precision data on positron fraction and flux from the AMS-02 experiment, we examine the DM interpretation of the observed positron excess in our model for two kinematically distinct scenarios with the DM and triplet scalar masses (a) non-degenerate ($m_{rm DM}gg m_{Delta}$), and (b) quasi-degenerate ($m_{rm DM} simeq m_Delta$). We find that a good fit to the AMS-02 data can be obtained in both cases (a) and (b) with a normal hierarchy of neutrino masses, while the inverted hierarchy case is somewhat disfavored. Although we require a larger boost factor for the normal hierarchy case, this is still consistent with the current upper limits derived from Fermi-LAT and IceCube data for case (a). Moreover, the absence of an excess anti-proton flux as suggested by PAMELA data sets an indirect upper limit on the DM-nucleon spin-independent elastic scattering cross section which is stronger than the existing DM direct detection bound from LUX in the AMS-02 preferred DM mass range.
For explaining the AMS-02 cosmic positron excess, which was recently reported, we consider a scenario of thermally produced and decaying dark matter (DM) into the standard model (SM) leptons with an extremely small decay rate, Gamma_{DM} sim 10^{-26} sec.^{-1}. Since the needed DM mass is relatively heavy (700 GeV < m_{DM} < 3000 GeV), we introduce another DM component apart from the lightest supersymmetric particle (LSP). For its (meta-) stability and annihilation into other particles, the new DM should be accompanied with another Z_2 symmetry apart from the R-parity. Sizable renormalizable couplings of the new DM with SM particles, which are necessary for its thermalization in the early universe, cannot destabilize the new DM because of the new Z_2 symmetry. Since the new DM was thermally produced, it can naturally explain the present energy density of the universe. The new DM can decay into the SM leptons (and the LSP) only through non-renormalizable operators suppressed by a superheavy squared mass parameter after the new symmetry is broken around TeV scale. We realize this scenario in a model of gauged vector-like leptons, which was proposed recently for the naturalness of the Higgs boson.
We consider indirect detection of meta-stable dark matter particles decaying into a stable neutral particle and a pair of standard model fermions. Due to the softer energy spectra from the three-body decay, such models could potentially explain the AMS-02 positron excess without being constrained by the Fermi-LAT gamma-ray data and the cosmic ray anti-proton measurements. We scrutinize over different final state fermions, paying special attention to handling of the cosmic ray background and including various contributions from cosmic ray propagation with the help of the textsc{LikeDM} package. It is found that primary decays into an electron-positron pair and a stable neutral particle could give rise to the AMS-02 positron excess and, at the same time, stay unscathed against the gamma-ray and anti-proton constraints. Decays to a muon pair or a mixed flavor electron-muon pair may also be viable depending on the propagation models. Decays to all other standard model fermions are severely disfavored.
The Alpha Magnetic Spectrometer (AMS), to be installed on the International Space Station, will provide data on cosmic radiations in the energy range from 0.5 GeV to 3 TeV. The main physics goals are the anti-matter and the dark matter searches. Observations and cosmology indicate that the Universe may include a large amount of unknown Dark Matter. It should be composed of non baryonic Weakly Interacting Massive Particles (WIMP). In R-parity conserving models a good WIMP candidate is the lightest SUSY particle. AMS offers a unique opportunity to study simultaneously SUSY dark matter in three decay channels resulting from the neutralino annihilation: e+, antiproton and gamma. Either in the SUSY frame and in alternative scenarios (like extra-dimensions) the expected flux sensitivities as a function of energy in 3 year exposure for the e+/e- ratio, gamma and antiproton yields are presented.
Recently the AMS-02 experiment has released the data of positron fraction with much small statistical error. Because of the small error, it is no longer easy to fit the data with a single dark matter for a fixed diffusion model and dark matter profile. In this paper, we propose a new interpretation of the data that it originates from decay of two dark matter. This interpretation gives a rough threshold of the lighter DM component. When DM decays into leptons, the positron fraction in the cosmic ray depends on the flavor of the final states, and this is fixed by imposing non-Abelian discrete symmetry in our model. By assuming two gauge-singlet fermionic decaying DM particles, we show that a model with non-Abelian discrete flavor symmetry, e.g. $T_{13}$, can give a much better fitting to the AMS-02 data compared with single dark matter scenario. Few dimension six operators of universal leptonic decay of DM particles are allowed in our model since its decay operators are constrained by the $T_{13}$ symmetry. We also show that the lepton masses and mixings are consistent with current experimental data, due to the flavor symmetry.
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