Highlights on gamma rays, neutrinos and antiprotons from TeV Dark Matter

It has been shown that the gamma-ray flux observed by HESS from the J1745-290 Galactic Center source is well fitted as the secondary gamma-rays photons generated from Dark Matter annihilating into Standard Model particles in combination with a simple power law background. The neutrino flux expected from such Dark Matter source has been also analyzed. The main results of such analyses for 50 TeV Dark Matter annihilating into W+W- gauge boson and preliminary results for antiprotons are presented.


Introduction
Multimessenger astroparticle study is fundamental for Dark Matter (DM) indirect search. Signatures of DM annihilating or decay in astrophysical sources may be observed in cosmic-ray fluxes by Cerenkov telescopes such as VERITAS, HESS, MAGIC and CTA; neutrino telescopes such as ANTARES or IceCube; satellites such as PAMELA, AMS and Fermi or ballon experiments like CAPRICE or BESS [1]. The secondary products of annihilation and decay of DM particles contribute to the cosmic-rays differential flux at the Earth as where: • η cr depends on the secondary particles of interest (observed cosmic-ray flux) and its propagation.
• the total flux is given by decay (a = 1) or annihilation (a = 2) events of DM particles into the i-th Standard Model (SM) particle (annihilation/decay channel). The ζ factor discerns between these two cases: ζ (1) i = 1/τ decay i and ζ (2) i = σ i v are respectively the inverse of the decay time and and thermal averaged annihilation cross section times velocity. The probability that DM annihilates or decays into the i-th channel depends on the nature of DM.
• the differential number dN (cr) i /dE of cosmic-rays produced at the source by subsequent events of annihilation or decay of SM particles is simulated by means of Monte Carlo events generator software, such as PYTHIA or HERWIG. Some uncertainties may be introduced in the evaluation of both the ζ (a) i and κ cr factor due to the choice of the Fortran or C++ versions of PYTHIA or HERWIG software, as discussed in [2]  • the κ cr factor depends on the astrophysics of DM distribution as well as on the cosmic-rays propagation. For neutral cosmic-rays (n-cr) it is the astrophysical factor Here, ρ(r) is the DM density in the halo and l is the distance from the Sun to any point in the Galaxy disk and halo. The radial distance r of any point in the halo is measured from the GC, and is related to l by r 2 = l 2 + D 2 − 2D l cos Ψ, where D 8.5 kpc is the distance from the Sun to the center of the Galaxy. The distance from the Sun to the edge of the halo in the direction θ from the GC is l max = D cos θ + r 2 − D 2 sin θ. For neutral particles, directional observations are achievable. In this case, the flux must be averaged over the solid angle of the detector, that is typically of order of ∆Ω = 2π(1 − cos Ψ), being Ψ the angular resolution of the telescope. For charged cosmic-rays (c-cr), directional observations are not feasible. In fact, charged particles observed in a given direction might have been originated everywhere in the sky. In this case the κ c-cr factor is proportional to a diffusion term The diffusion factor at the position of the sun R c-cr (r , E) for charged cosmic-ray (e ± , p ± etc.. ) is the solution of a diffusion equation that depends on the particle of interest and DM distribution. It describes the diffusion of particles in the Galaxy and the production of secondary cosmic-rays due to the interaction with the Interstellar Medium (ISM). The final flux at the position of the Earth also includes Solar magnetic field effect [3,4].
In Section 2, I present the main results of the cosmic-rays analysis of the prospective DM source at the GC: the gamma-rays cut-off detected by HESS at the Galactic Center and the prospective neutrino flux are reviewed. New constraints obtained from the antiprotons study are also presented in Section 2, while the conclusions are in Section 3.

Cosmic rays from TeV Dark Matter at the Galactic Center
In previous works it has been shown that the collection of data from HESS telescope from the J1749-290 source at the Galactic Center (GC) is well fitted by model independent DM annihilating into SM channels [5]. Such study provides gamma-rays fits with DM masses between 1 − 100 TeV. While annihilation in lepton channel is excluded at the 99% confidence level, gamma-rays secondary flux produced by DM annihilating into quark and bosons channels well reproduce the data. Here, Eq.(1) for the cosmic-rays differential flux at the Earth is discussed for heavy DM particle of ≈ 50 TeV annihilating into W + W − channel. Extra-dimensional particles as branons may justify TeV DM annihilating in boson channels [6,7].
Gamma-rays. The differential secondary gamma-ray flux emitted by DM annihilating 100% in W + W − SM channel can be easily written as the Eq. (1) with η γ = 1, and κ γ = J ∆Ω . Such gammaray flux from DM combined with a power-law background is able to fit HESS data from the GC and Fermi-LAT data [5]: with J NFW (2) 280 · 10 23 GeV 2 cm −5 . The background spectral index Γ 2.63 ± 0.02 is compatible with Fermi-LAT observations [5]. Right panel: Expected neutrino fluxes corresponding to muon neutrinos and electron plus tau neutrinos from ≈ 50 TeV DM annihilating into W + W − bosons for an angular field of view of θ = 60 • , 1 • and 0.1 • . The observed atmospheric muon by the IceCube telescope in the 40-string configuration (IC-40) and electron neutrinos by the 79-string configuration (IC-79) are also shown together with the corresponding shared regions at 1σ confidence level [10].
. The cosmological constraints for thermal DM annihilation cross section is given by CMB observation by PLANCK and WMAP satellite experiments among other measurements [8,9]. In the model independent analysis developed here, we assume such value Neutrinos. The differential flux of neutrinos of flavor ν f observed on the Earth can be computed as Eq. (1) with η ν ≡ 3 p=1 P f p . This parameter depends on the dimensions of the source and its distance from the observer: Neutrinos allow directional observation of the GC, although the angular resolution is worse than that for gamma rays. Moreover, it depends on the kind of signal (track or shower) and the position of the source with respect to the horizon of the telescope. All this affects the effective area of the telescope and the possibility to detect a neutrino signal above the background at a given confidence level [10]. The right panel of Fig. 1 shows the detectability of the neutrino signal from ≈ 50 TeV at the GC up the background component, depending on the resolution angle of the telescope. More details on the detectability with 5, 3 and 2σ confidence level may be found in [10].
Antiprotons. As a difference with neutral cosmic-rays that preserve information about the emission direction and spectra, charged cosmic-rays propagation in the Galaxy is a complex process affected by many different physical phenomena: energy losses, convection and reacceleration affect the flux at the Top of Atmosphere (TOA). Due to these effects, the direct observation of antiprotons  produced at the GC is unlikely. The available antiproton data at TOA are in agreement with secondary antiprotons diffusion in the Galaxy [1]. In any case, antiprotons generated at the GC might affect the antiproton flux at the TOA. The prospective flux is given by Eq. (1) with ηp = vp/4π and κ (a) p = ρ (a) R(r , Ep)/M (a) . For DM totally annihilating into W + W − channel the antiproton differential flux at the Solar system is: The diffusion parameter accounts for two different contribution from the Navarro-Frank-White DM halo and the δ-like DM distribution at the GC: The equivalent boost factor normalization constant is given by J NFW ∆Ω ∆Ω HESS D ρ 2 2.13·10 60 m 3 sr [3]. We include in the analysis the solar modulation effect on the antiprotons propagation in the Solar system [4]. It can be neglected for antiprotons production from heavy DM, because the solar modulation affects energies between 1 − 10 GeV [3]. More important is the effect of Galactic wind, that is described as a convective velocity V c . Such velocity at the Galactic disk is V c 0, while at the GC there is evidence of a strong convective velocity of V c 100 − 1000km/s. Such effect reduces the antiproton flux at low energy. In any case, a detailed model of antiproton diffusion at the GC has not been developed so far.

Conclusion
I have reviewed the main results for the study of heavy DM sources at the GC through the observation of different cosmic-rays. The gamma-rays analysis show that HESS and Fermi-LAT data are well RICAP-14 The Roma International Conference on Astroparticle Physics fitted with a ≈ 50 TeV DM candidate annihilating into W + W − , among other channels. The expected neutrino flux from the same source may be detected after an improvement of the resolution angle of current generation of neutrino detectors. Antiprotons observation at higher energies may also set more stringent constraints on the model. Heavy DM candidate with mass of tens of TeV scale is unconstrained so far. Future investigations will be developed in the direction of both indirect and direct searches, DM model building and deeper understanding of the astrophysics at the GC.