Viviana Gammaldi

Possible dark matter origin of the gamma ray emission from the Galactic Center observed by HESS

We show that the gamma ray spectrum observed with the HESS array of Cherenkov telescopes coming from the Galactic Center region and identified with the source HESS J1745-290 is well fitted by the secondary photons coming from dark matter (DM) annihilation over a diffuse power law background. The amount of photons and morphology of the signal localized within a region of few parsecs, require compressed DM profiles as those resulting from baryonic contraction, which offer 103 enhancements in the signal over DM alone simulations. The fitted background from HESS data is consistent with recent Fermi-LAT observations of the same region.

Detection of branon dark matter with gamma ray telescopes

Branons are new degrees of freedom that appear in flexible brane-world models corresponding to brane fluctuations. These new fields can behave as standard weakly interacting massive particles (WIMPs) with a significant associated thermal relic density. We analyze the present constraints from their spontaneous annihilations into photons for Energetic Gamma-Ray Experiment Telescope (EGRET), Fermi Large Area Telescope (LAT), and Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC) telescopes, and the prospects for detection in future Cherenkov telescopes. In particular, we focus on possible signals coming from the Galactic center and different dwarf spheroidals, such as Draco, Sagittarius, Canis Major and SEGUE 1. We conclude that for those targets, present observations are below the sensitivity limits for branon detection by assuming standard dark matter distributions and no additional boost factors. However, future experiments such as the Cherenkov Telescope Array (CTA) could be able to detect gamma-ray photons coming from the annihilation of branons with masses higher than 150 GeV.

Spectral study of the HESS J1745-290 gamma-ray source as dark matter signal

We study the main spectral features of the gamma-ray fluxes observed by the High Energy Stereoscopic System (HESS) from the J1745-290 Galactic Center source during the years 2004, 2005 and 2006. In particular, we show that these data are 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. We present explicit analyses for annihilation in a single standard model particle-antiparticle pair. In this case, the best fits are obtained for the u (u) over bar and d (d) over bar quark channels and for the W+W- and ZZ gauge bosons, with background spectral index compatible with the Fermi-Large Area Telescope (LAT) data from the same region. The fits return a heavy WIMP, with a mass above similar to 10 TeV, but well below the unitarity limit for thermal relic annihilation.

Reliability of Monte Carlo event generators for gamma-ray dark matter searches

A bstractWe study the differences in the gamma-ray spectra simulated by four Monte Carlo event generator packages developed in particle physics. Two different versions of PYTHIA and two of HERWIG are analyzed, namely PYTHIA 6.418 and HERWIG 6.5.10 in Fortran and PYTHIA 8.165 and HERWIG 2.6.1 in C++. For all the studied channels, the intrinsic differences between them are shown to be significative and may play an important role in misunderstanding dark matter signals.

Antiproton signatures from astrophysical and dark matter sources at the galactic center

The center of our Galaxy is a complex region characterized by extreme phenomena. The presence of the supermassive Sagittarius A* black hole, a high Dark Matter density and an even higher baryonic density are able to produce very energetic processes. Indeed, high energetic gamma rays have been observed by different telescopes, although its origin is not clear. In this work, we constrain the possible antiproton flux component associated to this signal. The expected secondary astrophysical antiproton background already saturates the observed data. It implies that any other important astrophysical source leads to an inconsistent excess, since the theoretical uncertainties corresponding to the mentioned background are small. The constraints depend on the diffusion model and the spectral features of the source. In particular, we consider antiproton spectra described by a power-law, a monochromatic signal and a Standard Model particle-antiparticle channel production.

Neutrino fluxes from Dark Matter in the HESS J1745-290 source at the Galactic Center

The spectral study of the HESS J1745-290 high-energy gamma-ray cutoff from the Galactic center is compatible with a signal of dark matter (DM) annihilation or decay. If this is the case, a neutrino flux from that source is also expected. We analyze the neutrino flux predicted by DM particles able to create the HESS J1745-290 gamma-rays observations. We focus on the electroweak and hadronic channels, which are favored by present measurements. In particular, we study DM annihilating into W+W- and u (u) over bar with DM masses of 48.8 and 27.9 TeV, respectively. We estimate the resolution angle and exposition time necessary to test the DM hypothesis as the origin of the gamma-ray signal.

Analysis of the very inner Milky Way dark matter distribution and gamma-ray signals

We analyze the possibility that the HESS γ-ray source at the Galactic center could be explained as the secondary flux produced by annihilation of TeV dark matter (DM) particles with locally enhanced density, in a region spatially compatible with the HESS observations themselves. We study the inner 100 pc considering (i) the extrapolation of several density profiles from state-of-the-art N-body þ hydrodynamics simulations of Milky Way-like galaxies, (ii) the DM spike induced by the black hole, and (iii) the DM particles scattering off by bulge stars. We show that in some cases the DM spike may provide the enhancement in the flux required to explain the cutoff in the HESS J1745-290γ-ray spectra as TeV DM. In other cases, it may help to describe the spatial tail reported by HESS II at angular scales ≲0.54° toward Sgr A*.

Indirect constraints to branon dark matter

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. Here we briefly review the present constraints for the detection of gamma ray photons produced in the annihilation of branon dark matter. We show that observations of dwarf spheroidal galaxies and the galactic center by EGRET, Fermi-LAT or MAGIC are below the sensitivity limits for branon detection. However, future experiments such as CTA could be able to detect gamma-ray photons from annihilating branons of masses above 150 GeV.

Cosmic Rays from Heavy Dark Matter from the Galactic Center

The gamma-ray fluxes observed by the High Energy Stereoscopic System (HESS) from the J1745-290 Galactic Center source is well fitted by the secondary photons coming from Dark Matter (DM) annihilation in particle-antiparticle standard model pairs over a diffuse power-law background. The spectral features of the signal are consistent with different channels: light quarks, electro-weak gauge bosons and top-antitop production. The amount of photons and morphology of the signal localized within a region of few parsecs, require compressed DM profiles as those resulting from baryonic contraction, which offer large enhancements in the signal over DM alone simulations. The fits return a heavy WIMP, with a mass above 10 TeV, but well below the unitarity limit for thermal relic annihilation. The fitted background spectral index is compatible with the Fermi-Large Area Telescope (LAT) data from the same region. This possibility can be potentially tested with the observations of other high energy cosmic rays.