Tentative observation of a gamma-ray line at the Fermi LAT

Using 43 months of public gamma-ray data from the Fermi Large Area Telescope, we find in regions close to the Galactic center at energies of 130 GeV a 4.6 sigma excess that is not inconsistent with a gamma-ray line from dark matter annihilation. When taking into account the look-elsewhere effect, the significance of the observed signature is 3.2 sigma. If interpreted in terms of dark matter particles annihilating into a photon pair, the observations imply a partial annihilation cross-section of about 10^-27 cm^3s^-1 and a dark matter mass around 130 GeV. We review aspects of the statistical analysis and comment on possible instrumental indications.Comment: 4 pages, 5 figures, Proceedings of the 5th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2012

Gamma Ray Signals from Dark Matter: Concepts, Status and Prospects

Weakly interacting massive particles (WIMPs) remain a prime candidate for the cosmological dark matter (DM), even in the absence of current collider signals that would unambiguously point to new physics below the TeV scale. The self-annihilation of these particles in astronomical targets may leave observable imprints in cosmic rays of various kinds. In this review, we focus on gamma rays which we argue to play a pronounced role among the various possible messengers. We discuss the most promising spectral and spatial signatures to look for, give an update on the current state of gamma-ray searches for DM and an outlook concerning future prospects. We also assess in some detail the implications of a potential signal identification for particle DM models as well as for our understanding of structure formation. Special emphasis is put on the possible evidence for a 130 GeV line-like signal that was recently identified in the data of the Fermi gamma-ray space telescope.Comment: 42 pages, 6 figures, 2 tables; updated reference list and extended discussio

Indirect Searches for Decaying Dark Matter

Numerous observations point towards the existence of an unknown elementary particle with no electromagnetic interactions, a large population of which was presumably produced in the early stages of the history of the Universe. This so-called dark matter has survived until the present day, accounting for the 26% of the present energy budget of the Universe. It remains an open question whether the particles comprising the dark matter are absolutely stable or whether they have a finite but very long lifetime, which is a possibility since there is no known general principle guaranteeing perfect stability. In this article we review the observational limits on the lifetime of dark matter particles with mass in the GeV-TeV range using observations of the cosmic fluxes of antimatter, gamma-rays and neutrinos. We also examine some theoretically motivated scenarios that provide decaying dark matter candidates.Comment: 47 pages, 11 figures, 6 tables. Invited review for the International Journal of Modern Physics A. Matches published versio

A Fresh Approach to Forecasting in Astroparticle Physics and Dark Matter Searches

We present a toolbox of new techniques and concepts for the efficient forecasting of experimental sensitivities. These are applicable to a large range of scenarios in (astro-)particle physics, and based on the Fisher information formalism. Fisher information provides an answer to the question what is the maximum extractable information from a given observation?. It is a common tool for the forecasting of experimental sensitivities in many branches of science, but rarely used in astroparticle physics or searches for particle dark matter. After briefly reviewing the Fisher information matrix of general Poisson likelihoods, we propose very compact expressions for estimating expected exclusion and discovery limits (equivalent counts method). We demonstrate by comparison with Monte Carlo results that they remain surprisingly accurate even deep in the Poisson regime. We show how correlated background systematics can be efficiently accounted for by a treatment based on Gaussian random fields. Finally, we introduce the novel concept of Fisher information flux. It can be thought of as a generalization of the commonly used signal-to-noise ratio, while accounting for the non-local properties and saturation effects of background and instrumental uncertainties. It is a powerful and flexible tool ready to be used as core concept for informed strategy development in astroparticle physics and searches for particle dark matter.Comment: 33 pages, 12 figure

Strong support for the millisecond pulsar origin of the Galactic center GeV excess

Using gamma-ray data from the Fermi Large Area Telescope, various groups have identified a clear excess emission in the Inner Galaxy, at energies around a few GeV. This excess resembles remarkably well a signal from dark-matter annihilation. One of the most compelling astrophysical interpretations is that the excess is caused by the combined effect of a previously undetected population of dim gamma-ray sources. Because of their spectral similarity, the best candidates are millisecond pulsars. Here, we search for this hypothetical source population, using a novel approach based on wavelet decomposition of the gamma-ray sky and the statistics of Gaussian random fields. Using almost seven years of Fermi-LAT data, we detect a clustering of photons as predicted for the hypothetical population of millisecond pulsar, with a statistical significance of 10.0 sigma. For plausible values of the luminosity function, this population explains 100% of the observed excess emission. We argue that other extragalactic or Galactic sources, a mismodeling of Galactic diffuse emission, or the thick-disk population of pulsars are unlikely to account for this observation.Comment: 6+10 pages, 3+10 figures, 1 table; v2 updated to pass 8 Fermi data, additional supplemental material with extended discussion (conclusions unchanged); v3 matches PRL version with further checks (conclusions unchanged

The GeV Excess Shining Through: Background Systematics for the Inner Galaxy Analysis

Recently, a spatially extended excess of gamma rays collected by the Fermi-LAT from the inner region of the Milky Way has been detected by different groups and with increasingly sophisticated techniques. Yet, any final conclusion about the morphology and spectral properties of such an extended diffuse emission are subject to a number of potentially critical uncertainties, related to the high density of cosmic rays, gas, magnetic fields and abundance of point sources. We will present a thorough study of the systematic uncertainties related to the modelling of diffuse background and to the propagation of cosmic rays in the inner part of our Galaxy. We will test a large set of models for the Galactic diffuse emission, generated by varying the propagation parameters within extreme conditions. By using those models in the analysis of Fermi-LAT data as Galactic foreground, we will show that the gamma-ray excess survives and we will quantify the uncertainties affecting the excess morphology and energy spectrum.Comment: 2014 Fermi Symposium proceedings - eConf C14102.1 7 pages, 4 figure

The role of the eROSITA all-sky survey in searches for sterile neutrino dark matter

We investigate for the first time the potential of angular auto- and cross-correlation power spectra in identifying sterile neutrino dark matter in the cosmic X-ray background. We take as reference the performance of the soon-to-be-launched eROSITA satellite. The main astrophysical background sources against sterile neutrino decays are active galactic nuclei, galaxies powered by X-ray binaries, and clusters of galaxies. While sterile neutrino decays are always subdominant in the auto-correlation power spectra, they can be efficiently enhanced when cross-correlating with tracers of the dark matter distribution such as galaxies in the 2MASS catalogues. We show that the planned four-years eROSITA all-sky survey will provide a large enough photon statistics to potentially yield very stringent constraints on the decay lifetime, enabling to firmly test the recently claimed 3.56-keV X-ray line found towards several clusters and galaxies and its decaying dark matter interpretation. However, we also show that in order to fully exploit the potential of eROSITA for dark matter searches, it is vital to overcome the shot-noise limitations inherent to galaxy catalogues as tracers for the dark matter distribution.Comment: 26 pages, 12 figures, version accepted by JCA

Updated cosmic-ray and radio constraints on light dark matter: Implications for the GeV gamma-ray excess at the Galactic center

The apparent gamma-ray excess in the Galactic center region and inner Galaxy has attracted considerable interest, notably because both its spectrum and radial distribution are consistent with an interpretation in terms of annihilating dark matter particles with a mass of about 10-40 GeV. We confront such an interpretation with an updated compilation of various indirect dark matter detection bounds, which we adapt to the specific form required by the observed signal. We find that cosmic-ray positron data strongly rule out dark matter annihilating to light leptons, or 'democratically' to all leptons, as an explanation of the signal. Cosmic-ray antiprotons, for which we present independent and significantly improved limits with respect to previous estimates, are already in considerable tension with DM annihilation to any combination of quark final states; the first set of AMS-02 data will thus be able to rule out or confirm the DM hypothesis with high confidence. For reasonable assumptions about the magnetic field in the Galactic center region, radio observations independently put very severe constraints on a DM interpretation of the excess, in particular for all leptonic annihilation channels.Comment: 23 pages revtex, 19 figures, 1 table. Extended discussion of antiproton limits and added references. Matches published versio