Abstract

It is widely accepted that dark matter makes up about 80% of the matter content in the Universe. Its particle nature is however completely unknown yet, and revealing it will lead to a major breakthrough in physics [1,2]. A promising approach for achieving this goal is to look for gamma-ray signatures through dark matter annihilation or decay. These gamma rays would be detected by space-based instruments like the Large Area Telescope on board the Fermi Gamma-ray Satellite (Fermi -LAT) or by ground-based observatories like VERITAS, MAGIC, H.E.S.S. or the next-generation Cherenkov Telescope Array (CTA) probably to be constructed in Chile. It is worth mentioning that a group of Chilean institutions, including the Pontificia Universidad Cat´olica de Chile, have become part of the CTA Consortium. A detection of gamma rays from dark matter would not only confirm the existence of dark matter through a non-gravitational force, but also indicate the existence of physics beyond the Standard Model. Regions in the cosmos of large dark matter concentration, like the Galactic Center or dwarf spheroidal galaxies, are the most promising targets for catching a gamma-ray signal. The center of the Milky Way is the most interesting but also complicated region of the gamma-ray sky because of the many point sources and the uncertainties associated with the diffuse gamma-ray emission. Many independent groups have claimed to find an unaccounted excess over conventional diffuse backgrounds, compatible with dark matter predictions, in the data collected by the Fermi -LAT from the Galactic Center in the GeV energy range [15-20]. These claims are based on the modelling of known gamma-ray sources and their subtraction from data. However, at few GeVs the modelling of gamma-ray emitters in the line of sight of the Milky Way’s center is full of uncertainties [21]. This proposal is aimed at two main objetives. The first of these is to perform a marginalisation of background and foreground models using Fermi -LAT data and a plethora of models in order to determine the spectrum and morphology of the putative Galactic Center gamma-ray excess. Then, to study the possible phenomena able to account for the excess and test their implications for other experiments and/or observations. Although we focus on dark matter annihilation and decay as explanation of the excess, we will explore other possibilities, such as a population of yet unresolved millisecond pulsars located in the bulge of the Milky Way, and secondary emission from cosmic-ray protons or electrons injected in the Galactic Center by past bursts. We expect that a comprehensive study of these phenomena will predict features that can be tested in observations at other wavelengths, in direct detection experiments, and/or the LHC. The second objetive of this proposal aims to be part of the Chilean contribution to the Dark Matter and Fundamental Physics group of the CTA Consortium. The CTA will consist of two arrays, a smaller one in the Northern Hemisphere and the main one in the South, the later of which will concentrate on Galactic sources. We propose to carry out simulations of CTA observations of the Galactic Center. As the sensitivity of CTA to different dark matter fundamental properties depends on the observation strategy, the simulations will explore well-motivated dark-matter parameter space to choose the CTA configuration and strategy that optimally discerns between dark matter signatures and other gamma-ray emitters. The outcome of this part of the proposal will be sensitivity of the generated mock data to the detection of different dark matter candidates and distributions. Finally, one side objetive of this project is to push forward the particle astrophysics field in Chile creating collaborations among astronomers and particle physicists, in order to contribute significantly to the worldwide effort to identify the nature of the dark matter.