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We discuss the prospects for indirect detection of dark matter (DM) with the Cherenkov Telescope Array (CTA), a future ground-based gamma-ray observatory that will be sensitive to gamma rays in the energy range from a few tens of GeV to 100 TeV. We consider the detectability of DM annihilation in different astrophysical targets with a focus on the Galactic Center (GC) region. With a deep observation of the GC, CTA will be sensitive to DM particles with mass greater than 100 GeV and an annihilation cross section close to the thermal relic value.
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Over the past decade, extensive studies have been undertaken to search for photon signals from dark matter annihilation or decay for dark matter particle masses above $sim1$ GeV. However, due to the lacking sensitivity of current experiments at MeV-GeV energies, sometimes dubbed the MeV gap, dark matter models with MeV to sub-GeV particle masses have received little attention so far. Various proposed MeV missions (like, e.g., e-ASTROGAM or AMEGO) are aimed at closing this gap in the mid- or long-term future. This, and the absence of clear dark matter signals in the GeV-TeV range, makes it relevant to carefully reconsider the expected experimental instrumental sensitivities in this mass range. The most common two-body annihilation channels for sub-GeV dark matter are to neutrinos, electrons, pions or directly to photons. Among these, only the electron channel has been extensively studied, and almost exclusively in the context of the 511 keV line. In this work, we study the prospects for detecting MeV dark matter annihilation in general in future MeV missions, using e-ASTROGAM as reference, and focusing on dark matter masses in the range 1 MeV-3 GeV. In the case of leptonic annihilation, we emphasise the importance of the often overlooked bremsstrahlung and in-flight annihilation spectral features, which in many cases provide the dominant gamma-ray signal in this regime.
TeV-scale particles that couple to the standard model through the weak force represent a compelling class of dark matter candidates. The search for such Weakly Interacting Massive Particles (WIMPs) has already spanned multiple decades, and whilst it has yet to provide any definitive evidence for their existence, viable parameter space remains. In this paper, we show that the upcoming Cherenkov Telescope Array (CTA) has significant sensitivity to uncharted parameter space at the TeV mass scale. To do so, we focus on two prototypical dark matter candidates, the Wino and Higgsino. Sensitivity forecasts for both models are performed including the irreducible background from misidentified cosmic rays, as well as a range of estimates for the Galactic emissions at TeV energies. For each candidate, we find substantial expected improvements over existing bounds from current imaging atmospheric Cherenkov telescopes. In detail, for the Wino we find a sensitivity improvement of roughly an order of magnitude in $langle sigma v rangle$, whereas for the Higgsino we demonstrate that CTA has the potential to become the first experiment that has sensitivity to the thermal candidate. Taken together, these enhanced sensitivities demonstrates the discovery potential for dark matter at CTA in the 1-100 TeV mass range.
The details of what constitutes the majority of the mass that makes up dark matter in the Universe remains one of the prime puzzles of cosmology and particle physics today - eighty years after the first observational indications. Today, it is widely accepted that dark matter exists and that it is very likely composed of elementary particles - that are weakly interacting and massive (WIMPs for Weakly Interacting Massive Particles). As important as dark matter is in our understanding of cosmology, the detection of these particles has so far been elusive. Their primary properties such as mass and interaction cross sections are still unknown. Indirect detection searches for the products of WIMP annihilation or decay. This is generally done through observations of gamma-ray photons or cosmic rays. Instruments such as the Fermi-LAT, H.E.S.S., MAGIC and VERITAS, combined with the future Cherenkov Telescope Array (CTA) will provide important and complementary constraints to other search techniques. Given the expected sensitivities of all search techniques, we are at a stage where the WIMP scenario is facing stringent tests and it can be expected that WIMPs will be either be detected or the scenario will be so severely constrained that it will have to be re-thought. In this sense we are on the Threshold of Discovery. In this article, I will give a general overview over the current status and the future expectations for indirect searches for dark matter (WIMP) particles.
In this white paper, submitted as a part of Snowmass 2013 (subgroup CF2), we examine the current status and future prospects of the VERITAS indirect dark matter detection program. The VERITAS array of imaging atmospheric Cherenkov telescopes (IACTs), sensitive in the 0.1-50 TeV regime, is in the process of completing a multi-year program aimed at detecting signatures of neutralino dark matter. This program is spread out over a range of astrophysical targets which can potentially yield definitive signatures of neutralino self-annihilation such as dwarf spheroidal galaxies (dSphs) and the center of the Milky Way galaxy. While the program is still in progress, initial results on dSphs have produced very competitive upper limits on the thermally averaged cross-section of neutralino self-annihilation as well as strongly constraining leptophillic dark matter models (such as those inferred from the PAMELA and AMS positron fraction results). As the program continues over the next 5 years, VERITAS observations will yield some of the strongest constraints available from IACTs, pushing down the limit on the thermally averaged cross-section of neutralino self-annihilation to the expected natural thermal relic scale.
The self-annihilation of dark matter particles with mass in the MeV range can produce gamma rays via prompt or secondary radiation. The annihilation rate for such light dark matter particles is however tightly constrained by cosmic microwave background (CMB) data. Here we explore the possibility of discovering MeV dark matter annihilation with future MeV gamma-ray telescopes taking into account the latest and future CMB constraints. We study the optimal energy window as a function of the dominant annihilation final state. We consider both the (conservative) case of the dwarf spheroidal galaxy Draco and the (more optimistic) case of the Galactic center. We find that for certain channels, including those with one or two monochromatic photon(s) and one or two neutral pion(s), a detectable gamma-ray signal is possible for both targets under consideration, and compatible with CMB constraints. For other annihilation channels, however, including all leptonic annihilation channels and two charged pions, CMB data rule out any significant signal of dark matter annihilation at future MeV gamma-ray telescopes from dwarf galaxies, but possibly not for the Galactic center.
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