TeV DM – DAMASCO

5 February, 20215 February, 2021

Sensitivity of the Cherenkov Telescope Array to dark subhalos

Written by Javier Coronado-Blázquez.

Summary of the paper with the same title submitted to PDU.

In this work, we study the potential of the Cherenkov Telescope Array (CTA) for the detection of Galactic dark matter (DM) subhalos, focusing on low-mass subhalos – not massive enough to retain any baryonic content – therefore lacking any multiwavelength counterpart. As in previous papers, devoted to the Fermi-LAT and HAWC instruments, If the DM is made of weakly interacting massive particles (WIMPs), these dark subhalos may appear in the gamma-ray sky as unidentified sources. We perform a detailed characterization of CTA instrumental response to dark subhalos, using the ctools analysis software, simulating CTA observations under different array configurations and pointing strategies.

We distinguish three different observational modes: i) a key science project, the extragalactic survey (codename EGAL). This will observe a fourth of sky at high-latitudes with uniform exposure, providing unprecedented coverage at very high energies; ii) a proposed deep-field campaign (DEEP), which would point at a blank spot of the sky aiming to serendipitously find new sources, such as dark subhalos, due to the extreme sensitivity; and iii) a chance of finding a dark subhalo in the field of view of any of CTA’s science operations through accumulated exposure the years, so-called overall exposure (EXPO).

To be able to compute the latter strategy, one has to estimate the sky coverage in, e.g., 10 years of operation, as well as the median exposure time. We did so by extrapolating the MAGIC telescope operations, which share location with the CTA-North. In this way, we get a realistic estimation of the accumulated observations, which turn out to be a factor 2 more area and a factor 10 more time than the EGAL survey. This, together with information on the subhalo population as inferred from N-body cosmological simulations, allows us to predict the CTA detectability of dark subhalos, i.e., the expected number of subhalos in each of the considered observational scenarios.

In the absence of detection, for each observation strategy we set competitive limits to the annihilation cross section as a function of the DM particle mass, that are between one and two orders of magnitude away from the thermal cross section, for the bb and ττ annihilation channels. This way, CTA will offer the most constraining limits from subhalo searches in the intermediate range between 1−3 TeV, complementing previous results with Fermi-LAT and HAWC at lower and higher energies, respectively, as well as an independent probe of DM.

10 July, 20209 September, 2020

CTA sensitivity to branon dark matter models

Written by Alejandra Aguirre-Santaella.

Summary of the paper with the same title accepted by JCAP.

arXiv: 2006.16706

TeV dark matter (DM) candidates are gradually earning more and more attention within the community, since there is no clear hint of DM signals in the GeV regime so far. One of these particles are branons, which could be detected with the next generation of very-high-energy gamma-ray observatories such as the Cherenkov Telescope Array (CTA).

Branons represent the vibrations of branes embedded into a higher dimensional space-time. These DM particles are WIMPs that may annihilate into e.g. a pair of quarks, a pair of weak bosons, or even a pair of photons, yet the probability for the latter to occur is extremely low. The branching ratio of annihilation into each SM channel depends on the mass of the branons and the tension of the brane. In case branons are considered thermal relics and their annihilation cross-section value is the one needed to account for 100% of the total DM content of the Universe, the tension is a function of the branon mass, and we are left with only one free parameter.

In this work, we study the sensitivity of CTA to branon DM via the observation of representative astrophysical DM targets, namely dwarf spheroidal galaxies. In particular, we focus on two well-known ones, Draco on the Northern Hemisphere and Sculptor on the Southern Hemisphere. For each of these targets, we simulated 300 h of CTA observations and studied the sensitivity of both CTA-North and CTA-South to branon annihilations using the latest publicly available instrument response functions and most recent analysis tools.

We computed annihilation cross section values needed to reach a 5σ detection as a function of the branon mass. Additionally, in the absence of a predicted DM signal, we obtained 2σ upper limits on the annihilation cross section. Our limits lie 1.5-2 orders of magnitude above the thermal relic cross section value, depending on the considered branon mass.

Yet, CTA will allow to exclude a significant portion of the brane tension-mass parameter space in the 0.1-60 TeV branon mass range, and up to tensions of ~10 TeV. More importantly, CTA will significantly enlarge the region already excluded by AMS and CMS, and will provide valuable complementary information to future SKA radio observations. We conclude that CTA will possess potential to constrain brane-world models and, more in general, TeV DM candidates.

20 February, 202020 February, 2020

SKA-Phase 1 sensitivity to synchrotron radio emission from multi-TeV Dark Matter candidates

Written by V. Gammaldi and M. Méndez-Isla.

Summary of the paper with the same title published in PDU.

arXiv: 1905.11154

Dark matter constitutes a fundamental piece within the paradigm of modern Cosmology, comprising ~25% of the energy density of the universe. Despite numerous evidence of the existence of dark matter, its nature remains elusive. Based on the study of thermal relics in the Early Universe, one possibility would be conceiving dark matter as particles. Indeed, the energy density of dark matter today could be explained in terms of Weakly Interactive Massive Particles that were coupled with the primordial plasma.

Considering dark matter annihilating in galactic halos, it would be reasonable to expect signatures in the sky that may be observed through different detectors. This fact would allow us to constrain the dark matter parameter space comparing theoretical predictions with diverse observational data. In fact, there exists the possibility of dark matter annihilating into Standard Model particles that subsequently would decay or hadronise into cosmic rays. In this scenario, dark matter not only would constitute an exotic source of cosmic rays but also of photons in a large range of frequencies. Such photons are the result of the interaction of the abovementioned cosmic rays with the interstellar medium. Indeed, one possibility could be dark matter annihilating into electrons/positrons whose interaction with galactic magnetic fields would produce synchrotron signals, in general, at radio frequencies. In this sense, high-sensitivity radio telescopes, such as the Square Kilometre Array, could be crucial to put tight constraints on both the dark matter mass M and its thermally averaged cross section.

With the purpose of constraining radio signals from TeV dark matter candidates with SKA, we compute the expected flux density for different annihilation channels in the Draco dwarf spheroidal galaxy and we compare it with the SKA sensitivity. Varying the dark matter mass M and thermally averaged cross section, we set sensitivity constraints, as shown in the Figure below. In such a Figure, the region above the orange and blue curves show the dark matter parameter space detectable by the SKA. Furthermore, the intersection between the orange curve and the dashed black line representing a cross section of 3e26 cm^3 / s shows that the maximum observable mass for thermal relics would lie around 10 TeV for dark matter annihilating into W+W- and b quarks.

A similar analysis is performed for extra-dimensional Brane-world DM candidates, dubbed branons, i.e., new degrees of freedom appearing in flexible Brane-world models. This particular case is analysed for usual astrophysical scenarios as well as alternative ones in which the synchrotron signal would be enhanced by the presence of an intermediate-mass black hole. This latter possibility could be the key to observe dark matter masses beyond the 10 TeV detectable in conventional scenarios.

Finally, we compare the SKA facilities in dark matter searches with other detectors for different ranges of frequencies. Even though SKA is expected to be the most sensitivity telescope in radio frequencies, the most suitable frequency range to detect dark matter would be affected by the annihilation channel. In this regard, in our work we also analyse the role played by detectors such as GBT, VLA or LOFAR for TeV dark matter multi-wavelength searches.