Dark matter and fundamental physics with the Cherenkov Telescope Array Observatory

The Cherenkov Telescope Array Observatory (CTAO) will be the next-generation major ground-based gamma-ray observatory. It will be made up of two large arrays of imaging atmospheric Cherenkov telescopes (IACTs), with one site in the Northern hemisphere (La Palma, Canary Islands) and one in the Southern (Paranal, Chile). CTAO aims to offer great improvement in energetic and angular resolution with respect to current IACT systems, spanning a photon energy range from 20 GeV to 300 TeV, as well as a significantly larger effective area and full-sky coverage. Besides a percentage of observational time available for external proposals, making it the first open gamma-ray observatory, the core observational program of CTAO is organized in several Key Science Projects. A significant amount of time will be devoted to dark matter (e.g. WIMPs, axion-like particles) and fundamental physics studies from a variety of targets, including the Milky Way’s Galactic centre, dwarf spheroidal galaxies, the Large Magellanic Cloud, and extragalactic objects such as blazars. In this contribution, an overview of CTAO’s main features is provided, with a focus on its capabilities to investigate these yet unanswered questions of modern physics.

💡 Research Summary

The paper provides a comprehensive overview of the Cherenkov Telescope Array Observatory (CTAO), emphasizing its role as the next‑generation ground‑based gamma‑ray facility and its potential to address fundamental questions in dark matter and particle physics. CTAO will consist of two sites—one in La Palma (Northern Hemisphere) and one in Paranal (Southern Hemisphere)—each hosting a heterogeneous array of Large‑Sized Telescopes (LSTs, 23 m), Medium‑Sized Telescopes (MSTs, 12 m) and Small‑Sized Telescopes (SSTs, 4 m). This three‑tier design enables continuous coverage from ~20 GeV up to 300 TeV, with the LSTs optimized for low‑energy, faint showers, the MSTs for the core 150 GeV–5 TeV band, and the SSTs for the ultra‑high‑energy regime. Compared with current IACT installations (MAGIC, H.E.S.S., VERITAS), CTAO promises order‑of‑magnitude improvements in energy resolution, angular resolution, and effective area, thereby dramatically increasing sensitivity to weak gamma‑ray signals.

A central component of CTAO’s scientific program is the Key Science Project (KSP) dedicated to dark matter searches. The authors discuss two complementary strategies. The first relies on measuring the continuum gamma‑ray spectrum from regions of high dark‑matter density—principally the Galactic Center (GC), the Large Magellanic Cloud (LMC), the Perseus galaxy cluster, and several dwarf spheroidal galaxies (dSphs). Simulations assuming 825 h of GC exposure predict that CTAO will improve current limits on the velocity‑averaged annihilation cross‑section ⟨σv⟩ for TeV‑scale WIMPs by roughly one order of magnitude. Similar exposures for the LMC (340 h) and Perseus (300 h) yield weaker but still competitive constraints, benefitting from lower astrophysical backgrounds. The second strategy targets spectral lines from direct WIMP annihilation into photon pairs, a signature largely independent of the underlying particle model. Simulated observations of the GC (500 h) and six dSphs (100 h each) indicate that CTAO could set limits on ⟨σv⟩ well below the canonical thermal relic value (3 × 10⁻²⁶ cm³ s⁻¹), potentially reaching sensitivities several orders of magnitude better than present instruments.

Beyond WIMPs, the paper examines the capability of CTAO to probe axion‑like particles (ALPs) and other exotic physics that affect photon propagation over cosmological distances. ALPs, characterized by a mass mₐ and a two‑photon coupling gₐγ, can induce photon↔ALP oscillations in external magnetic fields, leading to energy‑dependent modulations of observed gamma‑ray spectra. The authors simulate 300 h of observations of the AGN NGC 1275 (in the Perseus cluster) in a quiescent state and 10 h during a flare, incorporating realistic turbulent magnetic fields in the cluster and the Milky Way. The resulting constraints on the (mₐ, gₐγ) plane are modest compared with existing limits, but the study highlights that alternative targets or refined analysis techniques could substantially improve sensitivity. Additional simulations suggest that CTAO will also be able to measure the extragalactic background light (EBL), constrain intergalactic magnetic fields, and test Lorentz‑invariance violation through high‑energy AGN observations.

Technologically, the paper notes that prototype LST‑1 is already operational and delivering scientific data, while dual‑mirror SST designs (ASTRI) and the Schwarzschild‑Couder Telescope (SCT) prototypes are being tested in Europe and the United States. Planned upgrades under the Italian PNRR CT A+ project will add two more LSTs and five SSTs to the Southern array, further enhancing performance. Importantly, CTAO will be the first ground‑based gamma‑ray facility to operate as an open observatory, accepting external proposals, yet dedicating roughly 40 % of its first decade’s observing time to internally defined KSPs, with a substantial fraction allocated to dark‑matter and fundamental‑physics investigations.

In conclusion, CTAO represents a revolutionary step forward for very‑high‑energy gamma‑ray astronomy. Its unprecedented sensitivity, broad energy coverage, and full‑sky capability will enable it to set some of the most stringent limits on TeV‑scale dark matter annihilation and decay, and to explore a wide range of beyond‑Standard‑Model phenomena such as ALPs, photon‑photon coupling, and Lorentz‑invariance violation. The simulations presented demonstrate that, within its first ten years, CTAO can improve current WIMP cross‑section limits by at least an order of magnitude and, with optimized strategies, potentially achieve sensitivities far below the thermal relic benchmark. Simultaneously, the observatory’s AGN program will open new windows on cosmological photon propagation, offering complementary probes of fundamental physics. Overall, CTAO is poised to become a cornerstone facility for both astrophysics and particle physics in the coming decade.