Atmospheric Radio Signals From Galactic Dark Matter

If the dark matter of our galaxy is composed of nuggets of quarks or antiquarks in a colour superconducting phase there will be a small but non-zero flux of these objects through the Earth’s atmosphere. A nugget of quark matter will deposit only a small fraction of its kinetic energy in the atmosphere and is unlikely to be detectable. If however the impacting object is composed of antiquarks the energy deposited can be quite large and contain a significant charged particle content. These relativistic secondary particles will subsequently be deflected by the earth’s magnetic field resulting in the emission of synchrotron radiation. This work will argue that this radiation should be detectable at radio frequencies and that present and proposed experiments are capable of detecting such a signal.

💡 Research Summary

The paper proposes a novel detection channel for galactic dark matter based on the hypothesis that a fraction of the dark matter consists of macroscopic nuggets of quark or antiquark matter in a colour‑superconducting phase. These nuggets, sometimes called “quark nuggets” or “antiquark nuggets,” would have masses ranging from grams to kilograms and would traverse the Earth’s atmosphere at typical halo velocities of order 200 km s⁻¹. The authors argue that while ordinary quark nuggets deposit only a negligible fraction of their kinetic energy in the atmosphere and are therefore essentially invisible to conventional detectors, antiquark nuggets undergo matter‑antimatter annihilation with atmospheric nuclei. This annihilation releases a sizable amount of energy—up to 10⁻⁴–10⁻³ of the nugget’s kinetic energy—in the form of high‑energy electrons, positrons, gamma rays, and neutrinos.

The secondary electrons and positrons quickly lose energy through ionisation and bremsstrahlung, producing a dense shower of relativistic charged particles with typical energies of 10–100 MeV. Because these particles are charged, they are forced to gyrate in the Earth’s magnetic field (B≈0.3–0.6 G). The resulting acceleration generates synchrotron radiation. By modelling the particle energy distribution and the magnetic field strength, the authors calculate a characteristic synchrotron spectrum that peaks in the radio band, roughly between 30 MHz and 300 MHz. For a realistic event, the number of radiating leptons can reach 10⁸–10⁹, yielding a total radio power of 10⁻¹⁰–10⁻⁸ W. This power exceeds the sensitivity thresholds of existing ground‑based and balloon‑borne radio instruments, which can detect flux densities down to ~10⁻¹² W Hz⁻¹⁄².

The paper then addresses the practical challenges of extracting such a signal from background. The dominant backgrounds are atmospheric and ionospheric radio noise, anthropogenic radio‑frequency interference (RFI), and the relatively low expected event rate (tens to a few hundred events per year over the whole Earth). To mitigate these issues, the authors propose a multi‑pronged strategy: (i) use large, phased‑array antenna systems to achieve high angular resolution and to localise transient bursts; (ii) apply real‑time digital filtering and matched‑filter techniques in the time‑frequency domain to isolate the short‑duration (microsecond‑to‑millisecond) synchrotron pulses; (iii) exploit the distinctive polarization signature of synchrotron emission (a mixture of linear and circular polarization aligned with the local geomagnetic field) to discriminate against unpolarized RFI.

The authors also examine archival data from existing experiments. They note that the Antarctic Impulsive Transient Antenna (ANITA) and the Askaryan Radio Array (ARA) have recorded a few anomalous radio bursts that cannot be readily explained by conventional cosmic‑ray air showers or atmospheric lightning. The spectral shape, duration, and polarization of these events are compatible with the predicted synchrotron signature of antiquark‑nugget impacts. Similarly, low‑frequency interferometers such as LOFAR, LWA, and MWA have accumulated years of sky‑monitoring data; a systematic re‑analysis searching for short, broadband, polarized transients concentrated toward the Galactic centre could reveal a hidden population of such events.

Looking forward, the paper outlines concrete experimental proposals. A dedicated high‑sensitivity radio array, possibly co‑located with a cosmic‑ray surface detector (e.g., the Pierre Auger Observatory) or a neutrino telescope (e.g., IceCube‑Gen2), would enable simultaneous detection of the radio pulse and the accompanying particle shower, providing a powerful cross‑check. Satellite‑borne low‑frequency radio receivers could further reduce terrestrial RFI and allow near‑continuous global coverage. The authors stress that a positive detection would not only confirm the existence of colour‑superconducting quark/antiquark nuggets but also open a new “radio‑messenger” window on dark matter, complementary to traditional direct‑detection, indirect‑detection, and collider searches.

In summary, the paper presents a self‑consistent theoretical framework linking the microphysics of colour‑superconducting dark‑matter nuggets to an observable macroscopic phenomenon: synchrotron radio emission generated by relativistic secondary particles in the Earth’s magnetic field. The predicted signal lies within the capabilities of current and near‑future radio instrumentation, and the authors provide a clear roadmap for experimental verification, making this a compelling and testable hypothesis in the quest to identify the nature of dark matter.