Earth-ionosphere cavity used to tighten dark matter search limits

Researchers from Kyoto University, Hiroshima University, and Nihon University have utilized the Earth-ionosphere cavity to search for ultralight dark matter, specifically axions. By treating the space between the Earth’s surface and the ionosphere as a natural resonator, the team was able to amplify electromagnetic waves in a way that traditional laboratory magnets, which are limited by physical scale, cannot easily replicate.

Analyzing a decade of geomagnetic data from the British Geological Survey’s Eskdalemuir Observatory, the researchers have placed constraints on ultralight axions approximately 100 times tighter than previous ground-based experiments. The study also identified several unexplained signal candidates that may potentially indicate a dark matter origin.

The team developed a new framework incorporating atmospheric electrical conductivity, allowing for reliable predictions in frequency ranges up to approximately 30 Hz, whereas previous models were largely confined to frequencies below 1 Hz.