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Scientists are once again grappling with a puzzling phenomenon first observed by the Antarctic Impulsive Transient Antenna (ANITA) project, which recorded unusual radio signals between 2016 and 2018. Unlike typical cosmic rays that travel downward toward Earth, these signals appeared to originate from beneath the Antarctic ice, moving upward a phenomenon that continues to defy explanation.
An international team turned to the Pierre Auger Observatory, the world’s largest cosmic-ray detector, combing through 14 years of data from 2004 to 2018. They searched for events similar to ANITA’s “upward-moving” particle showers.
The results published in Physical Review Letters revealed only a single candidate event, far fewer than expected if the ANITA signals were caused by upward-moving cosmic rays. The discrepancy suggests that the anomaly cannot be easily explained by known physics.
Unlike normal cosmic rays, which descend from space toward Earth, these anomalous signals seem to defy gravity, prompting researchers to explore alternative explanations.
Scientists are exploring several possible explanations for the mysterious upward-moving signals. One possibility involves high-energy tau neutrinos, which could travel through the Earth and produce detectable upward showers upon emerging. Other theories suggest exotic scenarios beyond the Standard Model, such as the presence of sterile neutrinos or interactions involving dark matter.
Researchers are also considering environmental or ice-related effects, which could influence the detection of these unusual signals and potentially create anomalies in the measurements.
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Scientists are developing new balloon missions and specialized detectors to study cosmic particles with greater precision. These missions aim to solve the ANITA mystery and may reveal new insights into the high-energy universe and unknown physics.
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