What does "Cabibbo Angle Anomaly" mean?
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The Cabibbo angle anomaly is a term used in particle physics. It refers to a strange finding in measurements related to how certain particles, called quarks, interact. Normally, these interactions follow specific rules, known as unitarity conditions, which should hold true. However, recent studies show that there is a significant discrepancy, known as a $3\sigma$ level deficit, specifically in the first-row interactions of quarks.
Implications
This anomaly suggests that something unusual might be happening beyond our current understanding of particle physics. Scientists are looking into possible explanations, including the idea of new types of particles. Two main theories have emerged: one involves heavy vector-like quarks, and the other suggests the existence of a very light particle called a MeV sterile neutrino.
MeV Sterile Neutrino
The MeV sterile neutrino is a hypothetical particle that doesn't interact like regular particles we know. It could mix with electron-type neutrinos and affect measurements in a way that helps explain the Cabibbo angle anomaly. Although this particle could influence certain types of nuclear decay processes, it appears to leave other measurements mostly unchanged. Researchers are examining how this idea might fit into existing theories about neutrinos and their roles in the universe.