New insights into the interaction of electromagnetism and the weak nuclear force
Nuclear theorists discovered a major effect of neutron decay related to the interaction of the weak and electromagnetic forces. This discovery changes our understanding of neutron decay and signals the need for high-precision calculations of electromagnetic effects. It also has implications for finding phenomena in the universe that can restore mirror reflection symmetry.
Outside the nucleus, neutrons are unstable particles with a lifetime of about 15 minutes. Neutrons disintegrate due to the weak nuclear force, leaving behind protons, electrons, and antineutrinos. The weak nuclear force is one of the four fundamental forces in the universe, along with the strong, electromagnetic and gravitational forces. Comparison of theoretical predictions based on the weak nuclear force with experimental measurements of neutron decay can reveal hitherto undiscovered interactions. To do this, researchers must achieve a very high level of precision. A team of nuclear theorists has discovered a new and relatively large effect in neutron decay caused by the interaction of the weak and electromagnetic forces.
This study confirmed the change in the intensity with which spinning neutrons experience the weak nuclear force. There are two main meanings here. First, scientists have known since 1956 that systems built as mirror images of systems and systems due to weak forces do not behave the same way. That is, the mirror reflection symmetry is broken. The research has implications for the search for new interactions technically known as “right-handed currents” that restore the mirror reflection symmetry of the universe over very short distances, less than 100 trillionths of a centimeter. Second, this study points to the need to compute electromagnetic effects with higher precision. To do so, you’ll need to use the high-performance computers of the future.
The team calculated the effect of electromagnetic interactions on the decay of neutrons due to the emission and absorption of photons, the quantum of light. The team included nuclear theorists from the Nuclear Theory Laboratory at the University of Washington, North Carolina State University, University of Amsterdam, Los Alamos National Laboratory, and Lawrence Berkeley National Laboratory.
The calculations were performed with a modern method known as “effective field theory” that efficiently constructs the importance of fundamental interactions in phenomena involving strongly interacting particles. The team identified a new percentage-level shift for the nucleon axis-bound gA that governs the decay strength of spinning neutrons. The new corrections come from the emission and absorption of charged pions, the carriers of the strong nuclear force. Effective field theory provides an estimate of the uncertainty, but advanced calculations on the Department of Energy supercomputer are required to improve the current precision. Researchers also evaluated the effect of right-handed currents on retrieval. They found that after incorporating the new calibration, the experimental data and theory agree well and the current uncertainties still allow for new physics at relatively low mass scales.
Reference: “Pion-Induced Radiative Corrections to Neutron β Decay” by Vincenzo Cirigliano, Jordy de Vries, Leendert Hayen, Emanuele Mereghetti and Andre Walker-Loud, 12 Sept. 2022,
This research was supported by the Department of Energy Office of Science, Office of Nuclear Physics; the Laboratory Directed Research and Development program at Los Alamos National Laboratory; the National Science Foundation; and the Dutch Research Council.
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