Permanent electric dipole moments of particles and atoms
An electron, neutron or nucleus with a built-in electric dipole (a slight separation of its charge along its spin) would break the symmetry between time running forward and backward. Experiments with molecules, atoms and slow neutrons look for this tiny effect.
Why it matters
New sources of time-reversal violation are required to explain why the universe contains matter but not antimatter, and dipole searches probe particles far heavier than colliders reach.
Review
T. E. Chupp, P. Fierlinger, M. J. Ramsey-Musolf, J. T. Singh, Electric dipole moments of atoms, molecules, nuclei, and particles, Reviews of Modern Physics, 2019. https://doi.org/10.1103/RevModPhys.91.015001 reference checked
Timestamp record
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