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Unknown forces could be hiding in the values of fundamental constants

11 April 2023
The values of fundamental constants of nature might be affected by new particles and unknown forces of nature, according to a study by an international group of scientists, including physicist Jeroen Koelemeij of VU Amsterdam.

The scientists investigated the standard model of particle physics, which predicts how elementary particles behave, interact, and eventually form larger structures such as atomic nuclei, atoms, and molecules. This model includes the values of fundamental constants of nature, such as the mass of the electron and the speed of light. The results of some recent experiments hint towards behaviour that might be explained by new particles or unknown forces of nature. The scientists have examined six possible new-physics models that postulate, for example, the existence of particles akin to the famed Higgs boson. All findings were published in the journal Physical Review Letters.

Unknown forces
The values of the fundamental constants are adjusted every few years by the Committee on Data for Science and Technology (CODATA) so that the theoretical predictions of the standard model of particle physics match experimental results as closely as possible. Recent CODATA adjustments revealed that some experimental data are not fully consistent with the found fundamental constants. Koelemeij: “This problem was mitigated by increasing the uncertainty of these experimental data so that the inconsistency became insignificant, but there is also a possibility that the inconsistency was due to new physical phenomena. This is because the standard model is no longer valid as soon as there is one particle or force that could exist outside the standard model."

Possible new-physics models
In their study, the scientists modify the CODATA adjustment by adding the hypothetical effect of a new particle to the standard model predictions. The theory that describes this new particle is then characterized by its own fundamental constants, for example the mass of the new particle. In one of the six possible new-physics models they investigated, the introduction of a new particle made the inconsistencies disappear. The new particle also caused the values of some of the existing fundamental constants to change substantially from their present CODATA values.

Still, the scientists stress that their results should not be construed as the discovery of a new particle. They point at measurement data from particle accelerator experiments that rule out some of the hypothetical models that they proposed. Nevertheless their work provides a novel, consistent way of incorporating fundamental constants in models that attempt to explain possible new physics. As such their work might ultimately help answer the question what unknown physics lies beyond the standard model.

Image: camera image from one of the precision experiments that were included in the study: collection of laser-cooled of atoms and molecules, whose properties have been studied both experimentally and theoretically with very high precision in search for traces of new particles or forces.