A new approach

Supercomputer simulations reveal the effect of the strong nuclear force on the muon’s magnetism.

Credit:
University of Wuppertal

This latest measurement focuses on strong force effects, specifically the “hadronic vacuum polarization,” which arises as quarks and gluons interact within the framework of quantum chromodynamics (QCD) theory. The authors adopted a hybrid approach, combining powerful large-scale computer simulations with experimental data.

“The old methodology involved collecting thousands of experimental results and reinterpreting them to get the single number, the magnetic moment of the muon,” Fodor said. “Our approach was completely different. We divided space-time into very small cells, a lattice, then we solved the equations of the Standard Model on that. There was an awful lot of theory, mathematics, programming, computational knowledge and computer architecture behind this calculation.”

It took 10 years to make those complicated calculations, but when they were done. Fodor et al. found their results agreed with the Standard Model to within half a standard deviation and down to 11 decimal places. It’s the most precise calculation yet achieved, accurate to parts per billion. While the results do not completely rule out possible new physics like a fifth force, they do further constrain the areas where new physics might be lurking.

“People ask me how it feels to make this discovery and, to be honest, I feel somewhat sad,” said Fodor. “When we started to calculate this quantity, we thought we were going to have a good and trustworthy calculation for a new fifth force. Instead, we found there is no fifth force. We did find a very precise proof of not just the Standard Model but also of quantum field theory, which is the foundation on which the Standard Model was built.”

Nature, 2026. DOI: 10.1038/s41586-026-10449-z (About DOIs).