No sign of symmetrons yet, physicists report

A high-precision experiment led by TU Wien has set its sights on pinpointing the so-far hypothetical "symmetron fields" using the PF2 ultra-cold neutron source at the Institut Laue-Langevin in France. For the existence of symmetrons could provide an explanation for the mysterious dark energy.

One thing is certain: there's something out there we don't yet know. For years now scientists have been looking for "dark matter" or "dark energy—with our current inventory of particles and forces in nature we just can't explain major cosmological phenomena, such as why the universe is expanding at an ever faster rate.

New theories for "dark energy" have been suggested. One of the candidates is the so-called "symmetron field," which is said to pervade space much like the Higgs field. At the TU Vienna researchers have developed an experiment capable of measuring extremely small forces with the help of neutrons. The measurements were taken during a 100-day campaign at the Institut Laue-Langevin, on its PF2 ultra-cold neutron source. They could have provided pointers to the mysterious symmetrons—but the particles didn't show up. Although this is not the end of the theory, it does at least exclude the possibility of symmetrons existing across a broad range of parameters—and "dark energy" is going to have to be explained differently.