A team of physicists has released tantalizing evidence claiming that there may be a fifth force of nature, according to a paper published in Physical Review Letters.
"If true, it's revolutionary," said Jonathan Feng, lead author of the study and professor of physics and astronomy at the University of California, Irvine.
"For decades, we've known of four fundamental forces: gravitation, electromagnetism, and the strong and weak nuclear forces. If confirmed by further experiments, this discovery of a possible fifth force would completely change our understanding of the universe, with consequences for the unification of forces and dark matter."
The study builds upon previous research by a group of experimental nuclear physicists at the Hungarian Academy of Sciences. They stumbled across an anomaly when inspecting the radioactive decay of an unstable isotope of beryllium for any sign of "dark photons" – a dark matter particle.
No "dark photons" were found, unfortunately, but the Hungarian physicists did manage to find traces of a new particle that is around 30 times heavier than the electron.
The physicists from UCI analysed the data in further detail to try and work out what type of particle it could be. It's certainly not a dark photon, but it's not a particle associated with matter either, the physicists found. Instead, they believe it could be a force carrier – the "protophobic X boson" or "X boson."
The X boson interacts only with electrons and neutrons over a tiny distance – only 14 femtometres (10‑15 m).
Timothy Tait, co-author of the paper and particle physicist at UCI, said: "There's no other boson that we've observed that has this same characteristic. Sometimes we also just call it the 'X boson,' where 'X' means unknown."
The physicists reckon the mass of the X boson is pretty light – smaller than the Higgs boson – and should be able to be seen in laboratory experiments. It quickly decays into a positron and electron.
"But the reason it's been hard to find is that its interactions are very feeble. That said, because the new particle is so light, there are many experimental groups working in small labs around the world that can follow up the initial claims, now that they know where to look," Feng said.
The team admits that their work is inconclusive and more experiments need to be conducted.
That doesn't stop the physicists speculating, however, and Feng said the new force could be joined to the electromagnetic, strong and weak nuclear force as "manifestations of one grander, more fundamental force."
Another theory proposes that the new force could be related to dark matter. There may be a separate dark sector complete with its own particles and forces that mirror those seen in the standard particle, Feng added.
"It's possible that these two sectors talk to each other and interact with one another through somewhat veiled but fundamental interactions," he said.
"This dark sector force may manifest itself as this protophobic force we're seeing as a result of the Hungarian experiment. In a broader sense, it fits in with our original research to understand the nature of dark matter." ®