Fifth Force...

Credit: Avariel Falcon/Flickr, CC BY 2.0

Topics: Experimental Physics, Particle Physics, Radiation, Theoretical Physics

The Four (currently well-known) Forces: The Strong Force, the Electromagnetic Force, the Weak Force and Gravity. See: this link, which includes a brief primer on each and Feynman Diagrams on the strong and weak forces. Debate is going on now whether the new Force is evidence of Dark Energy, Dark Matter; a "Dark Photon" at 17 MeV, or what they refer to in the article as a "protophobic X (Greek letter Chi) boson." As with all reporting of scientific investigations, this is in its preliminary stages.

A laboratory experiment in Hungary has spotted an anomaly in radioactive decay that could be the signature of a previously unknown fifth fundamental force of nature, physicists say—if the finding holds up.

Attila Krasznahorkay at the Hungarian Academy of Sciences’s Institute for Nuclear Research in Debrecen, Hungary, and his colleagues reported their surprising result in 2015 on the arXiv preprint server, and this January in the journal Physical Review Letters. But the report – which posited the existence of a new, light boson only 34 times heavier than the electron—was largely overlooked.

Then, on April 25, a group of US theoretical physicists brought the finding to wider attention by publishing its own analysis of the result on arXiv. The theorists showed that the data didn’t conflict with any previous experiments—and concluded that it could be evidence for a fifth fundamental force. “We brought it out from relative obscurity,” says Jonathan Feng, at the University of California, Irvine, the lead author of the arXiv report.

Four days later, two of Feng's colleagues discussed the finding at a workshop at the SLAC National Accelerator Laboratory in Menlo Park, California. Researchers there were sceptical but excited about the idea, says Bogdan Wojtsekhowski, a physicist at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. “Many participants in the workshop are thinking about different ways to check it,” he says. Groups in Europe and the United States say that they should be able to confirm or rebut the Hungarian experimental results within about a year.

Scientific American:
Some theorists say a radioactive decay anomaly could imply a fundamental new force
Edwin Cartlidge