phys.org: "If true, it's revolutionary," said Jonathan Feng, professor of physics [and] astronomy. "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." via University of California, Irvine
'The UCI researchers came upon a mid-2015 study by experimental nuclear physicists at the Hungarian Academy of Sciences who were searching for "dark photons," particles that would signify unseen dark matter, which physicists say makes up about 85 percent of the universe's mass. The Hungarians' work uncovered a radioactive decay anomaly that points to the existence of a light particle just 30 times heavier than an electron.
'"The experimentalists weren't able to claim that it was a new force," Feng said. "They simply saw an excess of events that indicated a new particle, but it was not clear to them whether it was a matter particle or a force-carrying particle."
'The UCI group studied the Hungarian researchers' data as well as all other previous experiments in this area and showed that the evidence strongly disfavors both matter particles and dark photons. They proposed a new theory, however, that synthesizes all existing data and determined that the discovery could indicate a fifth fundamental force.'
"Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays" by Jonathan L. Feng, et al here