In a new paper published in Physical Review Letters, physicists Yu-Sheng Liu, David McKeen, and Gerald A. Miller at the University of Washington
in Seattle have hypothesized the existence of a new particle that looks very enticing because it could simultaneously solve two important problems:
the proton radius puzzle and a discrepancy in muon anomalous magnetic moment measurements that differ significantly from standard model predictions.
Hypothetical new particle could solve two major problems in particle physics
http://phys.org/news/2016-09-hypothetical-particle-major-problems-physics.html