singlet = ?

Context:


Illustration of singlet time travel theory. When a pair of protons collide in the Large Hadron Collider, the resultant explosion may create a special type of particle, called a Higgs singlet, that is capable of traveling forward and back in time. It would do so by leaving familiar three-dimensional space to travel in an extra dimension. (Credit: Jenni Ohnstad / Vanderbilt)

More:

http://www.sciencedaily.com/releases/2011/03/110315163330.htm