ultrarelativistic
Adjective
Meaning
ultrarelativistic
(physics) Moving at a speed very close to the speed of light.
Examples
This does not significantly affect the experiments, because neutrinos involved are nearly always ultrarelativistic, and thus mixing amplitudes are vanishingly small.
On February 28, 2013, a third radiation belt, consisting of high-energy ultrarelativistic charged particles, was reported to be discovered.