Tachyons
In special relativity, it is impossible to accelerate an object to the speed of light, or for a massive object to move at the speed of light. However, it might be possible for an object to exist which always moves faster than light. The hypothetical elementary particles with this property are called tachyonic particles. Attempts to quantize them failed to produce faster-than-light particles, and instead illustrated that their presence leads to an instability.
Various theorists have suggested that the neutrino might have a tachyonic nature, while others have disputed the possibility.
Read more about this topic: Faster-than-light