Do all massless particles travel at the speed of light?

[RAD4921]

I know photons have no mass but are there other particles that have no mass and if so can they travel at the speed of light?
Thanks RAD

 

[mathman]

Gravitons (yet to be discovered?) and gluons (strong nuclear force carrier) have no mass. Gravitons travel at the speed of light. Gluons (in ordinary circumstances) exist inside nuclei, so they don't travel much.

 

[rbj]

and, if they travel at speed, c, they got to have no rest mass (which is what we mean by "massless"). photons actually do have mass, namely:

$$m = \frac{E}{c^2} = \frac{h \nu}{c^2}$$

just no "rest mass" a.k.a. "invariant mass".