Actually the mediator particle with the electroweak (or the electromagnetic and the weak forces) is the photon. Photons are what makes up light, radio, uv, infrared, etc waves. While it has not been proven that photons have mass, think about this... The less mass something has the less effect gravity (i.e. another mass) has on it right? Well, light is warped by large masses (stars and galaxies for example)and is trapped by black holes. If you see gravity as the warping and bending of space-time, light follows the bends and curves of space-tome. This means that light has mass. If light had no mass, it could not be the mediator particle with the electroweak force and it could not interact with particles affected by gravity. If I have anything mixed up ehre, someone please let me know. Otherwise, I hope I`ve helped you out. I think I confused myself actually ;)
Bladesinger