In particle processes the forces are described as being due to the exchange of particles. For each type of force, there is an associated carrier particle.
The carrier particles include:
the photon - for electromagnetic force
the gluon - for strong force
(inside protons and neutrons)
the W and the Z particles - for the weak force
If there is a new force, there will be a new force-carrier particle. We hope to discover new forces through particles we call W' or Z'.