Well, the class of theories already alluded to and known as supersymmetry theories require that as-yet undiscovered particles ought to exist.

Another is that the proton-antiproton collisions sometimes create some as yet undiscovered particle similar to those that carry the "weak" nuclear force.

For more than a decade, the leading theory envisaged a universe full of slow-moving exotic particles, as yet undiscovered, known as cold dark matter.

Feinberg also suggested that telepathy may exist due to as yet undiscovered elementary particles which he called 'psychons' or 'mindons'.

Other undiscovered particles could also be knocking around in the nucleus and helping the decay take place, Dr. Klapdor-Kleingrothaus said.

The agent for this "spontaneous symmetry breaking" was a particle, still undiscovered, called the Higgs.

The difference, called an anomaly by physicists, means the universe must contain previously undiscovered particles.

His theory include a "observerse", a 14-dimensional space, and predictions for undiscovered particles which could account for dark matter.

One example of this is how there are many theories that predict undiscovered particles.

Until recently, most scientists favored the idea of cold dark matter, exotic and as yet undiscovered particles that are weakly interacting, hence cold.