Hidden Valley Model (HVM) is a class of Hidden Sector Model (HSM) with strong dynamics and a spectrum light enough to be observed by the current collider experiments. Like the HSM, it proposes a hidden or dark sector that only communicates with the Stardard Model (SM) via some messenger field X. X is assumed to be heavy or couples very weakly to the SM, which could explain why it is difficult to observe. These models hypothesize the existence of particles, other than the known Standard Model Particles, which interacts very weakly.
These models can explain the excess in cosmic ray mon events with high muon multiplicities that has been reported from cosmic ray studies with ALEPH and DELPHI detectors. It can also partially account for the excess in multi-muon events that was found by the CDF experiment.