At the moment I am struggeling to find out about hidden sectors. So far I've been unable to find any in depth explicit discussion about them anywhere, so if someone here could answer some of my questions it would be very useful for me. On Wikipedia it mentions that hidden sector particles are particles that do not interact with matter via the usual gauge bosons W, Z, gluons and photons. However it does not really elaborate on this, so I'm left wondering what this really means. Are hidden sector particles essentially particles residing on some other dimesion? Any general explanation would be great. What type of particles exist in hidden sectors? Are there any limitations as to what particles are allowed to be hidden? I have heard an explanation concerning how we - in the ordinary sector - would observe the masses of hidden sector particles, but this invloved things like the distance of the particles from the intersection of extra-dimensional branes, which is waay over my head! So again any explanation about how we would, in theory, observe hidden sector masses (i.e. would they be large or small etc) would be good. Also, I'm interested in why people are interested in hidden sectors. Is it simply because they are invloved in extensions of the standard model, and so explore new physics? Any help would be much appreciated.