A question for the panel:
The "dark sector" represents particles that interact with standard model particles only via gravity. I'm sure I've seen suggestions for an "even darker" sector that doesn't even interact via gravity. So effectively it is completely non-interacting with any particles we know of (though it still interacts with itself). However I've forgotten what the catchy name for this sector was.
Has anyone else come across this idea and if so can you remember what name it was given?