==Neutrino questions== 
 Hi,  

 you indicated awhile ago that sterile neutrinos can oscillate with "normal" neutrinos.  I'm trying to understand sterile neutrinos.  I'm not clear whether "sterile" just means "right-handed".  Are they synonymous for neutrinos (with the usual proviso that we switch left/right for particle/anti-particle)?  If sterile neutrinos are just right handed neutrinos then it seems to me that they will have different weak hypercharge (0 for right-handed neutrinos, -1 for the left-handed neutrinos) and X charge.  If so, wouldn't that prevent their mixing?