Experimental bounds on sterile neutrino mixing angles

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We derive bounds on the mixing between the left-chiral ("active") and the right-chiral ("sterile") neutrinos, provided from the combination of neutrino oscillation data and direct experimental searches for sterile neutrinos.

• We demonstrate that the mixing of sterile neutrinos with any flavour can be significantly suppressed, provided that the angle theta_13 is non-zero.
• This means that the lower bounds on sterile neutrino lifetime, coming from the negative results of direct experimental searches can be relaxed (by as much as the order of magnitude at some masses).
• We also demonstrate that the results of the negative searches of sterile neutrinos with PS191 and CHARM experiments are not applicable directly to the see-saw models.