Improved constraints on sterile neutrinos in the MeV to GeV mass range.

Improved upper bounds are presented on the coupling |Ue4|2 of an electron to a sterile neutrino ν4 from analyses of data on nuclear and particle decays, including superallowed nuclear beta decays, the ratios R(π)e/μ=BR(π+→e+νe)/BR(π+→μ+νμ), R(K)e/μ, R(Ds)e/τ, and B+e2 decay, covering the mass range from MeV to GeV. [ABSTRACT FROM AUTHOR]