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

Improved upper bounds are presented on the coupling vertical bar U-e4 vertical bar(2) of an electron to a sterile neutrino nu(4) from analyses of data on nuclear and particle decays, including superallowed nuclear beta decays, the ratios R-e/mu((pi)) = BR(pi(+) -> e(+)nu(e))/BR(pi(+) -> mu(+)nu(mu)) R-e/mu((K)), R-e/tau((Ds)) and B-e2(+) decay, covering the mass range from MeV to GeV.