Sterile neutrinos in tau lepton decays

We study possible contributions of heavy sterile neutrinos nu (h) to the decays tau (-) --> e(+/-)(mu (+/-))pi (-/+)pi (-). From the experimental upper bounds on their rates we derive new constraints on the nu (h)-nu (tau) mixing in the mass region 140.5 MeV less than or equal to m(nuh) less than or equal to 1637 MeV. We discuss cosmological and astrophysical status of nu (h) in this mass region and compare our constraints with those recently derived by the NOMAD Collaboration. (C) 2001 Elsevier Science B.V. All tights reserved.