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Paper   IPM / Physic / 15828
School of Physics
  Title:   Ultra-light scalar saving the 3+1 neutrino scheme from the cosmological bounds
  Author(s):  Y. Farzan
  Status:   Published
  Journal: Phys. Lett. B
  Vol.:  797
  Year:  2019
  Pages:   134911
  Supported by:  IPM
The LSND and MiniBooNE results as well as the reactor and Gallium anomalies seem to indicate the presence of a sterile neutrino with a mass of  ∼ 1 eV mixed with active neutrinos. Such sterile neutrino can be produced in the early universe before the neutrino decoupling, leading to a contribution to the effective number of neutrinos (Neff) as well as to a contribution to the sum of neutrino masses which are in tension with cosmological observations. We propose a scenario to relax this tension by a Yukawa coupling of the sterile neutrinos to ultra-light scalar particles which contribute to the dark matter in the background. The coupling induces an effective mass for νs which prevents its production in the early universe. We discuss the implications for the upcoming KATRIN experiment and future relic neutrino search experiments such as PTOLEMY. We also briefly comment on certain non-renormalizable forms of interaction between νs and the scalar and their consequences for the νs production in the early universe.

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