Seminars IFIC

# Ultra-light scalar saving the 3+1 neutrino scheme from the cosmological bounds

## by Yasaman Farzan (IPM, Tehran & ICTP, Trieste)

4-4-4426 - Seminari Física Teòrica (Campus Burjassot)

### 4-4-4426 - Seminari Física Teòrica

#### Campus Burjassot

20
Description
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 the sterile neutrino 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.

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