Is cosmology compatible with sterile neutrinos?

Area of Science:

• Cosmology
• Particle Physics
• Astrophysics

Background:

• Neutrinos are fundamental particles with mass, but the existence and properties of a potential fourth sterile neutrino remain uncertain.
• The Liquid Scintillator Neutrino Detector (LSND) anomaly suggests new neutrino physics beyond the Standard Model.
• Cosmic Microwave Background (CMB), large-scale structure (LSS), and Lyman-alpha forest observations provide crucial cosmological data.

Purpose of the Study:

• To constrain the mass and cosmological abundance of a hypothetical fourth, sterile neutrino.
• To test the sterile neutrino hypothesis as an explanation for the LSND anomaly.
• To explore the implications of active neutrino masses and non-thermal sterile neutrino abundances.

Main Methods:

• Combined data from WMAP (third year results), LSS surveys, and Lyman-alpha forest observations.
• Performed statistical analysis to derive constraints on sterile neutrino mass (ms) and energy density (omeganu).
• Generalized the analysis to include active neutrino masses and non-thermal sterile neutrino distributions.

Main Results:

• Constrained the sterile neutrino mass to ms < 0.26 eV (95% C.L.) and ms < 0.44 eV (99.9% C.L.).
• High-significance exclusion of the sterile neutrino hypothesis as the cause of the LSND anomaly.
• For non-thermal sterile neutrinos, omeganu < 0.003 (95% C.L.) for masses >1 eV or <0.05 eV, but up to 0.01 for ms ~ 0.25 eV.

Conclusions:

• The combined cosmological data strongly disfavors a sterile neutrino as the explanation for the LSND anomaly.
• The mass and abundance constraints are significant for models of neutrino physics and early universe cosmology.
• Further investigation into non-thermal sterile neutrino scenarios is warranted for specific mass ranges.