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Fermi National Accelerator Laboratory

Summary: Fermi National
Accelerator Laboratory
NASA/Fermilab Astrophysics Center
Telling Three from Four Neutrinos
with Cosmology
Kevork N. Abazajian
NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory,
Batavia, Illinois 60510-0500, USA
New results, namely the independent determination of the deuterium abundance
in several quasar absorption systems, and the complementary determination of the
cosmological baryon density by observations of anisotropies in the cosmic microwave
background (CMB), allow for a reevaluation of the constraints on the relativistic
particle content of the universe at primordial nucleosynthesis. Expressed in terms
of the neutrino energy density, we nd 1:7 < N  < 3:5 (95% CL). In particu-
lar, we show that phenomenological four neutrino models including a sterile state
(not participating in SU(2)L U(1) Y interactions) unavoidably thermalize a fourth
neutrino, and are highly disfavored in the standard minimal model of primordial


Source: Abazajian, Kev - Theoretical Astrophysics, Fermilab


Collections: Physics