Stars as Laboratories for Fundamental Physics - MPP Theory Group

Radiative Particle Decays 489
Fig. 12.20. Cosmological limits on neutrino radiative lifetimes according to
Kolb and Turner (1990). The radiative mode is assumed to be the only decay
channel. The shaded area is excluded according to Sect. 7.1.5 (Fig. 7.2).
rate at nucleosynthesis. These limits (shaded area in Fig. 12.20) are
more general because they do not depend on the nature of the final
states in the decay.
Kolb and Turner’s (1990) exclusion plot is somewhat schematic.
Ressell and Turner (1990) performed a much more detailed analysis on
the basis of the diffuse photon backgrounds in all wavebands. Probably
the most interesting region is that of small neutrino masses and large
lifetimes (the upper left corner of Fig. 12.20). The excluded range of
effective electromagnetic transition moments for m ν < 30 eV is shown
in Fig. 12.21. It may be useful to approximate the excluded range
analytically by
µ eff ∼ < 3×10 −11 µ B (eV/m ν ) 2.3 (12.38)
which is shown as a dashed line in Fig. 12.21.
Using favored cosmological parameters (Ωh 2 ≈ 0.3) neutrinos with
m ν ≈ 30 eV would be the dark matter of the universe. With smaller
masses there would have to be another component, but neutrinos could