Improved treatment of cosmic microwave background fluctuations induced by a late-decaying massive neutrino - art. no. 123508

A massive neutrino which decays after recombination ((t greater than or equ al to 10(13) sec) into relativistic decay products produces an enhanced int egrated Sachs-Wolfe effect, allowing constraints to be placed on such neutr inos from present cosmic microwave background anisotropy data. Previous tre atments of this problem have approximated the decay products as an addition al component of the neutrino background. This approach violates energy-mome ntum conservation, and we show that it leads to serious errors for some neu trino masses and lifetimes. We redo this calculation more accurately, by co rrectly incorporating the spatial distribution of the decay products. For l ow neutrino masses and long lifetimes, we obtain a much smaller distortion in the CMB. fluctuation spectrum than have previous treatments. We combine these new results with a recent set of CMB data to exclude the mass and lif etime range m(h) > 100 eV, tau > 10(12) sec. Masses as low as 30 eV are exc luded for a narrower range in Lifetime. [S0556-2821(99)04824-9].