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Articles Cosmology Cosmological Constraints on Heavy Weakly Interacting Fermions (1981)
Cosmological Constraints on Heavy Weakly Interacting Fermions (1981) |
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(1) We assume throughout that all particles obey Maxwell-Boltzmann statistics, and have a single spin state.Ultrarelativistic boson (fermion) spin states would have number densities 
; we shall ignore the irrelevant corrections.
(2) We assume for now that the 
lifetime is much longer than the decoupling time.
(3) In general, the scale factor 
of a Friedmann universe varies according to 
. If 
, then 
, from eq. (2) is negligible for the large 
considered here.
(4) As discussed below, the temperature of the ambient gas may affect the decay rate of .
(5) In the relevant cases, the will be approximately at rest for most of their lifetime, so that time dilation effects are negligible.
(6) The decay of an could produce an average asymmetry of one unit of lepton number (but not baryon number (c.f., [8])).
