Chapter 6
Supersymmetric dark matter
6.1 Introduction
The cosmological bounds on the masses of various known or hypothethical relic
particles derive from the requirement that the total energy density of the relic
particles X does not exceed the measured present total energy density po. In
terms of dimension less quantities, this gives
nx.o < no
(6.1)
where nx.o and no are defined in (5.16) and (1.41) with no given by (5.19).
Some of the relics are known. For example, the present photon energy density
Pr = ~ T04, with To = 2.73 K = 2.35 x 10-4 e V the present temperature of the
cosmic microwave background, gives ny h 2 ::::: 2.471 x lO- s . Thus,
ny = 5.1 x lO- s
(6.2)
taking h = 0.71~:g; as in (5.14). Similarly, and as noted previously, the
measured primordial deuterium and helium abundances require that the baryon
energy density gives nbh2 = 0.019 ± 0.003. Thus,
nb = 0.039 ± 0.004
(6.3)
and baryons constitute not more than a few percent of the total. Relic neutrinos
also contribute and we may invert (5.35) to obtain a contribution of
m"
n"ji =
(6.4)
47.4eV
for each relativistic species with m" » To. The current experimental bound for
the electronic species from the Mainz and Troitsk tritium beta-decay experiment
[ 1) is far more restrictive:
m,,~ < 2.2eV
at 95% CL.
(6.5)
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DOl: 10.1201/9780367806637-6