In astronomy and cosmology, light dark matter
are dark matter weakly interacting massive
particles (WIMPS) candidates with masses less
than 1 GeV.
These particles are heavier than warm dark
matter and hot dark matter, but are lighter
than the traditional forms of cold dark matter.
The Lee-Weinberg bound limits the mass of
the favored dark matter candidate, WIMPs,
that interact via the weak interaction to
≈
2
{\displaystyle \approx 2}
GeV.
This bound arises as follows.
The lower the mass of WIMPs is, the lower
the annihilation cross section, which is of
the order
≈
m
2
/
M
4
{\displaystyle \approx m^{2}/M^{4}}
, where m is the WIMP mass and M the mass
of the Z-boson.
This means that low mass WIMPs, which would
be abundantly produced in the early universe,
freeze out (i.e. stop interacting) much earlier
and thus at a higher temperature, than higher
mass WIMPs.
This leads to a higher relic WIMP density.
If the mass is lower than
∼
2
{\displaystyle \sim 2}
GeV the WIMP relic density would overclose
the universe.
Some of the few loopholes allowing one to
avoid the Lee-Weinberg bound without introducing
new forces below the electroweak scale have
been ruled out by accelerator experiments
(i.e.
CERN, Tevatron), and in decays of B mesons.A
viable way of building light dark matter models
is thus by postulating new light bosons.
This increases the annihilation cross section
and reduces the coupling of dark matter particles
to the Standard Model making them consistent
with accelerator experiments.
== Motivation ==
In recent years, light dark matter has become
popular due in part to the many benefits of
the theory.
Sub-GeV dark matter has been used to explain
the positron excess in the galactic center
observed by INTEGRAL, excess gamma rays from
the galactic center and extragalactic sources.
It has also been suggested that light dark
matter may explain a small discrepancy in
the measured value of the fine structure constant
in different experiments.
== See also ==
Axion
Axion Dark Matter Experiment
Dark matter halo
Minimal Supersymmetric Standard Model
Neutralino
Scalar field dark matter
Weakly interacting massive particles
