Colloquium March 6th, 2014 -- Axion Dark Matter
Δημοσιεύτηκε στις 6 Μαρ 2014
Pierre Sikivie
University of Florida
Axion Dark Matter
The
axion is a hypothetical particle originally postulated to explain why
the strong interactions are parity invariant. It is also one of the
leading candidates for the dark matter of the universe. I'll briefly
review the limits on the axion from particle physics, stellar evolution
and cosmology. The various constraints suggest that the axion mass is in
the micro-eV to milli-eV range. In this window, axions contribute
significantly to the energy density of the universe in the form of cold
dark matter. It was recently found that dark matter axions thermalize
and form a Bose-Einstein condensate (BEC). As a result, it may be
possible to distinguish axions from other forms of dark matter, such as
weakly interacting massive particles (WIMPs), on observational grounds.
Axions accreting onto a galactic halo fall in with net overall rotation
because almost all go to their lowest energy available state for given
angular momentum. In contrast, WIMPs accrete onto galactic halos with an
irrotational velocity field. The inner caustics are different in the
two cases. I'll argue that at least part of the dark matter is axions
because there is observational evidence for the type of inner caustic
produced by, and only by, an axion BEC.
University of Florida
Axion Dark Matter
The
axion is a hypothetical particle originally postulated to explain why
the strong interactions are parity invariant. It is also one of the
leading candidates for the dark matter of the universe. I'll briefly
review the limits on the axion from particle physics, stellar evolution
and cosmology. The various constraints suggest that the axion mass is in
the micro-eV to milli-eV range. In this window, axions contribute
significantly to the energy density of the universe in the form of cold
dark matter. It was recently found that dark matter axions thermalize
and form a Bose-Einstein condensate (BEC). As a result, it may be
possible to distinguish axions from other forms of dark matter, such as
weakly interacting massive particles (WIMPs), on observational grounds.
Axions accreting onto a galactic halo fall in with net overall rotation
because almost all go to their lowest energy available state for given
angular momentum. In contrast, WIMPs accrete onto galactic halos with an
irrotational velocity field. The inner caustics are different in the
two cases. I'll argue that at least part of the dark matter is axions
because there is observational evidence for the type of inner caustic
produced by, and only by, an axion BEC.
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