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As I understand it, there are lots of current theories of dark matter and
dark energy, with probably most interest being paid to dark energy at this
time. I think the general consensus on dark matter is that it's comprised
of some as of yet undescivored weakly interacting particle (these
particles can remain quite massive without decaying if they decouple from
the rest of the stuff in the universe while they are non-relativistic-
these candidates are called 'cold dark matter'). The most popular such
candidate would be the lightest supersymmetric particle (or LSP). Another
candidate that I believe is still fashionable to talk about is the axion.
The axion would not constitute new physics per se, although it remains to
be discovered, it's origin in particle physics is consistent with the
standard model. And, well, supersymmetry is supersymmetry.
As for dark energy, there are lots of theories- cosmological constant,
quintessence, Chaplygen gas, X-matter, variations thereof and others. The
basic idea is that the dark energy component has the same properties as
the vacuum energy of a scalar field- negative pressure. The exact source
of this vacuum energy and its behavior is what sets the above ideas apart.
These vary from inflation-type scalar fields slowly evolving in their
potentials, exotic matter with a weird equation of state, time-varying
cosmological 'constant' etc etc etc. It's a real zoo. As you can see,
some of these require new physics, others, such as a relic scalar field
with non-vanishing vacuum energy fit well into the standard model
(although, no fundamental scalars have been seen yet!!)
Lastly, as for the baryonic matter, this includes everything from the
standard model- leptons, quarks, gauge fields. One of the more confusing
misnomers out there....
Brian Powell
SUNY Buffalo
On Tue, 4 Jan 2005, Daniel Crowe wrote:
From my limited understanding of dark matter and dark energy, it seemsthat new physics is needed to explain them. The development of this new
physics might have an impact on physics similar to the impact of the
development of quantum mechanics and relativity during the early twentieth
century.
According to Freedman and Turner, only 4% of the mass-energy density of
the universe is due to baryonic matter, 23% is due to dark matter, and 73%
is due to dark energy. They state that some of the dark matter (0.1% to
5% of the total density of the universe) must be due to neutrinos.
Can anyone shed any light on the current status of the theories of dark
matter and dark energy, and whether new physics is necessary to explain
them? Also, does baryonic matter include mesons and charged leptons, or
are their contributions negligible anyway?
Daniel Crowe
Oklahoma School of Science and Mathematics
Ardmore Regional Center
dcrowe@sotc.org
Reference:
Freedman, Wendy L. & Michael S. Turner (October 2003) "Cosmology in the
New Millenium" Sky & Telescope 106(4)30-41.
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