Stars as Laboratories for Fundamental Physics - MPP Theory Group

22 Chapter 1
can be compensated by a strong coupling. For particles with a different
interaction structure the equivalent of Fig. 1.1 would look qualitatively
similar, albeit different in detail.
Particles are not harmless in stars just because they are trapped,
or just because their mass exceeds a typical temperature. However, in
practice new particles are usually thought to be very weakly interacting
and either essentially massless on the scales of stellar temperatures, or
else very massive on those scales. In this book I will focus on low-mass
particles with very weak interactions so that the energy-loss argument
will be in the foreground of the discussion.
The opposite case of weakly interacting massive particles (WIMPs)
is of great interest in the framework of a hypothesis which holds that
such objects are the dark matter of the universe. (Another dark matter
candidate are axions which fall into the low-mass category covered in
this book.) WIMP masses would be in the 10 GeV range and above so
that they cannot be produced in stars, but they can be captured from
the galactic background. They would contribute to the energy transfer
by conduction. Hence their role in stars is similar to that of electrons,
except for their large mfp which allows them to contribute significantly
even if their concentration is low. I do not treat this subject because
it requires entirely different formal tools from those relevant for lowmass
particles. The fascinating story of WIMPs in stars will be told
comprehensively within a forthcoming review paper Supersymmetric
Dark Matter by Jungman, Kamionkowski, and Griest (1995).