DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

cosmic rays High energy subatomic particles.
Cosmic-ray primaries are mostly protons
and hydrogen nuclei, but they also contain heavier
nuclei. Their energies range from 1 to 2 billion
electron volts to perhaps 10 16 eV, though
the higher energies are rare. On colliding with
atmospheric particles, they produce many different
kinds of lower energy secondary cosmic
radiation. Many cosmic rays are produced in the
sun, but the highest-energy rays are produced
outside the solar system, perhaps in shocks associated
with supernova explosions.
cosmic spring Cosmic strings formed in the
early universe might have the ability to carry
currents. These currents were at some stage believed
to have the capability to locally remove
the string tension: the energy carried by the current
indeed tends to balance the string tension,
so that the effective tension could be made to
vanish, or even become negative, hence turning
a string into a spring (i.e., a tensionless string).
Detailed numerical investigations revealed that
the maximum allowed current was, in the case
of spacelike currents, not enough for this mechanism
to take place. The possibility that timelike
currents could make up springs is still open,
although quite unlikely, since reasonable equationsofstateshowthephasespacewhereitcould
happen to be very small.
Another possibility is that of static electromagnetically
supported string loops (some authors
adopt this as a definition of a spring). Here
it is not the current inertia that balances the string
tension, but the long-range electromagnetic field
generated by the current that would support the
whole configuration. In this particular case, the
string loop would be required to be unnaturally
large, due to the slow (logarithmic) growth of the
electromagnetic support around the string core.
Non-static but still stationary (rotating) configurations
are now believed to have a much more
important role to play in cosmology. See Carter–
Peter model, current saturation (cosmic string),
magnetic regime (cosmic string), tension (cosmic
string), vorton.
cosmic string A type of cosmic topological
defect that arises from symmetry breaking
schemes when the low temperature minimum of
the potential has a phase structure: φ =φ0e iϕ ,
© 2001 by CRC Press LLC
cosmic topological defect
where the ϕ is an arbitrary real phase, all values
of ϕ having the same (zero) energy. Then,
at large distances from the string, the phase can
continuously increase around the string, forcing
a high energy region along the line describing
the string.
Both local (which have an associated gauge
vector field that compensates much of the string
energy), and global (which have no such gauge
vector) strings may be formed depending on
whether the broken group is a gauge or a rigid
symmetry of the system before the transition, respectively.
See Abelian string, cosmic topological
defect, deficit angle (cosmic string), global
topological defect, homotopy group, local topological
defect.
cosmic texture Cosmic structures in which
multicomponent fields provide large scale matter
sources. Their dynamics can generate local
energy concentrations which act to seed subsequent
formation of structure (super cluster of
galaxies, etc.) in the universe. See cosmic topological
defect.
cosmic topological defect Current understanding
of the physics of the early universe
is based in part on the spontaneous breaking
of fundamental symmetries. These symmetry
breaking processes take place during phase transitions,
and many of these transitions might have
occurred at grand unified energy scales. At these
scales spacetime gets “oriented” by the presence
of a hypothetical field called generically the
“Higgs field”, pervading all the space. Different
models for the Higgs field lead to the formation
of a whole variety of topological defects with
very different characteristics and dimensions.
Some of the proposed theories have symmetry
breaking patterns leading to the formation of
“domain walls” (mirror reflection discrete symmetry):
incredibly thin (thickness comparable
to a Compton wavelength associated with particle
energy ∼ 10 15 GeV) planar surfaces, trapping
enormous concentrations of mass-energy,
which separate domains of conflicting field orientations,
similar to two-dimensional sheet-like
structures found in ferromagnets.
In other theories, cosmological fields are distributed
in such a way that the old (symmetric)
phase gets confined into a finite region