Analysis of techni-dilaton as a dark matter candidate
  The almost conformal dynamics of walking technicolor (TC) implies the
existence of the approximate scale invariance, which breaks down spontaneously
by the condensation of anti-techni and techni-fermions. According to the
Goldstone theorem, a spinless, parity-even particle, called techni-dilaton
(TD), then emerges at low energy. If TC exhibits an extreme walking, TD mass is
parametrically much smaller than that of techni-fermions (around 1 TeV), while
its decay constant is comparable to the cutoff scale of walking TC. We analyze
the light, decoupled TD as a dark matter candidate and study cosmological
productions of TD, both thermal and non-thermal, in the early Universe. The
thermal population is governed dominantly by single TD production processes
involving vertices breaking the scale symmetry, while the non-thermal
population is by the vacuum misalignment and is accumulated via harmonic and
coherent oscillations of misaligned classical TD fields. The non-thermal
population turns out to be dominant and large enough to explain the abundance
of presently observed dark matter, while the thermal population is highly
suppressed due to the large TD decay constant. Several cosmological and
astrophysical limits on the light, decoupled TD are examined to find that the
TD mass is constrained to be in a range between 0.01 eV and 500 eV. From the
combined constraints on cosmological productions and astrophysical
observations, we find that the light, decoupled TD can be a good dark matter
candidate with the mass around a few hundreds of eV for typical models of
(extreme) walking TC. We finally mention possible designated experiments to
detect the TD dark matter.
