Speaker
Dr
Tomohiro Nakama
(Johns Hopkins University)
Description
The small-scale crisis, discrepancies between observations and
N-body simulations, may imply suppressed matter
fluctuations on subgalactic distance scales. Such a suppression
could be caused by some early-universe mechanism (e.g., broken
scale-invariance during inflation), leading to
a modification of the primordial power spectrum at the onset of
the radiation-domination era. Alternatively,
it may be due to nontrivial dark-matter properties (e.g., new
dark-matter interactions or warm dark matter) that affect the matter
power spectrum at late times, during radiation domination, after
the perturbations re-enter
the horizon. We show that early- and late-time suppression
mechanisms can be distinguished by measurement of the $\mu$
distortion to the frequency spectrum of the cosmic microwave
background. This is because the $\mu$ distortion is
suppressed, if the power suppression is primordial, relative to
the value expected from the dissipation of standard
nearly-scale-invariant fluctuations. We emphasize that the
standard prediction of the $\mu$ distortion remains unchanged
in late-time scenarios even if the dark-matter effects occur
before or during the era (redshifts $5\times 10^4 \lesssim z
\lesssim 2\times 10^6$) at which $\mu$ distortions are
generated.
Primary author
Dr
Tomohiro Nakama
(Johns Hopkins University)