### Max Tegmark's cosmology library: openreion

Please click here to download the paper
described below.
Since this postscript file does not include the figures, I strongly
suggest that you download my
Ph.D. thesis
instead, in which this paper constitutes Chapter 4.
Click
here
if you are interested in
other research of mine.

##
REIONIZATION IN AN OPEN CDM UNIVERSE:

IMPLICATIONS FOR COSMIC MICROWAVE BACKGROUND FLUCTUATIONS

### Authors:

Max Tegmark & Joe Silk
### Abstract:

We generalize
previous work
on early photoionization
to CDM models with Omega<1.
Such models have received recent interest because
the excess power in the large-scale galaxy distribution
is phenomenologically fit if the ``shape parameter"
Gamma=h Omega_0 is about 0.25.
It has been argued that such models may require early
reionization to suppress small-scale anisotropies
in order to be consistent with experimental data.
We find
that if
the cosmological constant lambda=0, the extent of this suppression is
quite insensitive to Omega_0.
Given a sigma_8-normalization today,
the loss of small-scale power associated
with a lower Omega_0 is partially canceled by higher optical depth from
longer lookback times and by structures forming at higher
redshifts before
the universe becomes curvature-dominated.
The maximum angular scale on which fluctuations are
suppressed decreases when Omega_0 is lowered,
but this effect is also rather weak and unlikely to be
measurable in the near future.
For flat models, on the other hand, where
lambda_0 = 1-Omega_0, the negative effects of lowering Omega_0
dominate, and early reionization is not likely to play a
significant role if Omega_0<<1. The same applies to
CDM models
where the effective Gamma is lowered by increasing the number of
relativistic particle species.

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This page was last modified July 1, 1998.
max@ias.edu