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waynehu

Professor, Department of Astronomy and Astrophysics
University of Chicago

Group Contact CV SnapShots
CMB Introduction '96   Intermediate '01   Polarization Intro '01   Cosmic Symphony '04   Polarization Primer '97   Review '02   Power Animations   Lensing   Power Prehistory   Legacy Material '96   PhD Thesis '95 Baryon Acoustic Oscillations Cosmic Shear Clusters
Transfer Function WMAP Likelihood Reionization PPF for CAMB Halo Mass Conversion Cluster Abundance
Cosmology I [legacy 321] Cosmology II [321] Current Topics [282] Galaxies and Universe [242] Radiative Processes [305] Research Preparation [307] GR Perturbation Theory [408] CMB [448] Cosmic Acceleration [449]

Peak Suppression

Like scattering before recombination, scattering at late times suppresses anisotropies in the distribution that have already formed. Reionization therefore suppresses the amplitude of the acoustic peaks by the fraction of photons rescattered, approximately the optical depth $\sim \tau_{{\rm ri}}$ (see Plate 5b, dotted line and negative, dashed line, contributions corresponding to $\vert\delta \Delta_T^2\vert^{1/2}$ between the $z_{\rm ri}=7$ and $z_{\rm ri}=0$ models). Unlike the plasma before recombination, the medium is optically thin and so the mean free path and diffusion length of the photons is of order the horizon itself. New acoustic oscillations cannot form. On scales approaching the horizon at reionization, inhomogeneities have yet to be converted into anisotropies (see §3.8) and so large angle fluctuations are not suppressed. While these effects are relatively large compared with the expected precision of future experiments, they mimic a change in the overall normalization of fluctuations except at the lowest, cosmic variance limited, multipoles.


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