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    Original URL path: /~whu/polar/polar.html (2015-06-26)





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    Original URL path: /~whu/acoustic/acoustic.html (2015-06-26)


  • CMB Intermediate
    Acoustic Oscillations Baryonmeter Doppler Effect Driving Effect Damping Projection ISW Effect Power Spectrum Sensitivity Secondary Anisotropy Summary Reionization We know that the universe has been ionized at least until z 5 from the null detection of the Gunn Peterson effect Hence after standard recombination at z 1000 the universe must have underwent reionization However the amount of rescattering of CMB photons is negligible unless the ionization persists through redshifts of several tens This is unlikely in models without excessive small scale power and in such models e g scale invariant adiabatic ones degree scale anisotropy detections are already severely constraining the amount of reionization allowable Still it is useful to recall the basic physical effects associated with reionization Figure Reionization Effects from Hu White 1995 Rescattering Damping Rescattering damps fluctuations in the same manner as diffusion Scattering eliminates anisotropies leaving them only in the unscattered fraction exp optical depth Since outside the horizon streaming has not yet converted temperature fluctuations to anisotropies power is only lost below the horizon at the rescattering epoch Doppler Effect Diffusion and rescattering prevents the appearance of large temperature fluctuations However the Doppler effect from scattering off electrons caught in the gravitational instability of the baryons can regenerate anisotropies These contributions are suppressed in the same way as the late ISW effect Figure Cancelled Doppler Effect from Hu 1995 Photons that last scattered off opposite sides of the perturbation get Doppler shifted by equal and opposite amounts Thus for wavelengths far below the thickness of the last scattering surface Doppler contributions tend to cancel leaving a negligible net effect Non linear Effects At very small scales higher order contributions are more efficient than the Doppler effect in regenerating anisotropies These generally make use of combining the Doppler effect with variations in the optical depth For

    Original URL path: http://background.uchicago.edu/~whu/physics/aux/secondary.html (2015-06-26)
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  • Gravitational Lensing
    out sharp features in the spectrum of primary anisotropies The amount of lensing is highly dependent on the model In the popular scale invariant adiabatic model it is unlikely to make features such as the acoustic peaks unobservable see Seljak

    Original URL path: http://background.uchicago.edu/~whu/physics/aux/lensing.html (2015-06-26)
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  • CMB Introduction
    scattering and at full matter domination can have strongly enhanced anisotropy contributions from this effect These join smoothly onto driven acoustic contributions and form a potential envelope for the anisotropies Late ISW Effect In an open or lambda model the universe enters a rapid expansion phase once matter no longer dominates the expansion As density fluctuations are frozen in the potential again decays leading to an ISW effect Opposing effects from decaying overdensities and underdensities tend to cancel if the photons can travel across many wavelengths during the decay Figure Late ISW Cancellation as is the case for fluctuations under the horizon size at the end of matter domination This scale is projected onto a large angle in the anisotropy spectrum both because of the intrinsically large size of the horizon at such late epochs and because the point of origin of the effect is much closer than the last scattering surface This makes the same physical scale subtend a much larger angular scale Figure Angular vs Physical Scale from Hu Sugiyama 1995b Contributions to the anisotropy in a Lambda model as a function of both angle multipole l and physical scale wavenumber k The projection takes secondary contributions such as ISW effects from the same physical scale to a larger angular scale than the primary Sachs Wolfe SW effect The ridgelike structure of the contributions comes from the projection of plane waves onto the sphere Bessel function oscillations The observable angular power spectrum comes from integrating in k the anisotropy contributions for each multipole see Hu White 1995 especially this figure For a fixed matter density matter domination ends sooner in an open than a lambda universe Thus the angular scale of the cancellation cut off in the spectrum is larger in a lambda universe Rees Sciama Effect Once

    Original URL path: http://background.uchicago.edu/~whu/physics/aux/isw.html (2015-06-26)
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    Original URL path: /~whu/cmbex.html (2015-06-26)




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    Original URL path: /~whu/concepts/concepts.html (2015-06-26)


  • PowerPoint Presentation - Extragalactic Foreground SourcesÉand You!

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    Original URL path: /~whu/Courses/Ast280/Ben/Astro_files/frame.htm (2015-06-26)




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