Impressions of the WMAP Results

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Impressions of the WMAP Results
Scott Dodelson EFI Symposium February 14, 2003
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Acoustic Peaks
Displacement of a string
Temperature perturbation
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Musical Acoustics

• Middle C
• Middle C on a piano

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Technical problems How does string vibration
affect air? How do air vibrationsaffect ear?
How do perturbations in temperature at LSS show
up asanisotropies today?
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Fourier transformof temperature atLast
Scattering Surface
Anisotropy spectrum today
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Why peaks and troughs?

• Vibrating String Characteristic frequencies
  because ends are tied down
• Temperature in the Universe Small scale modes
  enter the horizon earlier than large scale modes

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But, the universe is different than a violin
string
There are many, many modes with similar values of
k. All have different initial amplitude. But all
are in phase.
First Peak
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An infinite number of violins are synchronized
Similarly, all modes corresponding to first
trough are in phase they all have zero amplitude
at recombination
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Without coherence
First Trough
First Peak
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When we see this, we conclude that modes were set
in phase during inflation!
Bennett et al. 2003
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Three Step argument for ltTEgt

• Polarization proportional to quadrupole
• Quadrupole proportional to dipole
• Dipole out of phase with monopole

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Isotropic radiation field produces no
polarization after Compton scattering
Modern Cosmology February 21, 2003 Adapted from
Hu White 1997
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• Radiation with a dipole produces no polarization

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• A quadrupole is needed

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Quadrupole proportional to dipole
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• Dipole is out of phase with monopole

Roughly,
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The product of monopole and dipole is initially
positive (but small, since dipole vanishes as k
goes to zero) and then switches signs several
times.
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DASI initially detected TE signal
Kovac et al. 2002
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WMAP has indisputable evidence that monopole and
dipole are out of phase
Kogut et al. 2003
This is most remarkable for scales around l100,
which were not in causal contact at
recombination.
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WMAP gets a better fit with spectral index n not
constant A running spectrum
The Age of sifting through inflationary models
has begun
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Expand the spectral index about a pivot point
If this is of order e, then this is typically
of order e2 where e is some small number.
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Not many slow roll models have running this large
with n-1 this small.
n
Peiris et al. 2003
n
Perhaps this is points to particular class of
models
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But models which have n comparable to n
typically have n of the same order

• Terms must be re-summed (Stewart 2002 Dodelson
  Stewart 2002)
• The resulting spectrum will generally not be
  characterized by tilt running.

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Wisecrack example n-n
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Morals

• Only a model allows extrapolation past the data
  (k1 Mpc-1 ).
• Its not clear whether there are many models with
  large running that can be described only by
  running.
• We need new innovative ways of sorting through
  inflationary models (Hoffman Turner 2001,
  Kinney 2002, Peiris et al. 2003)

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Other Random Thoughts

• Is c2 really that bad? Is noise known to better
  than 3.5? In cosmic variance limited region,
  noise is proportional to signal?
• It will be fascinating to see cross-correlations
  with other experiments. This must be done to
  combine different data sets.

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Conclusions

• Wow!

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Parameters I

• Reionization lowers the signal on small scales
• A tilted primordial spectrum (nlt1) increasingly
  reduces signal on small scales
• Tensors reduce the scalar normalization, and thus
  the small scale signal

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Parameters II

• Baryons accentuate odd/even peak disparity
• Less matter implies changing potentials, greater
  driving force, higher peak amplitudes
• Cosmological constant changes the distance to LSS