# Presentation: 073752

## Impressions of the WMAP Results

- Scott Dodelson
- EFI Symposium
- February 14, 2003

## “Acoustic” Peaks

- Displacement of a string

- Temperature perturbation

## Musical Acoustics

- Middle C
- Middle C on a piano

- Technical problems: How does string vibration affect air? How do air vibrationsaffect ear? ... How do perturbations in temperature at LSS show up asanisotropies today?

- Fourier transformof temperature atLast Scattering Surface

- Anisotropy spectrum today

## 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

## 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

## An infinite number of violins are synchronized 

- Similarly, all modes corresponding to first trough are in phase: they all have zero amplitude at recombination

## Without coherence:

- First “Peak”

- First “Trough”

## When we see this, we conclude that modes were set in phase during inflation!

- Bennett et al. 2003

## Three Step argument for <TE>

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

## Isotropic radiation field produces no polarization after Compton scattering

*Modern Cosmology: *February 21, 2003
- Adapted from Hu & White 1997

- Radiation with a dipole produces no polarization

- A quadrupole is needed

## Quadrupole proportional to dipole

- Dipole is out of phase with monopole

- Roughly,

- 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.

## DASI initially detected TE signal

- Kovac et al. 2002

## WMAP has indisputable evidence that monopole and dipole are out of phase

- This is most remarkable for scales around l~100, which
- were not in causal contact at recombination.

- Kogut et al.
- 2003

## WMAP gets a better fit with spectral index n not constant: A “running” spectrum

- The Age of sifting through inflationary models has begun

## Expand the spectral index about a pivot point:

- If this  is of orderthen  this is typically of order 2  where  is some small number.

## Not many slow roll models have running this large with n-1 this small.

- n

- n’

- Perhaps this is points to particular class of models

- Peiris et al. 2003

## 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.

## Wisecrack example: n’’=-n’

## Morals

- Only a model allows extrapolation past the data (k=1 Mpc-1 ).
- It’s 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)

## Other Random Thoughts

- Is2  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.]

## Conclusions

- Wow!

## Parameters I

- Reionization lowers the signal on small scales
- A tilted primordial spectrum (n<1) increasingly reduces signal on small scales
- Tensors reduce the scalar normalization, and thus the small scale signal

## 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