# Presentation: 146437

## Cosmological Puzzles

- Sloan Digital Sky Survey
- SDSS vs. LSND
- SDSS vs. WMAP
- SDSS vs. SDSS

- Scott Dodelson
- Tropical Workshop on Particle Physics and Cosmology
- June 13, 2003

## Sloan Digital Sky Survey

-  2.5 meter telescope in Apache Point, New Mexico
-  Collaboration of: Fermilab, Princeton, U. Chicago, U.Washington, Johns Hopkins, New Mexico State, Max Planck, Japan, Pittsburgh, ...
-  Scheduled to end in 2005; may be extended until 2007; will cover 1⁄4 of the sky

## Two surveys in one

-  Photometric survey: hundreds of millions of objects in 5 bands
-  Spectroscopic survey: ~1 million objects with spectra
-  Spectroscopic survey targets objects found in photometric survey. Reduces systematic effects (typically objects targeted for redshifts are found in different survey, leads to complicated selection function).

## 5 Filters very efficient 

- Ultimately will get redshifts for ~750,000 galaxies; 100,000 QSOs

- I’ and z’ bands especially important for high redshift QSOs. Lyman alpha line (1215Ang) redshifted to 1215*(1+z) Ang. Can get z>6 QSOs.

## Coherent picture of formation of structure in the universe

- Quantum      Mechanical Fluctuations during Inflation

- Perturbation Growth: Pressure vs. Gravity

- t~100,000 years

- Photons *freestream: *Inhomogeneities turn into anisotropies

- Matter perturbations grow into non-linear structures observed today

## By studying structure in the universe, we can learn about:

- Constituents of the universe: baryons, radiation, neutrinos, and cold dark matter
- Re-ionization history
- Dark energy and its equation of state
- Inflaton potential: physics at GUT scales

## 1. What are the neutrino masses?

*KARMEN collaboration 2002*

- SDSS has something to say about this because ...Mass distribution in the universe depends on neutrino mass

## Neutrino mass affects large scale structure

- Neutrinos stream out of overdense regions when t ~ 100,000 years.
- We know the (standard) neutrino number density in the universe:
- Massive neutrinos eliminate small scale power

## Quantitative Measure: Power Spectrum

## Power spectrum depends only on massive neutrino energy density

- Sterile  typically thermalize (*Abazajian, 2002*) so cosmological constraints apply (but see *Foot & Volkas, 1997*)

## Degeneracies

-  Lowering the matter density suppresses the power spectrum
-  This is virtually degenerate with non-zero neutrino mass

## Why does small matter density reduce clustering?

*Dodelson, Modern Cosmology (2003)*

- Scale Factor

- Gravitational Potential

-  Potential wells decay for sub-horizon modes in radiation era
-  Decreased matter density  later epoch of equality * *more decay
-  Net result: suppression of power as matter density decreases

##  WMAP: Matter Density

*Page et al. (2003)*

-  First peak position determinescombination of matter densityand Hubble constant
-  Height of first peaks determineseach separately

## Galaxy Distribution

- Large surveys with >200k galaxy redshifts: 2dF and SDSS
- 2dF takes redshifts of galaxies first observed by APM
- Restrict to linear scales

- Percival et al. 2002

## Galaxy Distribution

- Sloan Digital Sky Survey has now analyzed data with 144k redshifts
- Photometry and spectroscopy done in same survey: helps with systematics

- Tegmark et al. 2003

- Fainter                                       Brighter 

-  Less Clustered          More clustered 

- One systematic: luminosity bias
- Intrinisically brighter galaxies are seen at large distances (cause faint ones can’t be seen)
- These determine large scale power spectrum
- Since these are more clustered, large scale spectrum is biased high!
- Conversely, small scale spectrum is biased low!

## Luminosity Bias

- Tegmark et al. 2003

- Corrects for this effect

## Results

- 2dF + BBNprior
- With no external info on matter density,

*Elgaroy et al. (2002)*
*Elgaroy & Lahav (2003)*

## Results

- WMAP + 2dF + small angle CMB +  Lyman alpha

- Spergel et al. (2003)

## Weak Gravitational Lensing

- Unlike galaxy surveys, lensing directly probes mass distribution!

## Weak Lensing

- Abazajian & Dodelson (2003)

- Measure power spectrum AND/OR measure growth of spectrum at late time
-  Sensitive to neutrino mass AND dark energy
-  Ergo, accelerator neutrino experiments will teach us about dark energy!

## 2. How/when did hydrogen get ionized?

- SDSS has something to say about this because ...Light from very distant QSOs gets absorbed by neutral hydrogen along line of sight

*Becker et al. 2001*

## High z QSOs look red!

## High Redshift QSO’s

- Fan

## SDSS determined the epoch of reionization

*White et al. 2003*

- There was a lot of neutral hydrogen at z > 6. There was much less at later times.

## WMAP determined epoch of reionization

- Reionization induces scattering off quadrupole, leading to polarization. The earlier the reionization the larger the signal.

*Kogut et al. (2003)*

## First thought: This is impossible

## Second thought: This is easy

## Last thought: This is hard!

- Haiman & Hui, 2003

- Reionization heats up cosmic plasma
- It had to  occur recently, or temperature would be too low

## Future: 3-pronged approach

- CMB polarization and small angle anisotropy sensitive to reionization, goes forward from z=17
- James Web Space Telescope (formerly NGST), goes backwards from z=6
- Simulations improving

## 3. What does the inflaton potential look like?

- SDSS has something to say about this because ...
- it can measure the power spectrum with the Lyman alpha forest, increasing the range of scales over which it is measured.
- Inflaton potential determines shape of primordial spectrum

## Flat potential → Scale-Invariant Spectrum

- E.g. chaotic inflation with 4 potential

- Running (non-zero n’) should be small, but WMAP claimed 2-sigma detection.

-  describes deviations from flat potential

- Typically, n is close to 1

## Lyman alpha forest

- Photons with energy > (n=1 to n=2 transition energy) get absorbed along the line of sight as they lose energy due to cosmic redshift.
- Every absorbtion line corresponds to *cloud* of neutral hydrogen.

## Fluctuations in density mimicked by fluctuations in forest

*Gnedin & Hui, 1997*

## SDSS: Lyman Alpha Forest

- 3000 QSOs withabsorption lines from redshifts 2 to 4.2

*Hui et al., 2003*
*Seljak et al., 2003*

## Goal: 1D Flux power spectrum

-  Subtract mean flux and divide by mean flux. This gives open squares]
-  Composite QSO spectrum [crosses]
-  Principle Component Analysis: Allow each QSO spectrum to vary: linear combination of training set [reference points]

- Simple thing works.
- Composite spectrum works very well.

## Systematics Check

- Cross-correlate distant lines of sight. No intrinsic correlations: any observed must be due to improper continuum fitting.

- Possible problems on large scales. No problems on small scales.

- Sophisticated estimate

- Simple continuum estimate

## Results

-  Dashed lines are from Keck;solid from SDSS
-  3 sets of curves from low (bottom) to high (top) redshift
-  SDSS goes to larger scales, but doesn’t have small scales resolution

- Good agreement with Keck!

## Convert 1D Flux Spectrum to 3D Linear Matter Power Spectrum

- Run many simulations with CDM-like spectra
- Extract Flux power spectra from each simulation
- Fit amplitude and slope of power at 1 Mpc

- Lidz et al.

## Mild Evidence for Linear Growth

## 3D Linear Power Spectrum

## Constraints on running

- ▪ WMAP+ACBAR+CBI+ SDSS Lyman alpha
- ▪ 7 cosmological parameters

- Abazajian et al (March 19, 11:10 CST)

- No evidence for running!

## We are investigating source of discrepancy:

- 1-D flux is more difficult to extract than previously thought

## Conclusion

- Tension between cosmological constraints on neutrino mass (<0.7eV total) and hints from LSND
- Reionization began at z=17 but was *not* a simple process
- The inflaton potential may be more complicated than expected
- Thanks to Ray, Stuart, and all the organizers!

## Six more redshift bins

- High z

- Low z

## Parameterize with amplitude at every redshift: scales as (1+z)4

- (Parenthetically: No evidence for Helium reionization)

- CMB Anisotropies

*Probes of The Power Spectrum*

*Modern Cosmology (2003)*

-  Amplitude of given Fourier mode remains constant until horizon entry
-  Upon horizon entry, acoustic oscillations begin

- Fourier amplitude

- Recombination

- Initial amplitude for given k is randomly chosen
- If phase was randomly chosen as well: disaster!

*Probes of The Power Spectrum*

-  “First Peak” Mode                     “First Trough” Mode

- The phases were synchronized when the universe was very young: Inflation
- Detection of peaks and troughs confirm basic model; makes neutrino mass limits more robust

*Probes of The Power Spectrum*

-  “First Peak” Mode                     “First Trough” Mode

## Running and Neutrino Mass

*Results*

- Abazajian, Dodelson, & Gates (2003)

- Very preliminary result: running does alleviate bound on neutrino mass

*Results*

- Croft et al. (2002)

-  Lyman alpha + some info from large scale structure (pre-2dF)+COBE normalization

## For general potentials:

- Unless there is a feature in the spectrum, we expect running (n’) to be of order (n-1)2. If n’ is of order (n-1), then expect n’’ also to be of order (n-1).

- Dodelson & Stewart (2001),Stewart (2001)

## We have no models for inflaton potential

- Circumvent the potential: take initial conditions for slow roll parameters  and evolve (Kinney, 2002)
- Run 1,000,000 models
- Compute observables for every run

## Inflation can generate many different values of n, the spectral index 

## Inflation typically generates n’ very close to zero (WMAP value: -.04)

## If n’ is big, what about n’’?

- 15/million runs which fall within WMAP 1-sigma range

- Suggests: If n’ is large, so is n’’.

## How big is big?

- Recall:
- Require:

- where k1/k0 is the range of scales probed by observations:about four orders of magnitude.

## Musical Acoustics

- Middle C
- Middle C on a piano

## Cosmic Microwave Background

- Decrease in matter density leads to enhanced peaks
- Position of first peak (in flat universe) is affected by matter density
- CMB can break degeneracy

*Dodelson, Modern Cosmology (2003)*