# Presentation: 073753

## What can we Learn about Neutrinos from Large Scale Structure?

- The Power Spectrum
- Probes of the Power Spectrum
- Degeneracies
- Results
- The Future

- Scott Dodelson
- Neutrinos: Data, Cosmos and Planck Scale
- March 3, 2003

## Why do Neutrinos affect large scale structure?

- We know the neutrino abundance in the universe:
- Neutrinos stream out of overdense regions when T ~ 1 eV.
- Less clustering in universe with massive neutrinos

*The Power Spectrum*

## Quantitative Measure: Power Spectrum

*The Power Spectrum*

## Musical Acoustics

- Middle C
- Middle C on a piano

*The Power Spectrum*

- CMB Anisotropies

*Probes of The Power Spectrum*

## Galaxy Distribution

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

*Probes of The Power Spectrum*

- Percival et al. 2002

## Galaxy Distribution

- Sloan Digital Sky Survey will eventually get redshifts of close to a million galaxies
- Photometry and spectroscopy done in same survey: helps with systematics

*Probes of The Power Spectrum*

- Tegmark et al. 2003

*Probes of The Power Spectrum*

- 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

*Probes of The Power Spectrum*

- Tegmark et al. 2003

- Corrects for this effect

## Lyman Alpha Forest

*Probes of The Power Spectrum*

- QSO Absorption spectra: Regions with depleted flux
- correspond to excess neutral hydrogen

- Croft et al 2002

- Lyman Alpha Forest

*Probes of The Power Spectrum*

- Croft et al. 2002

-  Use simulations to estimate3D matter power spectrumfrom observed 1D flux spectrum

- 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

*Degeneracies*

-  This is virtually degenerate with non-zero neutrino mass

*Degeneracies*

*Modern Cosmology (2003)*

- Scale Factor

- Gravitational Potential

-  Net result: suppression of power as matter density decreases

## CMB

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

*Degeneracies*

*Modern Cosmology (2003)*

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

- Running complicates things

*Degeneracies*

## Running is degenerate with neutrino mass

*Degeneracies*

*Abazajian, Dodelson, & Gates (2003)*

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

*Results*

*Elgaroy et al. (2002)*

## WMAP Spectra

*Results*

*Bennett et al. (2003)*

-  Position and height of firsttwo peaks pinned down
-  Polarization helps by determining extent of reionization

##  WMAP: Matter Density

*Results*

*Page et al. (2003)*

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

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

*Results*

- Spergel et al. (2003)

*Results*

- Croft et al. (2002)

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

## Running and Neutrino Mass

*Results*

- Abazajian, Dodelson, & Gates (2003)

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

## Weak Gravitational Lensing

*Future*

- Unlike galaxy surveys and Lyman alpha, lensing
- directly probes mass distribution!

## Weak Lensing

*Future*

- Abazajian & Dodelson (2002)

- 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!

## Conclusion

- Cosmological constraints on neutrino mass (<0.7eV total) arise from *power spectrum** *
- Wide variety of techniques/experiments needed to eliminate systematics/degeneracies
- We must all become familiar with: inflation, CMB, LSS, dark energy, ... in addition to smooth cosmology ...