# Presentation: 444586

## Running, CMB and the Lyman Alpha Forest

-  Inflation: Is running reasonable?
-  Sloan Digital Sky Survey: Lyman alpha forest

- Scott Dodelson
- Workshop on CMB, Minnesota
- March 19, 2003

*With: **Kev Abazajian, Evalyn Gates, Ewan Stewart,*
*                        **Lam Hui, Adam Lidz*

## Evidence for running comes from CMB on large scales and Lyman alpha forest on small scales

## Even physicists not interested in inflation should care about running. 

- Running is degenerate with neutrino mass

## Running and Neutrino Mass

- Introducing running as an additional free parameter loosens bound on neutrino mass.

## Inflationary models predict little running

- E.g. chaotic inflation with 4 potential

- Deviations from scale invariance represent the first term in the slow roll expansion

- N=number of e-folds
- prior to end of inflation, of order 60

## 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.

## SDSS: Lyman Alpha Forest

- 3000 QSOs withabsorption lines from redshifts 2 to 4.2

- Hui et al.

## 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.

## 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!

## 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)

## 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
- ▪ Consistent with no running

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

## Conclusion

- Large running unlikely from inflation. If running (n’) is large, why not jerking (n’’)?* *
- SDSS superb probe of Ly-alpha: preliminary results consistent with Croft amplitude, but with shallower slope. Very preliminary results: no running
- We must all become familiar with: inflation, CMB, LSS, dark energy, polarization, ... in addition to smooth cosmology ...