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Non-gaussianity, isocurvature, dark matter, and the curvaton modelPowerPoint Presentation

Non-gaussianity, isocurvature, dark matter, and the curvaton model

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### Non-gaussianity, isocurvature, dark matter, and the curvaton model

Phys Rev D 78, 023530, arXiv:0804.1097

Maria Beltran

University of Chicago, KICP

Cosmo 08, 26 August 2008

Non-gaussianity analyses

ZERO WAS EXCLUDED!!

… subsequent analyses

- WMAP 5-year analysis:

-9<fNL<111 at 95% cl

Komatsu et al, arXiv:0803.0732 [astro-ph]

- Non-gaussianity using LSS:

-29<fNL<70 at 95% cl

Slosar et al, arXiv:0805.3580 [astro-ph]

fNL=236±127 at 68% cl

Afshordi and Tolley, arXiv:0806.1046 [astro-ph]

What if fNL~100?

Possible explanations

- Features in the potential.
- Non-canonical term in the Lagrangian of .
- Departure from Bunch-Davies vacuum.
- Multi field inflation.
- …

Possible explanations

- Features in the potential.
- Non-canonical term in the Lagrangian of .
- Departure from Bunch-Davies vacuum.
- Multi field inflation.
- …

The curvaton hypothesis:

*

,

The curvaton modelLinde & Mukhanov, Phys.Rev.D56:535-539,1997

Enqvist & Sloth, Nucl.Phys.B626:395-409,2002

Lyth & Wands Phys.Lett.B524:5-14,2002

Two fields during inflation, only one inflates.

Inflationary constraints

The curvaton model

Lyth, Ungarelli & Wands Phys.Rev.D 67, 023503 (2003)

Because of the presence of the second field, the curvature perturbation is not constant.

Even if we started out with very small curvature perturbation, the observed power spectrum arises due to Pnad.

(sudden decay approximation)

Observable power spectrum:

The curvaton model: Non-gaussianity

Recall the definition:

Relates the ratio of energy densities

at decay, r, to the non-gaussianity

in the primordial power spectrum.

Implications of fNL≈100:

The curvaton model II: isocurvature

- Two decoupled fluids watch out for entropy perturbations.

out

?

L. Amendola et al,

Phys. Rev. Lett. 88 211302 (2002)

The curvaton model II: isocurvature- Two decoupled fluids watch out for entropy perturbations.

- Three different scenarios:
- CDM created after the curvaton decays.
- CDM created much before the curvaton decays.
- The curvaton decays into the dark matter.

The curvaton model II: isocurvature

- Current isocurvature bounds:

E. Komatsu et al, arXiv:0803.0732 [astro-ph]

The curvaton model:isocurvature and non-gaussianity

From high fNL:

From isocurvature:

If we are willing to explain large fNL with the curvaton, we must make sure no isocurvature is generated!

More on the curvaton model

- CDM created after the curvaton decays.
- CDM created much before the curvaton decays.
- The curvaton decays into the dark matter.

- The curvaton will generate the required phenomenology
- If no isocurvature arises. This implies:
- The curvaton cannot decay into the DM
- The DM must decouple after the curvaton has decayed:
Hcdm<Hdec=

More on the curvaton model

- We study to see how tightly we can constrain mcdm.

- Standard assumptions:
- doesn’t drive inflation.
- doesn’t oscillate at the end of inflation.
- doesn’t drive a second inflationary period.

- Additional constraints:
- is an almost massless scalar field during inflation.
- The amplitude of the power spectrum.
- Value of the spectral tilt 0.93< ns <1.

Results

M. Beltran, PRD, arXiv:0804.1097 [astro-ph]

- Very mild dependence on the precise value of fNL (b = 0.1)

H*=1012 GeV

H*=1010 GeV

H*=109 GeV

The predictions are robust against variation of assumptions

Conclusion

- Exciting, recently accessible, cosmological observable.
- If fNL≥O(10) we’d better explain.
- The curvaton model could fit the requirements,then:
- The curvaton cannot decay into DM.
- DM must be created after the curvaton decays.

- These two conditions constrain the nature of DM and inflationary parameters:
- Absolute upper bound for Tcdm (Tcdm<107 GeV for m22).
- Unique link between H* and the mass of a DM.

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