1. Probing the Dark Sector
Istvan Laszlo
Cosmo ‘08
August 28th, 2008

2. The Dark Sector ~95 % of the Universe is stuff we don’t know
~74% Dark Energy (DE)
Accelerated expansion
~21%Dark Matter (DM)
Galactic rotation curves

3. The Simple Picture Together in simplest form get LCDM
Pretty successful, but has issues
DE as Cosmological constant: Fine tuning/coincidence problems
CDM: Matching Observations to Simulations
Cuspiness Problem
Missing Satellite Problem
CDM: Acbar sees an 1.7 sigma detection of excess of power for l>2000 (Reichardt et al. 2008)

4. Outline Looking past L Looking past CDM
Ways to learn about impact of a DE model
Looking past CDM
Setting constraints on a dark matter interaction

5. So what is Dark Energy? Quintessence?
Interaction with Higher Dimensions?
New exotic material?
Modified Gravity?

6. DE as Modified Gravity
Laszlo & Bean, Phys. Rev. D (Jan 30, 2008).
Treat DE as a generally parameterized modified gravity theory as in Stabenau and Jain (2006), and Tsujikawa (2007)
Goal is to simulate affected observables quickly and reliably
matter power spectrum and weak lensing convergence power
Compare fast approach of linear simulation with fits to get to nonlinear power to the reliable approach of full nonlinear simulations (Gravity Only PM code of Klypin and Holtzman, 1997)

7. The Fits Two standard fits They Can modified gravity break the fits?
Smith et. al.
Peacock & Dodds
They
Ultimately both rely on the applicability of the Zel’dovich approximation
Can use linear growth factor and initial displacement to extrapolate to later time.
Fit a transition between purely linear and purely nonlinear scales via simulations of standard gravity
Can modified gravity break the fits?
Change critical density for collapse
Change scale at which nonlinear effects become important

8. Evolution Equations Working in Newtonian Gauge
Poisson’s and Peculiar acceleration equations
where
describes a change in the relationship of potential to over-density such as
and we add some extrinsic shear as

9. Models
Given this parameterization we can incorporate quite a wide range of modified gravity theories
F(R,F,C) (as in Tsujikawa 2007)
Scalar-Tensor theories
Also includes Quintessence, k-essence
We therefore choose 4 models to explore the parameters’ effects

10. DE Models Choose models that involve/are mixtures of
Scale dependent modification to Poisson’s Equation
Scale independent modification to Poisson’s Equation
Scale independent anisotropic shear

11. A Sample Result

12. DE Conclusions
For a wide range of modified gravity theories we can utilize the and parameterization
For things describable by this parameterization, we can use the quick approach to compare theories and observations at least at these scales, ie in the mildly nonlinear regime

13. Interacting DM
Bean, Flanagan, Laszlo, & Trodden,

14. DM Work : Model Consider a Lagrangian for DM of the form
A scalar field mediates interaction via Yukawa coupling
Interaction length scale set by mass of scalar field particle
Relativistic so motion is adiabatic. Thus energy is conserved aside from expansion can show rs=sqrt(energy/numberdens^2/coupling^2)
So E down with exp is ~a^-1 number dens is a^-3 so rs ~ sqrt a^2~a is comoving
L top Freiman and Gradwohl or nUsser Gubser and Peebles

15. DM Work: Model This results in a total potential for the DM with
From which we see that
Thus the growth of perturbations is altered

16. DM Work: Sample CMB
Theta=180/l and L= k\eta, Height difference in peaks indicates baryons.
Peak is remnant harmonic of sound waves first peak at 1 degree or so means flat
Peaks from inflation since suggests in place early as have harmonics and thin peak
Originally all together, neutrino free so flattens out, DM free and no press so sits there grows, Bary and phot move out decouple then bary leaves peak on dm as the two group into sync
Though beta >-0.5 implied by Frieman and gradwohl we take >0 <0 shifts peaks up at highl but doesn’t impact tail reverses the effect or rs to some extent

17. DM Work: Results
At 95% confidence <3.9 for 1 Mpc, and <1.05 at 10 Mpc
Chisquared best was for the yukawa interaction, for standard case. (and mean log like was vs )

18. Conclusions
Cosmological observables can be used effectively as means of probing both components of dark sector
And in particular
For modified gravity we can confidently apply the standard fits (at least for mildly nonlinear scales) and so have a quick way to test models
For DM showed that l>2000 excess in CMB does not favor interacting DM