Probing the Dark Sector

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 • 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 77 024048 (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 • 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, http://arxiv.org/abs/0808.1105

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

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

17. DM Work: Results • At 95% confidence <3.9 for 1 Mpc, and <1.05 at 10 Mpc

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