1. Small scale modifications to the power spectrum and 21 cm observations Kathryn Zurek University of Wisconsin, Madison

2. Small Scale Power and 21 cm Outline What we know about the DM and what we expect What we know about the DM and what we expect Modifications to small scale power Modifications to small scale power Particle physics models which produce Particle physics models which produce Small scale suppression Small scale suppression Small scale amplification Small scale amplification Implications for structure formation and 21 cm Implications for structure formation and 21 cm

3. Dark Matter: what do we know? Spectrum determined only by inflationary perturbations Macroscopically, dark matter observed as cold, collisionless For most dark matter candidates, the microscopic nature of the dark matter only imprints itself on very small scales WIMP Axion Tegmark and Zaldarriaga

4. Modifications to small scale power Primordially warm sterile neutrinos (Dodelson and Widrow, Abazajian et al.) Late-decaying particles (e.g. Super-WIMPs, Feng et al. and meta-CDM, mCDM Strigari et al.) Late kinetic decoupling between DM and neutrinos keeps the DM warmer Implications for structure on small scale (i.e. less of it) Loeb and Zaldarriaga, astro-ph/0504112

5. DM and Late Kinetic Decoupling Scattering off neutrinos keeps DM warm Scattering off neutrinos keeps DM warm Right relic abundance Right relic abundance Explain 511 keV line toward the center Explain 511 keV line toward the center Hooper, Kaplinghat, Strigari, Zurek arXiv:0704.2558 Boehm, Hooper, Silk, Casse, Paul, PRL, astro-ph/0309686; Boehm and Fayet, Nucl. Phys. B, hep-ph/0305261

6. Damping small scale power Exactly the right scale to solve the missing satellite problem! Warm DM limit (Ly-  ) m  =1 MeV, T kd =1 keV, 10 keV Hooper, Kaplinghat, Strigari, Zurek

7. Observing small scale power with 21 cm May reach to smaller scales on account of less gas heating at high redshifts May reach to smaller scales on account of less gas heating at high redshifts Optical depth for absorption in 21 cm prop to density  absorption depends on density fluctuations Optical depth for absorption in 21 cm prop to density  absorption depends on density fluctuations Loeb and Zaldarriaga

8. Different Modification to small scale power: white noise from dark matter E.g. Primordial Black Holes Poisson noise imprints fluctuations Constrain mass of objects from power spectrum Afshordi et al. astro-ph/0302035 Zurek et al. astro-ph/0607341

9. Dark matter dynamics can also imprint Poisson noise on power spectrum Axion-like field Each Hubble patch has a different dark matter density On larger scales density fluctuations are Poisson noise

10. Dense objects on small scales Zurek, Hogan, Quinn, astro-ph/0607341 Non-linear density fluctuations! Kolb and Tkachev, astro-ph/9510043

11. Modified history of structure formation on small scales Dark matter collapses and virializes sooner (on small scales) Early baryon collapse? Earlier star formation? Modified reionization history? From dark matter dynamics consistent with current data! Zurek and Hogan astro-ph/0703624

12. Optical depth: more absorption in 21 cm due to higher densities on smaller scales Optical depth: more absorption in 21 cm due to higher densities on smaller scales 21 cm may also look for modified histories 21 cm may also look for modified histories Early gas heating Early gas heating Collisions excite the hyperfine state Collisions excite the hyperfine state Information encoded in the spin temperature Information encoded in the spin temperature Implications for 21 cm Collisions or background photons n1n0n1n0

13. CDM and 21 cm High densities: spin temperature set by collisions Low densities: spin temperature set by background photons Photon temperature Spin temperature Kinetic temperature

14. Deviations from CDM Modified power spectrum  Modified structure formation  Modified structure formation  Modified history of baryon collapse  Modified history of baryon collapse  Modified history of gas heating  Modified history of gas heating  Modified spin temperature history  Modified spin temperature history Hotter gas, higer kinetic temperature Less gas heating, less power on small scales Zurek and Hogan astro-ph/0703624

15. Summary 21 cm emission may measure modified small scale power directly 21 cm emission may measure modified small scale power directly Test models of warm DM, lately heated DM, DM with late kinetic decoupling Test models of warm DM, lately heated DM, DM with late kinetic decoupling WIMPs and axions are not the only DM candidates on the market! WIMPs and axions are not the only DM candidates on the market! 21 cm may also look for modified history of structure formation, gas heating 21 cm may also look for modified history of structure formation, gas heating Modified histories may be signal for exotic DM dynamics Modified histories may be signal for exotic DM dynamics