The Shadow of Dark Matter

1. The Shadow of Dark Matter Kris Sigurdson Institute for Advanced Study Hubble Symposium 2007 Space Telescope Science Institute April 2, 2007

2. Overview • Motivation • Dark Matter is ‘Dark’ • The Model • Constraints • An Observable Effect? • Particle Physics Setups • Conclusions Stefano Profumo and KS: Phys. Rev. D75 023521 (2007) astro-ph/0611129

3. Motivation • But… we don’t know much about the physics of dark matter. • Worth thinking about alternative avenues of discovery.

4. Dark Matter Dark Matter Dark Matter ‘Dark’ Matter is Dark Matter Not Dark Matter Photos: Martin White’s Webpage

5. Dark Matter Dark Matter ‘Dark’ Matter is Dark Matter ? Not Dark Matter

6. ‘Dark’ Matter is Dark Matter • Very weak coupling to photons • Strong Limits: Charge (e.g. A. Gould et al. 1990) Milli-Charge (e.g. S. Davidson et al. 2000; S. Dubovsky et al. 2004) Magnetic/Electric Dipole (e.g. KSet al. 2004) • Can NOT appreciably scatter light because the coupling is so very weak

7. S. Profumo CALTECH Can Dark Matter Cast a Shadow? ? g g (?) Dark Matter Observer Photon Source

8. The Model • Stable Neutral Dark Matter Particle • Unstable Neutral Heavier Particle • Coupled to Photons and each other via a Transition Magnetic/Electric Moment

9. The Model “Atom-like interaction”

10. The Model: Resonant Scattering

11. Resonant Photon Scattering Relativistic Breit-Wigner Cross Section CM Momentum CM Energy Squared

12. S. Profumo CALTECH Can Dark Matter Cast a Shadow? ? g g (?) Dark Matter Observer Photon Source

13. The Parameters

14. Constraints • The coupling can allow for production of pairs • Existing astrophysical constraints on Milli-charge (fractional charge) particles (e.g. G. Raffelt 1996) • Apply, but replace with:

15. Lyman- • But…. constraints from the Lyman-forest on warm dark matter impose: • This supercedes the stellar energy loss limit for the relevant region of the parameter space unless the dark matter is produced in a nonstandard way

16. The Constraints

17. SN1987A • Excess production of pairs in SN1987A SN Core Plasma Frequency Excludes: (Too Much Energy Loss) (Particles Trapped)

18. The Constraints

19. Big Bang Nucleosynthesis • If thermalized in the early Universe around BBN and would contribute to the number of light degrees of freedom present during BBN Excludes:

20. The Constraints

21. “Running” of em • In the standard model the strength of the electromagnetic interaction becomes stronger at higher energies Modifies the Running of  up to the Z-pole Must Have:

22. The Constraints

23. Accelerators

24. The Constraints

25. S. Profumo CALTECH Can Dark Matter Cast a Shadow? ? g g (?) Dark Matter Observer Photon Source

26. Velocity Broadening • Dark matter particles live in a halo with a nonzero virial velocity dispersion Maxwell-Boltzmann:

27. Broadening in DM Halos Coma-like Broadened

28. The Opacity In Detail: DM Surface Density The Optical Depth

29. An Absorption Feature? • The dynamics of the scattering process ~ Compton scattering forward scattering is unlikely: if a photon scatters, it’s lost (scattering=absorption) • Absorption occurs if t ~ 1 Can  be large enough?

30. An Absorption Feature? • Consider a cluster like the Coma Cluster: Estimate  ~ 5x1029 MeV/cm2 for a LOS through cluster center • Consider a source behind or at the center of the cluster (e.g. a quasar)

31. Absorption Feature? Vary Intrinsic Width LOS through Center

32. Potentially Interesting Targets? • Perhaps: Active Galactic Nuclei (e.g. Centaurus A or M87). With a “DM spike”. • Perhaps: Gamma Ray Bursts? With the right LOS. • Statistical Detection?

33. S. Profumo CALTECH “Viable” Parameter Space Region Summary: The (,m2) Plane “Coma” reference surface density giving t ~ 1

34. Summary For: Mass Range: Resonant Energy:

35. Other observables: Annihilation? • Through the same interaction Dark Matter particles could annihilate to monochromatic photons

36. Annihilation: Flux Expected Flux: Diffuse Gamma from COMPTEL/EGRET: Unfortunately: Difficult to detect such a line from the Galactic center. Perhaps: Dwarf galaxies (e.g. Profumo and Kamionkowski 2006) *Dedicated line search by INTEGRAL-SPI also not sensitive enough (Teegarden and Watanabe 2006)

37. Supersymmetric Absorption? • SUSY: Neutralino Dark Matter • In principle: could construct such a model in a SUSY setup with lightest neutralino and next-to-lightest neutralino Too low number density for a detectable signal

38. Extended MSM? • MSM: DM abundance, neutrino masses, baryon asymmetry, potentially inflation (T. Asaka et al. 2005; M. Shaposhnikov 2006) • MeV mass dark-matter • Extending this with the transition-moment interactino could lead to the phenomenology discussed here

39. The End • Dark Matter is ‘Dark’ Matter… but for special energies resonant scattering is possible • a priori: This could lead to absorption features due to dark matter halos. • A range of the parameter space remains. • Perhaps: AGN, GRBs, ???? • Not SUSY. Perhaps MSM-like model. Stefano Profumo and KS: Phys. Rev. D75 023521 (2007) astro-ph/0611129