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Dark Matter Annihilation in the Milky Way Halo

Dark Matter Annihilation in the Milky Way Halo. Shunsaku Horiuchi (Tokyo) ------- Hasan Yuksel (Ohio State) John Beacom (Ohio State) Shin’ichiro Ando (Caltech). arXiv:0707.0196, PRD submitted. Brief review…. Much evidence for its existence, but their true nature is unknown.

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Dark Matter Annihilation in the Milky Way Halo

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  1. Dark Matter Annihilation in the Milky Way Halo Shunsaku Horiuchi (Tokyo) ------- Hasan Yuksel (Ohio State) John Beacom (Ohio State) Shin’ichiro Ando (Caltech) arXiv:0707.0196, PRD submitted

  2. Brief review… Much evidence for its existence, but their true nature is unknown Indirect detection: detect signatures of pair-annihilation Fundamental Question：what is dark matter ? Is it a particle (WIMP)? Extensions of SM predict weakly interacting particles that has the right properties, e.g. the Neutralino Photons, neutrinos, etc Search for new particles as dark matter candidates Annihilation rate ∝r2 TAUP 2007 @ Sendai

  3. Where do we observe? Places where the dark matter is strongly concentrated, for example: • Galactic centreBengtsson et al.‘90, Berezinsky et al. ’94, … • near black holesGondolo&Silk ’99, Bertone et al. ’05, … • Dwarf satellite galaxies, e.g. DRACO Bergstrom ‘06, Profumo ‘06 • Nearby galaxies, e.g. M31 • Extragalactic Ullio et al. ’02, … • Microhalos Narumoto&Totani ’06 Diemand et al. 2007 TAUP 2007 @ Sendai

  4. Galactic Centre Flux of dark matter annihilation signal well studied [Bengtsson et al (‘90), Berezinsky ’94, Bergstrom & Ullio (‘97), etc ] i= g, n, e, p, … DM density distribution DM particle properties Normalizing the line of sight integral to the solar dark matter density Js, we can define J : Region of interest m > O(100) GeV dimensionless enhancement factor TAUP 2007 @ Sendai

  5. Galactic Centre (2) GC flux predictions can vary considerably Inner (<1pc) profile uncertain: • N-body simulations generally predict a cusp • observations show no clear evidence of a cusp/core This causes a large difference. Also, • effects of baryons [Prada ‘04] • background [Zaharijas ‘06] TAUP 2007 @ Sendai

  6. Uncertainties As we’ve seen, dark matter concentrations increase the annihilation rate  good for detection. But distribution uncertainties cause large uncertainties ( > order magnitude) in the predicted flux. • Galactic Centre: cusp/core problem, effects of baryons, large astrophysical background • Near BHs: Formation and survivability of spikes (Ullio+’05) • Extragalactic signal：mass-function cut-off, concentration parameter To obtain constraints from null detections, we want to minimize the uncertainties caused by dark matter distribution…arethere other regions where the flux and background are better known? TAUP 2007 @ Sendai

  7. Field of View The Whole Milky Way? Consider a larger field of view – the entire Milky Way halo Average enhancement (J) for different profiles and FOVs: More profile independent Define: Halo Angular Halo Average Halo Isotropic TAUP 2007 @ Sendai

  8. Flux strength For illustration, consider Neutralino →g rays Use NFW Normalize to the GC flux Flux smaller…but more robust, and less background. Halo Isotropic component is as large as (or larger than) the truly cosmic component! TAUP 2007 @ Sendai

  9. Neutrino Bound There are numerous dark matter candidates (or “models”) dN/dE varies between models. How do we then place a model independent constraint on the total annihilation cross section? Ref [Beacom et al. 2006] noted that given something is produced, the hardest to detect particle will set the uppermost limit. c SM particles; “visibile” + “invisible” c Assuming that only neutrinos are produced (i.e. cc  nn), from the null detection in the atmospheric neutrino background, they placed a model independent limit of sv < 10-21 cm3s-1 TAUP 2007 @ Sendai

  10. Neutrino Bound (2) Previous neutrino bound considered the cosmic dark matter annihilation signal. We extend this by considering annihilation from the Milky Way Halo Atmospheric muon neutrino from Frejus, Super-K, AMANDA (ignore angular dependence) Use Energy bins of: Dlog E = 0.3 [Halo] Dlog E = 0.5 [Cosmic] Detection requirement: signal is double background TAUP 2007 @ Sendai

  11. Improved Neutrino Bound Halo Isotropic previous cosmic consideration Whole Milky Way halo This is good because: 1. the fluxes are larger 2. it relies on different physics and is more robust Mass [GeV] TAUP 2007 @ Sendai

  12. Conclusions • Uncertainties in the dark matter distribution make constraining dark matter particle properties hard. • We analyzed the Milky Way halo to show that: • Uncertainties in the predicted annihilation flux are reduced considerably by observing larger FOVs • The galactic halo isotropic component is larger than the truly cosmic signal • Using the Milky Way halo components, we improved the previous Neutrino bound by 1-2 orders. • Dedicated analysis using better Energy resolution and better criteria, angular dependency, can further improve the Neutrino bound. [Kachelriess 2007] TAUP 2007 @ Sendai

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