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

2007/09/11TAUP Sendai2 Brief review… Much evidence for its existence, but their true nature is unknown Is it a particle (WIMP)? Extensions of SM predict weakly interacting particles that has the right properties, e.g. the Neutralino Search for new particles as dark matter candidates Fundamental Question ： what is dark matter ? Indirect detection: detect signatures of pair- annihilation Photons, neutrinos, etc Annihilation rate ∝  2

2007/09/11TAUP Sendai3 Where do we observe? Places where the dark matter is strongly concentrated, for example: –Galactic centre Bengtsson et al.‘90, Berezinsky et al. ’94, … –near black holes Gondolo&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

2007/09/11TAUP Sendai4 Galactic Centre Flux of dark matter annihilation signal well studied [ Bengtsson et al (‘90), Berezinsky ’94, Bergstrom & Ullio (‘97), etc ] DM particle properties DM density distribution i = ,, e, p, … Normalizing the line of sight integral to the solar dark matter density J s, we can define J : Region of interest m > O(100) GeV dimensionless enhancement factor

2007/09/11TAUP Sendai5 Galactic Centre (2) GC flux predictions can vary considerably ProfileγAve J Moore1.53×10 4 NFW Kra0.730 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 ]

2007/09/11TAUP Sendai6 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…are there other regions where the flux and background are better known?

2007/09/11TAUP Sendai7 Field of View The Whole Milky Way? Model ~1 deg~30 deg ~180 deg Anti- GC Moore 3× NFW Kra Average enhancement (J) for different profiles and FOVs: Consider a larger field of view – the entire Milky Way halo Define: Halo Angular Halo Average Halo Isotropic More profile independent

2007/09/11TAUP Sendai8 Flux strength For illustration, consider Neutralino →  rays Use NFW Normalize to the GC flux Halo Isotropic component is as large as (or larger than) the truly cosmic component! Flux smaller…but more robust, and less background.

2007/09/11TAUP Sendai9 Assuming that only neutrinos are produced (i.e.   ), from the null detection in the atmospheric neutrino background, they placed a model independent limit of  v < cm 3 s -1 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 ] noted that given something is produced, the hardest to detect particle will set the uppermost limit. SM particles; “visibile” + “invisible”

2007/09/11TAUP Sendai10 Neutrino Bound (2) Atmospheric muon neutrino from Frejus, Super-K, AMANDA (ignore angular dependence) Use Energy bins of:  log E = 0.3 [Halo]  log E = 0.5 [Cosmic] Detection requirement: signal is double background Previous neutrino bound considered the cosmic dark matter annihilation signal. We extend this by considering annihilation from the Milky Way Halo

2007/09/11TAUP Sendai11 Improved Neutrino Bound This is good because: 1. the fluxes are larger 2. it relies on different physics and is more robust Halo Isotropic previous cosmic consideration Whole Milky Way halo Mass [GeV]

2007/09/11TAUP Sendai12 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 ]