Enhancement of Antimatter Signals from Dark Matter Annihilation around Intermediate Mass Black Holes Pierre Brun Laboratoire d Annecy-le-vieux de Physique des Particules CNRS/IN2P3/Université de Savoie brun@lapp.in2p3.fr In collaboration with G. Bertone, P. Salati, J. Lavalle, R. Taillet
Outline Indirect search for Dark Matter : principles General discussion about boost factors Intermediate Mass Black Holes in Milky Way sized halos Enhancement of the dark matter annihilation signals by IMBHs P. Brun TeV Particle Astrophysics II at University of Wisconsin 2
Indirect search for dark matter disc ~ 20 kpc Annihilation process Final state halo ~ 200 kpc P. Brun TeV Particle Astrophysics II at University of Wisconsin 3
Indirect search for dark matter disc ~ 20 kpc Annihilation process Final state halo ~ 200 kpc Charged particles e +, p, D γ,ν Production rate : P. Brun TeV Particle Astrophysics II at University of Wisconsin 4
Indirect search for dark matter Annihilation process Final state GLAST disc ~ 20 kpc halo ~ 200 kpc Charged particles e +, p, D γ,ν AMS02 ANTARES PAMELA ICECUBE Production rate : Experiments will look for : Excess Spectral distortions γ lines P. Brun TeV Particle Astrophysics II at University of Wisconsin 5
Example with the Positron Excess hints for an excess in the positron channel (AMS01 & HEAT) : Natural & Optimistic dark matters model too low exotic flux Need for a BOOST FACTOR B.F. is often claimed to be a consequence of DM substructures P. Brun TeV Particle Astrophysics II at University of Wisconsin 6
Propagation of charged particles Dark matter halo Diffusive halo : 20 kpc 200 kpc 6 kpc Magnetic fields Annihilations take place in : Whole halo Galactic center Substructures Particular case : positrons from Kalutza-Klein dark matter 100 GeV e + line P. Brun TeV Particle Astrophysics II at University of Wisconsin 7
Computing the flux from the halo Propagation equation for positrons : =0 Diffusion Energy losses B fields inverse Compton & synchrotron Source New Phys. & halo Boundary conditions Resolution Green function Flux from dark matter annihilations in the halo : P. Brun TeV Particle Astrophysics II at University of Wisconsin 8
Dealing with substructures Dark matter substructures could be brighter than the halo About Substructures : LARGE UNCERTAINTIES Consider a local over-density of dark matter : ρ² A boost factor is often introduced : ρ² ad hoc number energy independent not computed r The ratio of these areas defines the source boost factor B 0 r B 0 is defined with respect to some reference density ρ 0 It is no the effective boost factor P. Brun TeV Particle Astrophysics II at University of Wisconsin 9
The effective boost factor Total flux at the Earth : φ i being the flux from a single over-density Effective boost factor : Finally : Normalization factor = flux from the smooth halo Green function describes the propagation of e + Integral over the substructure volume B 0 The boost factor depends on : The energy, via I and G The considered cosmic ray specie, via G ( G e+ G p G D ) The internal structure of the over density, via B 0 Their location in the Milky Way, via G P. Brun TeV Particle Astrophysics II at University of Wisconsin 10
The energy dependence of the boost factor Positron loose energy as they propagate : The more is it detected close to its initial energy, the more close it comes from E 1 J. Lavalle, J. Pochon, P. Salati, R. Taillet (2006) E 2 >E 1 The sensitivity sphere radius is shortened as E The positrons comes from the volume V s : E V s P. Brun TeV Particle Astrophysics II at University of Wisconsin 11
Prediction of the Effective Boost Factor We wish make a prediction on the value of B : Statistical analysis Assume a statistical repartition of substructures Compute the random flux mean value and dispersion The prediction of B is affected by galactic variance P. Brun TeV Particle Astrophysics II at University of Wisconsin 12
Prediction of the Effective Boost Factor General proceedure : Cosmological simulation are performed Number of substructures in the halo Internal structure (related to the source boost factor) Spatial distribution Analytical determination of the expected<b> Analytical determination of the variance (when possible) Monte Carlo simulations <B>, σ B P. Brun TeV Particle Astrophysics II at University of Wisconsin 13
Boost factor from clumps Inputs : Internal structure of clumps Mini halos with NFW profiles, M clumps = [ 10 4, 10 6 ] M Amount of clumped halo mass Fixed fraction of clumpy mass gives the total number of clumps Spatial distribution Follows the whole dark matter density Particle physics framework 100 GeV positron line (Kalutza-Klein models) with σv=10-26 cm 3.s -1 P. Brun TeV Particle Astrophysics II at University of Wisconsin 14
Boost factor from clumps J. Lavalle, J. Pochon, P. Salati, R. Taillet (2006) 20% clumpy halo Mean value of 0(10) Depends on the energy depends on the halo profile (reference) Light clumps : higher number smaller variance Heavier clumps : smaller number higher variance P. Brun TeV Particle Astrophysics II at University of Wisconsin 15
Boost factor from clumps J. Lavalle, J. Pochon, P. Salati, R. Taillet (2006) 20% clumpy halo Mean value of 0(10) Depends on the energy depends on the halo profile (reference) Light clumps : higher number smaller variance Heavier clumps : smaller number V s decreases as E increases σ B higher variance P. Brun TeV Particle Astrophysics II at University of Wisconsin 16
Intermediate Mass Black Holes Motivation = seeds for super-massive black holes formation Early formed black holes : Remnant of first stars formation at z 20 M 10 2 M Collapse of primordial gas M 10 5 M DM spike formation & Tidal destruction during merging Cosmological simulations are used to determine IMBHs properties Number of unmerged black holes Spatial distribution DM spike parameters P. Brun TeV Particle Astrophysics II at University of Wisconsin 17
Relevant Properties of IMBHs Expected number of IMBHs in the Milky Way : 98 ± 20 Radial distribution : Dark matter mini-spike : r s 1pc Source boost factor distribution : P. Brun TeV Particle Astrophysics II at University of Wisconsin 18
Neutral Particles from IMBHs IMBHs could provide strong evidence for Dark Matter in γ and ν s Spots off the galactic plane, no X-ray counterparts large field of view γ experiments neutrino telescopes EGRET AMS GLAST G. Bertone, A. Zentner & J. Silk (2005) P. Brun TeV Particle Astrophysics II at University of Wisconsin 19
Effective boost factor with IMBHs Monte Carlo simulations and analytical expectations for scenario B : Boosts of O(10 3 ), High variance P. Brun TeV Particle Astrophysics II at University of Wisconsin 20
Different Statistical Regimes Boost at 1 GeV : large V s, relatively low variance Boost at 50 GeV : small V s, high variance 1 IMBH 2 IMBHs P. Brun TeV Particle Astrophysics II at University of Wisconsin 21
Some Results for Antiprotons No Energy dependence : from the e + case Variance energy dependence have an opposite behavior : Interactions in the disk switched off : With interactions in the disk : Preliminary Preliminary P. Brun TeV Particle Astrophysics II at University of Wisconsin 22
Summary Boost factors : Are energy dependent Depend on the type of particle Predictions relie on statistical studies Realistic scenarios : B e + 20 for clumps B e + 2000 for IMBHs B p 3000 for IMBHs (if we are lucky!!!) Will be implemented in next version of micromegas P. Brun TeV Particle Astrophysics II at University of Wisconsin 23