Reionizing the Universe with Dark Matter :

constraints on self-annihilation cross sections

Fabio IoccoMarie Curie fellow at

Institut d’Astrophysique de Paris

IDM 2010Montpellier, 27/07/10

Indirect local DM searches

Courtesy of P. Salati

, ‘ s: straight messengers

e+, p, e- …subject to magnetic fields,diffusion, energy losses

Astrophysical uncertainties: CR propagation, DM halo density profile, boost factor

( r ) = smooth + clumps

Indirect searches of annihilating DM

The SA DM signal (easily re-writable for decaying DM)

Which line of sight?

Particle physics astrophysics(structures)

with substructures <2> ≥ <>2

Constraining with multimessenger

[Pato et al. `09]

<v>=<v>e+

Via Lactea Aquarius

Courtesy of NASA (through Google, Wikipedia, etc etc etc.)

Going early Universe

DM annihilation and the IGM

e

p

W

primary HE shower

heating and ionization

Courtesy of T. Slatyer

GeV -TeV scale

keVscale

Smooth component

Structure component

Structure formation history(Press-Schechter / Sheth-Tormen)

DM density halo profile Burkert / Einasto / NFW

Only after structure formation z ≤ ≈ 100

Isotropically averaged cosmological DM annihilation(easily re-writable for decaying DM)

…and its absorption by the surrounding gas(coupling DM induced shower to IGM)

Photoionization, IC scattering, pair production (on CMB and matter),

scattering

[Slatyer et al. `09]

“Opacity window” of the Universe

Neutral:Ly- absorber

z

Ionized:Ly- free to pass by

z ~ 6

“Reionization”: a history of free electrons

Completely ionized IGM

= 0.084

= neutral gas

Electron optical depth

Integrated quantity

Known contribution

Sources z > 6: known unknowns

constraints(DM annihilations can overproduce free e-)

To be integrated!

[Cirelli, FI, Panci `09]

In this models:

no astrophysical sources (z > 6)

Extra-conservative bounds!

Transparency of the Universe& structure formation

HE shower gets efficiently absorbed

at high z

Structure formation takes place in a late Universe (z < 60)

[Slatyer et al.`09]

[Cirelli, FI, Panci `09]

Self-annihilating DM and the IGMThe smooth DM component

annihilates with a rate (per volume)(easily re-writable for decaying DM)

depositing energy in the gas (IGM) at a rate

Main effect ofinjected energy:

ionization of the IGM

fre

e e

lect

ron

fra

ctio

n, x

e

The only DM parameter is

[Galli, FI, Bertone, Melchiorri `09]

Self-annihilating DM and the CMB

DM annihilationcauses indirect effects,

SZ by “additional” e-[Galli, FI et al. `09]

Modifying TT, TE, EE withadditional e- (by DM annih)

@ z >1000 , many e- no effectsenergy injection is small

Constraining DM with CMB

[Galli, FI et al. `09]

Evaluating “ f ”

All channels,all secondaries,redshift dependence

[Slatyer et al. 09]

leptons quarks

XDM => e XDM =>

Branching ratio ofDM annihilation

essential fordetermining absorption

Constraining DM with CMB

Thermal WIMP

[Galli, FI et al. + Slatyer et al `09]

Constraining Sommerfeld Enh. with CMB

[Galli, FI et al. 09]

zr=1000, 10-8

Sommerfeld saturated

A toy-Yukawa potentialSommerfeld enhancement

f = 0.5

cold DM !!!!

Constraints on decaying DMSame principle, same physics,

different “time dependence” of energy injection

DM Cirelli, FI, Ibarra, Panci, Tran:

preliminary results!

Constraints are not so strong:if the particles decay today, they did

less decay in the past…

[Catena et al. `10]

Comparing constraints

Concluding

It is possible to use Early Universe astrophysical observables to constrain DM properties

Self-annihilating DM can inject enough energy (free electrons)to modify the cross correlation CMB spectra!

The detectability of a DM annihilation in the CMB signal is DM model dependent (annihilation channel)

Would you ever believe we have found DM if I told you there is an (even strong) anomaly in the TE CMB spectrum?

Signal comes from smooth, cold DM density field(can get rid of structure formation uncertainties!

And it rocks with SE)

Observing Reionization:electrons and CMB

z

Damping of spectra

low(er) l polarization signal

Temperature constraints!

[CIP 09]

“Exotic heating”:DM, after coupled f

1/3 heat, 1/3 ioniz. 1/3 Ly-

Pamela saga: the e+ excess

[Delahaye et al. `09]Evidence for e+ excess: primary positrons

Combining the constraints on self-annihilating

[Hurtzi et al 09]

channel NFW profile

[CIP 09]

gammas + + IGM temperature

Einasto

NFW

Burkert

ee

ee

ee

[CIP `09]

Galactic bounds and their uncertainties

Radio constraints from GC (B=10 mG) [Bertone et al. `09]

IC gamma constraints (from GC)[Cirelli & Panci `09]

<sv> ≤ 10-21cm3/s5.1x10-4 ≤ Z ≤ 2x106

[McDonald, Scherrer, Walker ‘02]

[Zavala, Volgersberger, White ‘09]

Looser constraint than from anisotropies

The equation to Solve-IEnergy deposition rate

Gas (IGM) Opacity

Annihilation rates

The equation to Solve-IIEvolution of ionization fraction

Recombination rates

Ionization rates

Watching negative: gammas

[Profumo & Jeltema 09]

Mainly IC photons

z band breakup:locally dominated

e+ e-

boost IC

The Pamela(/Fermi/ATIC) saga

IF intepreted as DM:

High annih cross-section<v> ~10-24-10-21cm3/s

Forget about thermal decoupling

WIMP miracle

Unless<v> = <v>(v)

DM decoupling: ~1

Recombination: ~10-8

Small halos: 10-4

Milky Way: ~10-4

By courtesy of M. Cirelli

“Sommerfeld” enhancementfulfills the requirements(higher masses preferred)

E [GeV]

e- + e+

e+ fraction

Electron optical depth

Measured with CMB polarization

WMAP 5 value

Integrated quantity!