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Celine Bœhm, Unesco 2005 Is Dark Matter light? Status and prospects of the Light Dark Matter scenario in view of the 511 keV line

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Status and prospects of the Light Dark Matter scenario in view of the 511 keV line. Is Dark Matter light?. Celine Bœhm, Unesco 2005. Confirmation of a 511 keV emission in the centre of the galaxy by INTEGRAL/SPI. e+. e + e - g g. e-. 33deg, 16deg FoV. - PowerPoint PPT Presentation

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Page 1: Celine Bœhm, Unesco 2005

Celine Bœhm, Unesco 2005

Is Dark Matter light?

Status and prospects of the Light Dark Matter scenario in view of the 511 keV line

Page 2: Celine Bœhm, Unesco 2005

Celine Bœhm, Unesco 2005

Confirmation of a 511 keV emission in the centre of the galaxy by INTEGRAL/SPI

E = me

Narrow line which is the sign of electron-positron annihilations at rest.

Para-positronium Ortho-positroniume-

e+

In flight annihilations

e+ e-

E < me E < Ee

33deg, 16deg FoV

Page 3: Celine Bœhm, Unesco 2005

Great improvement of the sensitivity which confirms the origin of the line and its characteristics

Balloon experiments(HEAO3)

Satellite experiments(OSSE, INTEGRAL)

Celine Bœhm, Unesco 2005

Page 4: Celine Bœhm, Unesco 2005

Comparison between past and new measurements :

OSSE:

INTEGRAL:

Celine Bœhm, Unesco 2005

Detection of 3 components:

•Bulge•Disc•PLE(Positive latitude Enhancement)

Detection of 1 component:

• Bulge• Disc but due to radioactivity• Bulge/Disc>0.4-0.8• No PLE

Page 5: Celine Bœhm, Unesco 2005

Celine Bœhm, Unesco 2005

Possible sources of positrons

Stars SNe (Co 56) SNII (Al26, Ti 44) WR (Al 26)

Compact sourcesPulsarsBlack holesLow Mass Binaries

Cosmic raysp-anti p -> positronsRadioactive isotopes

General problem (except for old populations/LMB):

Too low Bulge/Disc ratio

Page 6: Celine Bœhm, Unesco 2005

Possible source of low energy e+ in the GC

LMB, old stellar population, or other unknown sources

Not clear whether LMB could fit both the observed flux, the line width and the morphology of the emission, but …

Maybe new mechanisms are the answer but, in any case, an astrophysical explanation remains to be found

New physics (or astrophysics)

Easier in fact since the model already existed for other purposes!

Celine Bœhm, Unesco 2005

Page 7: Celine Bœhm, Unesco 2005

New physics at the origin of the emission(?)

1) DM annihilates into electon-positron

2) The positrons lose their energy through ionization

3) Once at rest, the positrons can annihilate with electrons of the medium and form para-positronium

4) The para-positronium states gives 511 keV photons

To avoid an overproduction of low energy gamma rays, the DM mass must be lower than 100 MeV

e-

e+

edm

dm

e-

e+

Celine Bœhm, Unesco 2005

e+ lose energy

(DM mass must be < the muon threshold, to avoid pion production)

Page 8: Celine Bœhm, Unesco 2005

Are Light Dark Matter particles (lighter than a proton) possible?

Scenario proposed before INTEGRAL

The aim was to show that it is possible to evade the Lee-Weinberg limit

I.e. DM particles can be lighter than a few GeV but the annihilation cross section nowadays must be reduced compare to its value in the past universe by 5 order of magnitude times mdm

2

But are their characteristics compatible with the morphology of the 511 keV emission in the galactic centre?

Nowadays:

Celine Bœhm, Unesco 2005

Page 9: Celine Bœhm, Unesco 2005

Celine Bœhm, Unesco 2005

First results from a model fitting analysis (modelling the source)

FWHM ~ 8.5deg

~ 10-3 ph/cm2/s

Width is less than 10 keV!

Page 10: Celine Bœhm, Unesco 2005

Naïve comparison with DM prediction!(Assuming a DM halo profile as ρ(r)≈ρ0/r)

Full Width Half Maximum (extension)

Flux: require cross section of 10-31 cm3/s

Full width

Half maximum

Celine Bœhm, Unesco 2005

Page 11: Celine Bœhm, Unesco 2005

J. Knodlseder et al, Lonjou et al, 2003

Celine Bœhm, Unesco 2005

Reconstruction

Needs to assume a model for the source, e.g. gaussian, ponctual, halo/bulge model or DM distribution

One ponctual source is excluded!

Page 12: Celine Bœhm, Unesco 2005

A better Analysis was needed

• Previous results compared the FWHM expected for DM with that obtained assuming a gaussian distribution.

• That is not what one should do.

• Instead one has to determine the characteristics that SPI would see if DM was indeed at the origin of the emission

• So INTEGRAL analysis must start from the positron distribution as produced by DM annihilations!

Celine Bœhm, Unesco 2005

Page 13: Celine Bœhm, Unesco 2005

Elements for starting a new analysis

Cross section depends on:1. The DM mass (mdm)2. The DM energy (Edm)3. The couplings4. (The mass of the particle that is exchanged)

DM non relativistic at annihilations. Thus, Edm= ½ mdm v2 + mdm c2

Therefore the cross section depends on constant terms and v2

A convenient decomposition is then given by:<σv> = a + b v2 where a and b are constants.

Celine Bœhm, Unesco 2005

Page 14: Celine Bœhm, Unesco 2005

New analysis based on SPI response and background • Testing the a-term and the b-term• 4 different models of the DM halo

About the same as the previous version of the model !!!

Celine Bœhm, Unesco 2005

Page 15: Celine Bœhm, Unesco 2005

Results/consequences for the model

Decaying DM is now excluded (unless perhaps…) An a-term is needed to fit the 511 keV emission but suppressed by 5 o.m So a b-term is needed for the relic density

As predicted initially:

with

Celine Bœhm, Unesco 2005

Contribution to b solely. Cannot explain the 511 keV line but is required for the relic density

Contribution to a AND b with a=b so this diagram MUST be suppressedBut fit the 511 keV line

Page 16: Celine Bœhm, Unesco 2005

Consequences for/Prospects in Particle Physics

No theory but a very successful model perhaps

But important checks to do:

Collider physics Neutrino physics (NuTeV) G-2

Celine Bœhm, Unesco 2005

Page 17: Celine Bœhm, Unesco 2005

Celine Bœhm, Unesco 2005

S. Davidson et al, C. Boehm 2004

NuTeV anomaly

Page 18: Celine Bœhm, Unesco 2005

The fine structure constant F particles contribution to g-2

Deviation from SM

Where does the anomaly come from?

1. ath = f(α)2. impose ath = aQED and found αth3. Compare it with the experimental measurement Quantum Hall effect

Using the LDM model as determined by the 511 keV line:

For mdm~6-7 MeV

(prediction also for the muon!)

Page 19: Celine Bœhm, Unesco 2005

Colliders

Scalar

Fermionic

Celine Bœhm, Unesco 2005

Page 20: Celine Bœhm, Unesco 2005

Conclusions

The 511 keV line characteristics are now extremely well determined

Light DM fits successfully the morphology of the emission while astrophysical explanations are still to found (but not excluded!)

If LDM is the correct explanation, then the profile of the Milky Way should be cuspy (a la NFW)

LDM has maybe already manifested in PP experiments (via g-2 experiments, --NuTeV??--). Needs more focus on these aspects now.

LDM should be a scalar rather than a fermion. It should annihilate (not decay).

Problem though: no theory (except perhaps N=2 SUSY) but so does Lambda in fact..

Celine Bœhm, Unesco 2005

Page 21: Celine Bœhm, Unesco 2005

If DM is a fermion and coupled to heavy particles (Z, W) then it should be heavier than a few GeV.

Lee-Weinberg:

How light DM can be ? (Particle Physics)

Boehm-Fayet:

If DM is a fermion and coupled to light particles then it can be lighter than a few GeV.

If DM is a scalar and coupled to light or heavy particles then it can be lighter than a few GeV.

Celine Bœhm, Unesco 2005

Page 22: Celine Bœhm, Unesco 2005

Celine Bœhm, Unesco 2005

Light scalars (Boehm&Fayet, 2003):

coupled to heavy particles (F): v-independent cross section

coupled to light particles (Z’): v-dependent cross section

Light fermions (Fayet 2004):

coupled to light particles (Z’): v-dependent cross section

Z’ are required to escape the Gamma ray constraints

22 2 2 2dm

dm U Ul Ur4U

m v v C (f + f )

m