Dark Matter Models

Stephen West

Fellow\Lecturer

RHUL and RAL

and

Introduction

‣ Research Interests‣ Important Experiments

Dark Matter - explaining PAMELA and ATIC‣ Some models to explain data‣ Freeze out‣ Sommerfeld effect

Summary

2

Outline

Research Interests

‣ BSM model building‣ Supersymmetry‣ Higgs Physics‣ Neutrino Physics‣ Flavour Physics‣ Extra Dimensions‣ Early Universe Cosmology

✴ Baryogenesis/Leptogenesis

✴ BBN

✴ Dark Matter

Dark matter

‣ At the LHC

‣ Astrophysics Experiments

Evidence for Dark matter:

4

Dark Matter

• Cosmological Scales: CMB power spectrum...WMAP

• Galactic Scales: Rotation Curves, expect velocity of stars v(r) ∝ 1/√r but measure flat rotation curves

• Galaxy Cluster Scales: Bullet cluster, other cluster dynamics

!h2dm = 0.1143± 0.0034!

‣ PAMELA ( )‣ ATIC ( )‣ Hess ( )‣ + many more‣ CDMS‣ Zeplin‣ DAMA‣ + many more

Current Data:

Future Data:

Indirect Detection

DirectDetection

}}

!

e±, p±

!!

‣ FERMI/GLAST ( )‣ Icecube ( )‣ LHC?...

e±, p±

5

Important Experiments

GCRs high-energy particles flowing into our solar system from far away in the Galaxy.

!

‣ Composition: protons

electronshelium

+ other heavier nuclei

! 90%! 9%

‣ Origins: ✴ Probably accelerated in the blast waves of supernova remnants (SNRs)

✴ Particles/Nuclei bouncing back and forth in magnetic field of the remnants

✴ Some gain enough energy to escape into Galaxy and become GCRs

Galactic Cosmic Rays(GCRs)

! 1%

6

‣ Some GCRs observed with energies above max possible energies produced by SNRs

More GCRs

‣ Origins? ✴ Sources outside the Galaxy

✴ Quasars/Pulsars

✴ Exotic new physics: E.G. Dark Matter...

Observed range 1! 1, 000, 000 GeV/n

compared to ESNRmax ! 10, 000 GeV/n

✴ gamma ray bursts

‣ Some cosmic rays are observed above expected rates...

7

Payload for Antimatter Matter Exploration and Light nuclei Astrophysics

PAMELA

8

neutrondetector

anti-coinci-dence

ma

gn

et

B

X

ZY

proton antiproton

scint. S4

calorimeter~16.3 X

~0.60

Il

trackingsystem

(6 planes)

geometricacceptance

CAT

CAS

CARD

spectrometer

TOF (S1)

TOF (S2)

TOF (S3)

‣ Satellite experiment launched in 2006

‣ Primary goal: measure antimatter component of cosmic rays.

‣ Able to identify positively and negatively charged particles

Payload for Antimatter Matter Exploration and Light nuclei Astrophysics

‣ Measure spectra of antiprotons and positrons

9

PAMELA

PAMELA Results:Anti-Proton fraction

PAMELA Collaboration (O. Adriani et al.), Phys.Rev.Lett.102:051101,2009.

kinetic energy (GeV)1 10

210

/pp

-410

-310

IMAX 1992

BESS 2000 HEAT-pbar 2000

CAPRICE 1998

CAPRICE 1994 BESS-polar 2004

MASS 1991

BESS 1995-97

BESS 1999

PAMELA

kinetic energy (GeV)1 10

210

/pp

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4-3

10!

=500MV) !Donato 2001 (D,

=500MV) !Simon 1998 (LBM,

=550MV) !Ptuskin 2006 (PD,

PAMELA

Energy (GeV)

1 10 100

))

-(e!

)+

+(e!

) / (

+(e!

Po

sit

ron

fra

cti

on

0.01

0.02

0.1

0.2

0.3

PAMELA

Energy (GeV)

0.1 1 10 100

))

-(e!

)+

+(e!

) / (

+(e!

Po

sit

ron

fra

cti

on

0.01

0.02

0.1

0.2

0.3

0.4

Muller & Tang 1987

MASS 1989

TS93

HEAT94+95

CAPRICE94

AMS98

HEAT00

Clem & Evenson 2007

PAMELA

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PAMELA Results:Positron fraction

PAMELA Collaboration (O. Adriani et al.), arXiv:0810.4995 [astro-ph]

Advanced Thin Ionization Calorimeter

‣ Balloon experiment collecting data in 2000, 2003 and 2007

‣ Cannot distinguish between and e+e!

‣ Measures total electronic flux ( )in energy range 20-2400 GeV

e! e++

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‣ Also detects protons and heavier nuclei

Striking Results...

ATIC

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ATIC resultsATIC Collaboration (J. Chang et al.), Nature 456:362-365,2008.

Expected energy dependence of background Excess corresponds to 70 out of 210 total

AMS (green stars)

HEAT (open black triangles)

Emulsion chambers (black open diamonds)

BETS (open blue circles)

PPB-BETS (blue crosses)

AMS and HEAT are satellite experimentsBETS and PPB-BETS are balloon experiments

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Explaining the rise...

‣ Nearby astrophysical objects e.g. Pulsars

‣ Dark Matter

arXiv:0804.0220 See e.g.arXiv:0812.4457arXiv:0810.1527 Hooper et al.

Büsching et al.

Profumo

Seems possible to explain PAMELA and ATIC with pulsars

✴ Annihilations✴ Decays ! ! 1026sDM

DM

SM

SMDM

SM

SM

Many refs for dark matter, see e.g. Ref list in

Profumo arXiv:0812.4457

Decaying dark matter

‣ Candidates:

Lifetime ! ! ! 1026s

Decays have restricted branching fractions:

BHAD < 0.1

✴ Gravitino

✴ “Hidden sector” particle

✴ Maybe others...✴ Composite particles

Several ideas along these lines in literature

Annihilating dark matter

1) Annihilations rates must be large to account for large PAMELA and ATIC signals need boosts

✴ A problem for standard thermal dark matter

2) Annihilations must not produce too many hadrons

✴ Annihilation products usually include both hadrons and lepton

3) Annihilations must not produce too many photons

✴ Strong limits exist on photon signals

✴ Photons produced at wide range of frequencies for charged decay products

problem for standard thermal dark matter

Particle in thermal eq. present abundance:

neq ! (m/T )3/2e!m/T

However, if species freezes out i.e. ! < H

at temp T such that m/T ! 25

Can have significant relic abundance today

!

Using Boltzmann equations we get

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1) Annihilations rates must be large-

Kolb & Turner, `90

!dmh2 ! O(10!27 " 10!28)#!v$ GeV !2

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But we know that !dmh2 = 0.1143± 0.0034

This is weak scale interaction with weak scale mass particle

! WIMPThis fixes !!v"

sets the size of annihilations of DM particles as a function of DM velocity

!

!! A way out !! Change how !!v" depends on velocity

!dmh2 ! O(10!27 " 10!28)#!v$ GeV !2

! "!v# = (10!26 $ 10!27)GeV !2

Normally

The Sommerfeld Effect

‣ Heavy DM moving at small (relative) velocity

‣ Exchange of scalar (or vector) state

enhancement in annihilation cross section

(Sommerfeld; Hisano et al, Strumia et al...)

‣Corresponds to summation of

diagrams Only significant for s-wave

! (AM barrier)

!v = a + bv2

!

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!v ! 1vr

DM

DM

March-Russell, West, Cumberbatch, Hooper.

The Sommerfeld Effect‣ Calculation formed in terms on non-rel two body

QM problem with a potential

‣ Equivalent to distorted Born-wave approximation common in nuclear physics.

‣ Including the effect (to a good approximation)

! = R!l=0tree

‣ Full calculation of R can be involved

‣ For a Yukawa potential R cannot be solved analytically

‣ Can be enhancement or suppression for vector exchange

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Calculating R

‣ Scalar “rungs on the ladder”states can be then

‣ The Schrödinger equation for two DM particle state

‣ Enhancement factor R = |!(0)/!(!)|2

‣ Outgoing B.C

21

! 1mdm

d2!

dr2+ V ! = K! K = mdmv2V = ! !2

8"re!mn

‣ Introduce the following term!

2n"dm"dm

! ! !dm!dm

!!(!)/!(!) = imdmv

Coulomb limit‣ Analytic form for R in limit

‣ Small limit

What about ?! != 0

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y = !2/4vR =y

1! e!y

v

R ! !2

4v

! ! mn/mdm = 0

!1 0 1 2 3 4 5 6

0.0

0.5

1.0

1.5

2.0

Log!""##

Log!""$#

Contours in R

! ! 0.2

3 10 30 1003001000

Enhancement for ! != 0

Freeze out

!! FO

FO

!/" > 1!/" > 1

Need

Indirect detection

! ! 10!3 " 10!5

!ID

ID ID23

! ! mn/mdm

! = "2/8#

! ! 2

0

2

4

6

0.0

0.5

1.0

1.5

0

500

1000

3D Version

R

Log[!/"]

Log[!/"]

500

1000

0

0

0.5

1.51.0

2

4

6

24

March-Russell, West.

1) Annihilations rates must be large -Alternatives

‣ Could consider non-thermal dark matter

✴ Late decaying particles

✴ Another interesting idea later

‣ Over densities - No. annihilation

✴ Regions of high density

✴ Near Black Holes?

✴ Naturally occurring clumps?

! !2dm

2) Annihilations must not produce too many hadrons

‣ Leptophilic models

✴ Need to introduce extra quantum numbers

✴ Can introduce two dark matter states and have inelastic scattering

‣ Kinematic tricks and extra symmetries

✴ dark matter only talks to leptons due to symmetries

DM

DM

!µ, e

µ, e

! possible to reconcile DAMA with other direct detection experiments

✴ Particle can generate Sommerfeld enhancement

!

(Arkani-Hamed et al...)

Fox, Poppitz, arXiv:0811.0399

3) Annihilations must not produce too many photons

‣ All annihilations with charged states can produce photons

✴ Boosting annihilation rates into means we produce more photons

e±

✴ Measurements of Cosmic diffuse background radiation tightly constrain scenarios

Summry‣ PAMELA and ATIC inspired a lot of model building

‣ If DM is the answer, need large boosts to annihilation cross sections

‣ Several ways to generate boost factors but all have restrictions and constraints

‣ PAMELA and ATIC data have inspired a lot of unusual and compelling new ideas - many more to come...

‣ Maybe explained by astrophysics

✴ Exciting times ahead