dark matter and dark energy components chapter 7cdeclerc/astroparticles/2012-13/dark-matter-d… ·...

Dark Matter and Dark Energy components

chapter 7

Lecture 4

See also Dark Matter awareness week December 2010

http://www.sissa.it/ap/dmg/index.html

The early universe chapters 5 to 8

Particle Astrophysics , D. Perkins, 2nd edition, Oxford

5. The expanding universe 6. Nucleosynthesis and baryogenesis 7. Dark matter and dark energy components 8. Development of structure in early universe

Slides + book http://w3.iihe.ac.be/~cdeclerc/astroparticles

Overview

• Part 1: Observation of dark matter as gravitational effects – Rotation curves galaxies, mass/light ratios in galaxies

– Velocities of galaxies in clusters

– Gravitational lensing

– Bullet cluster

• Part 2: Nature of the dark matter : – Baryons and MACHO’s

– Standard neutrinos

– Axions

• Part 3: Weakly Interacting Massive Particles (WIMPs)

• Part 4: Experimental WIMP searches

• Part 5: Dark energy

2012-13 Dark Matter - Dark Energy 3

Previously – ΛCDM model

• Universe is flat k=0

• Dynamics given by Friedman equation

• Size of universe at given time

and today , t0

• Closure parameter relates density to critical density • Energy density evolves with time, and so does H


2

2 8

3

NR t G

R ttH t totρ

0

01 0R t

z z tR t

c

tt

t

2 3 4 22

0 0 01 1 1r kH t H z t z t z0 0m ΛΩ t Ω t

Ωk=0

tot mat rad

Energy budget of universe today


luminous 1%

dark baryonic

4%

Neutrino HDM <1% cold dark

matter 18%

dark energy

76%

• Today only 5% of the matter-energy consists of known particles

• 18% is Cold Dark Matter = new type of particles

• 76% is completely unknown 510

0.24

rad

matter

2 3 42

0 0 0 01 1m rH t H t z t z t

Previous lecture : Dark Matter

• Observation of dark matter as gravitational effects

• Nature of dark matter particles is still inknown

– Baryons

– MACHOs = Massive Compact Halo Objects

– Neutrinos

– Axions

– WIMPs = Weakly Interacting Massive Particles

• Identifying dark matter : direct and indirect detection experiments


Ωm

Where should we look?

• Search for WIMPs in the Milky Way halo

Indirect detection: expect WIMPs from the halo to annihilate with each other to known particles

Direct detection: expect WIMPs from the halo to interact in a detector on Earth


Dark matter halo

Luminous disk

Solar system

© ESO

PART 4: WIMP DETECTION

Identify the nature of dark matter with experiments


DIRECT DETECTION EXPERIMENTS


Principle of direct detection

• Earth moves in WIMP ‘wind’ from halo

• Elastic collision of WIMP with nucleus in detector

• recoil energy

• Velocity of WIMPs ~ velocity of galactic objects


N N

2

Rec 1 cos 50N

E keVm

2v µ

N

N

m m

m mµ

1 3~ 270 ~ 10km s cχv

Cross section and event rates

• Event rate depends on density of WIMPs in solar system

• Rate depends on scattering cross section – present upper limit


Rm

N χpσ

3~ 0.3GeV cm

DM

Den

sity

(G

eV c

m-3

)

Distance from centre (kpc)

Rate depends on number N of nuclei in target

44 2 810 10cm pbσ χp Weak interactions!

• low rate

large detector

• very small signal

low threshold

• large background :

protect against cosmic rays, radioactivity, …


Direct detection challenges

pRM

N

Annual modulation

• Annual modulations due to movement of solar system in galactic WIMP halo – 30% effect

• Observed by DAMA/LIBRA – not confirmed by other experiments


pRM

N

1~ 270v km s

Against the wind in June higher rate

In direction of the wind in December Lower rate

From event rate to cross section


R NM

χpσ

Other experiments see no signal and put upper limits on the cross section

Some experiments claim to see a signal at this mass and with this cross section

Expected cross sections for models with supersymmetry

INDIRECT DETECTION EXPERIMENTS


Indirect detection of WIMPs • Search for signals of annihilation of WIMPs in the Milky Way halo

• accumulation near galactic centre or in heavy objects like the Sun or Earth due to gravitational attraction

• Detect the produced antiparticles, gamma rays, neutrinos


, , ,..

, ,

qq

ll e

W Z H

neutrinos from WIMP annihilations : IceCube

• Neutrinos from WIMP annihilations in the Sun

• Neutrinos from WIMP annihilations in galactic halo, galactic centre, dwarf spheroidal galaxies

• Neutrinos from WIMP annihilations in the centre of the Earth

2012-13 17 Dark Matter - Dark Energy

WIMPs accumulated in the Sun


Detector

μ

ν interaction

, ,...qq ll

1. WIMPs are captured 3 2SUNC

v m

χNσ

2. WIMPs annihilate

1

2ANN SUNC

Capture rate

Annihilation rate

19

Search for GeV-TeV neutrinos from Sun

A few 100’000 atmospheric neutrinos per year from northern hemisphere

Max. a few neutrinos per year from WIMPs in the Sun

signal

~1011 atmospheric muons per year from southern hemisphere

BG

BG

2012-13 Dark Matter - Dark Energy

No excess above known backgrdound


Data Background

• No significant signal found

• Rate is compatible with atmospheric background

• Set upper limit on possible neutrino flux and annihilation rate

ψ(deg)

Nu

mb

er o

f ev

ents

Sign

al?

Combining direct and IceCube searches


IceCube

W W

2

SD p cm

A selection of SuperSymmetry models

~ ~Ann SUNC χNσ

Overview

• Part 1: Observation of dark matter as gravitational effects

– Rotation curves galaxies, mass/light ratios in galaxies



– Bullet cluster

• Part 2: Nature of the dark matter :

– Baryons and MACHO’s


– Axions





Part 5: Dark Energy

Observations

The nature of Dark Energy ΩΛ

Energy budget of universe today


luminous 1%

dark baryonic

4%

Neutrino HDM <1% cold dark

matter 18%

dark energy

76%

• Today only 5% of the matter-energy consists of known particles

• 18% is Cold Dark Matter = new type of particles

• 76% is completely unknown 510

0.24

rad

matter

2 3 42

0 0 0 01 1m rH t H t z t z t

OBSERVATIONS

SNIa surveys

Link to cosmological parameters



Nobel Prize in Physics 2011

SNIa as standard candles (see lecture 1)

• Supernovae Ia are very bright - very distant SN can be observed

• All have roughly the same luminosity curve which allows to extract the absolute magnitude M

• → effective magnitudes yield luminosity distance

• Network of telescopes united in

– Supernova Cosmology Project SCP, (Perlmutter) up to z=1.4 – have now data from 500 SN (http://supernova.lbl.gov/)

– High-z SN search HZSNS (Schmidt & Riess, in 1990’s) 2012-13 Dark Matter - Dark Energy 27

10

2.5log

5log 251Mpc

M L cst

z M LD

m

Luminosity distance vs redshift - 1

• SN at redshift z emits light at time tE – is observed at time t0

• Light observed today travelled during time (t0 - tE )

• distance travelled depends on history of expansion

• Proper distance DH from SN to Earth (lecture 1, horizon

distance)

• For flat universe (k=0) with negligible radiation content


32 2 2

0 0 0( ) 1mH z H t H t z t

0

0

EE

t

t

dct R t

R t

tHD

1

dz

zd

Ht

Luminosity distance vs redshift - 2

• Luminosity distance


300 00 0

12

1

z z

m

cdz c dz

Ht z t

HH z

D z

1 z HD zLD z

Luminosity distance DL vs redshift z

• Neglect radiation at low z – different examples


normalise to empty universe

• normalise measurements to empty universe

• Deceleration parameter is zero – universe is ‘coasting’


0 0 01, 0, 0k mt t t

2

2

R R Rq t

R R R

R

02

mr

tq t t t

20 00

12

1 12

1

z

L

c dz c zD empty z z

H Hz

R = 0

Hubble plot with high z SNIa


Empty universe: Ωm= Ωr=0 Ωk=1 No acceleration no deceleration

Vacuum dominated & flat

Matter dominated & flat

Log

DL

(Mp

c)

Redshift Z past now

Influence of cosmological parameters

• best fit

• Empty universe


Difference between measured logDL vs z and expected logDL vs z for empty universe

best fit

Empty universe

measurements

Measurements up to z=1.7

• Best fit


0 00.27 0.73m t t

log logL LD measured D empty

…. empty --- Best fit

Δ(m

-M)=Δ

DL

z

q(t)<0 acceleration q(t)>0 deceleration

past present

SN observations show acceleration

• Early universe : universe dominated by matter decelerates due to gravitational collapse :

• Recently : universe dominated by vacuum energy accelerates

• Acceleration = zero around z=0.5 when

• → Switch from deceleration (matter dominated) to acceleration (dark energy dominated)


2

mr

tq t t t

0 0mq t t R

0 0q t t R

2

mr

tt t

THE NATURE OF DARK ENERGY

Related to cosmological constant ?

problems


Dark vacuum Energy

• Observed present-day acceleration means that Dark Energy generates a negative pressure

• Yields gravitational repulsion like vacuum energy

• Equation of state (see lecture 1)

• Fits to SNIa data yield that w is compatible with vacuum energy


2

vac

S

EP c cst

V2

Pw

c

0.85 at 95% . .w C L

Related to cosmological constant Λ

• In ΛCDM – ΩΛ is constant and related to Einsteins cosmological constant

• If Universe contains constant vacuum energy density related to Λ then we set

• In very early Universe there was only vacuum energy

• At Planck energy scale gravity becomes strong

• energy and length scales

• And expected energy density


8 vacG

15 2

2 191.2 10def

PL

cM c GeV

G

351.6 10DEF

PL

PL

L mM c

22 123 3

exp 310PL

vac

PL

M cc GeV m

L

Cosmological constant problem

• Today vacuum energy density is of order of critical density

• Discrepancy of 100 orders of magnitude !!!

• Did vacuum energy evolve with time?

• There is no explanation yet

• need high statistics data :

– Dark Energy Survey – start 2011 (http://www.darkenergysurvey.org/)

– WFIRST mission of NASA – launch 2020 (http://wfirst.gsfc.nasa.gov/ )

– ESA EUCLID mission – launch 2015-20 (http://www.esa.int )


2 2 30.76 5vac critobs

c c GeV m 2 123 3

exp10vacc GeV m

http://www.darkenergysurvey.org/

http://www.darkenergysurvey.org/

http://wfirst.gsfc.nasa.gov/

http://www.esa.int/

Alternatives

• Quintessence – 5th force : acceleration is due to potential energy of a dynamical field

• Vacuum energy density varies with time

• Mechanism analogue to inflation

in early universe

• Maybe general relativity works differently at large distances


2

Pw t

c

113

w t

Summary

• Observations of SNIa emission show that the universe presently accelerates

• This can be explained by a constant dark vacuum energy contribution which dominates today

• In the ΛCDM model the dark energy is related to the cosmological constant introduced by Einstein

• There is yet no satisfactory explanation for the observed magnitude of the dark energy


Overview

• Part 1: Observation of dark matter as gravitational effects – Rotation curves galaxies, mass/light ratios in galaxies



– Bullet cluster

• Part 2: Nature of the dark matter : – Baryons and MACHO’s


– Axions





dark matter and dark energy components chapter 7cdeclerc/astroparticles/2012-13/dark-matter-d… ·...

Documents