Upload
rolf-ford
View
218
Download
2
Embed Size (px)
Citation preview
The early universechapters 5 to 8
Particle Astrophysics , D. Perkins, 2nd edition, Oxford
5. The expanding universe6. Nucleosynthesis and baryogenesis7. Dark matter and dark energy components8. Development of structure in early universe
Slides + book http://w3.iihe.ac.be/~cdeclerc/astroparticles
Dark Matter - Dark Energy lect 4 3
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: direct & indirect
detection• Part 5: Dark energy2014-15
Dark Matter - Dark Energy lect 4 4
Energy budget of universe today
2014-15
luminous1%
dark baryonic4%
Neutrino HDM<1%
cold dark matter
25%
dark energy
70%
• Today only 5% of the matter-energy consists of known particles
• 25% is Cold Dark Matter = new type of particles
• 70% is completely unknown 510
0.30rad
matter
2 3 420 0 0 01 1m rH t H t z t z t
Planck, 2013
Dark Matter - Dark Energy lect 4 5
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
2014-15
Dark matter halo
Luminous disk
Solar system
© ESO
Weakly Interacting
Massive Particles
Dark Matter - Dark Energy lect 4
three complementary roads
6
, , , ,γν,f f W W e
Indirect search experimentsdi
rect
sea
rch
expe
rimen
ts
Production at the LHC collider
p p
Model
2014-15
Dark Matter - Dark Energy lect 4 7
PART 4: WIMP DETECTIONIdentify the nature of dark matter with experiment
2014-15
Dark Matter - Dark Energy lect 4 10
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
2014-15
WIMP WIM
Pe +, γ, υ, p
, , ,..
, ,
ll e
W Z H
Dark Matter - Dark Energy lect 4 11
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
2014-15
Dark Matter - Dark Energy lect 4 12
WIMPs accumulated in the Sun
2014-15
c
Detector
nμ
m
ν interaction
, ,...qq ll
1. WIMPs are captured 3 2SUNC
v m χNσ
2. WIMPs annihilate
1
2ANN SUNC
Capture rate
Annihilation rate
Dark Matter - Dark Energy lect 4 13
Search for GeV-TeV neutrinos from Sun
A few 100’000 atmospheric neutrinos per year from northern hemisphere
Max. a few 100 neutrinos per year from WIMPsin the Sun
signal
~1011 atmospheric muons per year from southern hemisphere
BG
BG
2014-15
Dark Matter - Dark Energy lect 4 14
No excess above known background
2014-15
DataBackground
• No significant signal found• Rate is compatible with
atmospheric background• Set upper limit on possible
neutrino flux and annihilation rate
ψ(deg)
Num
ber o
f eve
nts
Sign
al?
m
νμ
Dark Matter - Dark Energy lect 4 15
Combining direct and IceCube searches
2014-15
IceCube
W W
2SD p cm
A selection of SuperSymmetry models
~ ~Ann SUNC χNσ
Physical review letters 2013
Dark Matter - Dark Energy lect 4 16
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
2014-15
Dark Matter - Dark Energy lect 4 19
Energy budget of universe today
2014-15
luminous1%
dark baryonic4%
Neutrino HDM<1%
cold dark matter
25%
dark energy
70%
• Today only 5% of the matter-energy consists of known particles
• 25% is Cold Dark Matter = new type of particles
• 70% is completely unknown 510
0.30rad
matter
2 3 420 0 0 01 1m rH t H t z t z t
Dark Matter - Dark Energy lect 4 20
OBSERVATIONS
SNIa surveysLink to cosmological parameters
2014-15
Dark Matter - Dark Energy lect 4 22
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)
2014-15
10
2.5log
5log 251Mpc
M L cst
z M
LDm
Dark Matter - Dark Energy lect 4 23
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, part 2)
• For flat universe (k=0) with negligible radiation content
2014-15
00
EE
t
t
dct R t
R t
t HD 1
dz
zd
Ht
Dark Matter - Dark Energy lect 4 24
Luminosity distance vs redshift - 2
• Luminosity distance
2014-15
300 00 0
121
z z
m
cdz c dz
Ht z t
H H zD z
1 z HD zLD z
Luminosity distance DL vs redshift z
• Neglect radiation at low z – different examples
2014-15 Dark Matter - Dark Energy lect 4 25
Dark Matter - Dark Energy lect 4 26
normalise to empty universe
• normalise measurements to empty universe
• Deceleration parameter is zero – universe is ‘coasting’
2014-15
0 0 01, 0, 0k mt t t
02m
rt
q t t t
20 00
12
1 12
1
z
L
c dz c zD empty z z
H Hz
Hubble plot with high z SNIa
2014-15 Dark Matter - Dark Energy lect 4 27
Empty universe: Ωm= Ωr=0 Ωk=1No accelerationno deceleration
Vacuum dominated & flat
Matter dominated& flat
Log
DL (
Mpc
)
Redshift Zpast
Far a
way &
dimmer
now
Influence of cosmological parameters• best fit
• Empty universe
2014-15 Dark Matter - Dark Energy lect 4 28
Difference between measured logDL vs z and expected logDL vs z for empty universe
best fit
Empty universe
measurements
Dark Matter - Dark Energy lect 4 29
Measurements up to z=1.7
• Best fit
2014-15
0 00.27 0.73m t t
log logL LD measured D empty
…. empty--- Best fit
Δ(m
-M)=
ΔD
L
z
q(t)<0 acceleration q(t)>0 deceleration
pastpresent
http://supernova.lbl.gov
Dark Matter - Dark Energy lect 4 30
SN observations show acceleration
• Earlier 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)
2014-15
2m
rt
q t t t
2m
rt
t t
Dark Matter - Dark Energy lect 4 31
Fit ΛCDM model to observations
2014-15
m
pdg.lbl.gov
SN Ia distance-redshift surveys
CMB anisitropies survey by WMAP
Anisotropies in galaxy surveys
Dark Matter - Dark Energy lect 4 32
THE NATURE OF DARK ENERGY
Related to cosmological constant ?problems
2014-15
Dark Matter - Dark Energy lect 4 33
Dark vacuum Energy
• Observed present-day acceleration means that something = 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
2014-15
2vac
S
EP c cst
V
2
Pw
c
0.85 at 95% . .w C L
Dark Matter - Dark Energy lect 4 34
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
• A natural value would be the energy density at the Planck energy scale - energy and length scales
• And expected energy density
• Quantum field theory yields same value
2014-15
8 vacG
15 2
2 191.2 10def
PL
cM c GeV
G
351.6 10DEF
PLPL
L mM c
Dark Matter - Dark Energy lect 4 35
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 )
2014-15
Dark Matter - Dark Energy lect 4 362014-15
3 11
wz
© J. Frieman1 0.2DarkEnergyw
Is wDE constant with time?
Dark Matter - Dark Energy lect 4 37
Alternatives
• Quintessence – 5th force : new type of scalar field• Mechanism analogue to inflation in early universe• Vacuum energy density would vary with time
• Maybe general relativity works differently at short distances
2014-15
2
Pw t
c 11 3w t
Dark Matter - Dark Energy lect 4 38
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
2014-15
Dark Matter - Dark Energy lect 4 39
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 energy2014-15