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B.Sadoulet
Phys 250 -1 1
The Dark Side
The Dark Side of the Universe
LogisticsAn overview
A first taste without the sourness of equations!
Outline
B.Sadoulet
Phys 250 -1 2
The Dark Side
LogisticsBasic Information
Instructor: Professor Bernard Sadoulet ([email protected])Class Time: T/Th 9:40-11:00 Pacific TimeClass Location: 501 Campbell Hall UCB and on the InternetOffice Hours:
Immediately after class in 501 Campbell (Astronomy Dept Coffee)Thursday 2:00-3:00 301 LeConte or by phone (510 642 5719)Or by appointment
Credit (UCB)Requirements
regularly attend the lectures and read the assigned preparatory material problem sets approximately every three weeks a final paper on a topical aspect of the dark matter or dark energy problems
Outline due end of OctoberPaper due Dec 1
Other students and postdocs are welcomed (and encouraged) to submit problem setsand the final paper.
Should only represent medium load!
Books:None required (we will use recent articles on the web)P.J.E. Peebles “Principles of Physical Cosmology” (Princeton University Press, 1993)E.W. Kolb and M.S. Turner “The Early Universe” (Addison-Wesley, 1994)
B.Sadoulet
Phys 250 -1 3
The Dark Side
Style
As interactive as possibleYour own experienceLinkages and connections
Attempt to go beyondThe standard lore and current fashionThe maths or the complexity
Spirit of Awe
Looking beyond: Camille Flammarion
B.Sadoulet
Phys 250 -1 4
The Dark Side
Initial explosion!<= Expansion of the universe
Since Hubble (1925) we know that distant galaxiesare receding from each other
<= Universe was hot in the early timesWe detect the glow in cosmic microwave background
Initially at 3000K, now at 2.73K
The formation of deuterium, helium and lithium requires a hot furnace
The Big Bang
B.Sadoulet
Phys 250 -1 5
The Dark Side
Galaxies as Tracers ofSpace
Hubble Space TelescopeDeep Field
≈ 5 million galaxies/squared degree200 billion galaxies over whole sky
B.Sadoulet
Phys 250 -1 7
The Dark Side
Primordial Nucleosynthesis
Not enough 4He producedto account for observed≈23% in mass
=> hot early universe(Gamov)
B.Sadoulet
Phys 250 -1 8
The Dark Side
From Quarks to the Cosmos
Big Bang enables influence of infinitely small oninfinitely large
B.Sadoulet
Phys 250 -1 9
The Dark Side
The Role of Gravity
Expansion is governed by gravitySlowed down by gravity
At least we thought so, till recently!
Define critical density ρc as the density at which the kineticenergy and potential energy are equal in magnitude
> 1 recollapses = closed universe= 1 expands forever, stops at infinity = flat universe< 1 expands forever = open universe
Ω < 1
Ω = 1
Ω > 1time
a(t) = scale parameter (e.g.,distance between two distant galaxies)
=c
How can we have gravitational repulsion?Generalization of Newton’s law to General Relativity
If pressure is negative, gravity can become repulsive!
aacceleration
=G
r2
mass density V → a
acceleration =
G
r 2
1
c2 uenergy density
+ 3 ppressure
GR gravitational mass1 2 4 4 4 3 4 4 4
Vr
a
V
B.Sadoulet
Phys 250 -1 10
The Dark Side
Cosmic MicrowaveBackground
Boomerang + Maxima: The universe is spatially flat!
B.Sadoulet
Phys 250 -1 11
The Dark Side
The Role of Gravity 2Formation of structure
Gravity is unstable!Local increase of density tends to grow:
attracts matter around it.This generates velocities on top of expansion.
We see these fluctuations in cosmic microwavebackground.
We can follow them as a function of timeA quantum origin?
=> We need to do a little bit of General RelativityTo describe expansion
Understand how we can extract both the energy density and the pressure
To understand the growth of structureVery sensitive also to the energy density and the pressureAlso a signature of the nature of dark matter
Extrapolationflat universe
at z≈1000
CDM
ν onlybaryonic
Large scalestructureCMB
B.Sadoulet
Phys 250 -1 12
The Dark Side
The Initial Seeds
Seen in Cosmic Microwave Backgrounde.g. Boomerang
B.Sadoulet
Phys 250 -1 13
The Dark Side
A Bizarre Universe
Not a mixture of matter and antimatter!The most obvious guess: equal mixture of matter and antimatterWe do not see the high energy photons from matter-antimatter annihilation
There is more than ordinary matter and photonsOrdinary matter = baryons + electrons
Primordial abundance of deuterium => Ωbaryon≈ 5%
In addition:Dark matter
Represents ≈85% of “matter” = “which clumps!” => Ωdark matter≈ 30%Dominates gravity and is responsible for the formation of structure
Dark energy ?Evidence for acceleration of the universe = “antigravity!”Diffuse and appeared “recently” => Ωdark energy≈ 65%
Cosmic microwave background: universe is flat => SUM ≈ 100%
The
Dar
k Si
de !
B.Sadoulet
Phys 250 -1 14
The Dark Side
Dark Matter
Solid evidence that 85% ofthe mass in the universe isdark
rotation curves in spiral galaxies
globular clusters / gas aroundelliptical galaxies
velocity dispersion in clustersX-ray gas in clustersgravitational lensing by clusters
Large scale flows
B.Sadoulet
Phys 250 -1 15
The Dark Side
What is the Nature of Dark Matter
A map of the territory
=> systematic effort
non baryonic
exotic particles
non-thermal
Axions Wimpzillas
baryonic
gas VMO
dust MACHOs
clumped H2?
Mirror branesEnergy in the bulk
PrimordialBlack Holes
?
thermal
Light Neutrinos WIMPs
dark matter
B.Sadoulet
Phys 250 -1 17
The Dark Side
Non Baryonic Dark Matter
Many hints that the bulk of Dark Matter is non baryonic!
CandidatesLight massive neutrinosAxionsWeakly Interactive Massive Particles
Ωeff
Ho=65km/s/Mpc
0.001
0.01
0.1
1
10 100 1000 1e+04 1e+05 1e+06
Vel Corr.b=1
Shaya et al.
Voids
BaryonInvent.
Cluster Evol.
Potentb=1
Power spectrum
Dipoleb=1
Supernovae+ CMBR
CosmologicalTests
Primordial Nucleosynthesis
Tytler et al.
Scale (kpc)
B.Sadoulet
Phys 250 -1 18
The Dark Side
CDMS I
View down tunnel (Icebox at far end) Icebox inside Pb shielding
Detectors
Inner Pb shieldPolyethylene
Pb ShieldActive Veto
20mK
B.Sadoulet
Phys 250 -1 19
The Dark Side
Recent Controversy
DAMA claims tohave foundWIMPs
CDMS hascontradictoryresults
B.Sadoulet
Phys 250 -1 20
The Dark Side
The Dark Energy Revolution
Supernovae at high redshift
Before After Subtraction
A HST image
B.Sadoulet
Phys 250 -1 21
The Dark Side
Dark Energy
One type of supernovaeappears to have veryconstant light curves
(once corrected for decay time)
Distant supernovae appeardimmer than expected ina flat universe
Potential problemsAre supernova properties really
constant?Dust?
Thursday 8/31: discussedby Saul Perlmutter
time
Lum
inos
ity
Distance
m=1=0
Fai
nter
B.Sadoulet
Phys 250 -1 22
The Dark Side
Very surprising!
What can it be?• Vacuum energy <- fluctuation p =-u Einstein’s gravitational
constantRelated to the zero point energy of harmonic oscillator
Naïve calculation: too small by 10120!
• A new form of matter/energy: Quintessence p =wu w >-1
• Tangled topological defects
=> We have no clue!
Why now?Evolution rate depends on w!
u t( ) ≡ t( ) ∝ a t( )−3 1+ w( )
B.Sadoulet
Phys 250 -1 24
The Dark Side
Our territory
Why b m
Do we understand Gravity?
nonbaryonic
exotic particles
non-thermal
Axions Wimpzillas
baryonic
gas VMO
dust MACHOs
clumped H2?
Other dimensions?Primordial
Black Holes?
Quintessence
thermal
Light Neutrinos WIMPs
dark matter and energy
B.Sadoulet
Phys 250 -1 25
The Dark Side
Our ToolsInventoriesPattern and growth of structurePattern and growth of velocitiesMeasurement of pressure
Because
we can measure both the energy density and the pressure by measuring theexpansion as a function of time or the distance vs z
Laboratory searchesDark matterDark energy
We will emphasizeNew probes
CMBR, supernovae, weak lensing, Sunyaev-Zel’dovich, laboratory detection
New toolslarge field of view telescopes, adaptive optics, large format arrays, cryogenic
detectors
accacceleration =
G
r2
1
c2 uenergy density
+ 3 ppressure
GR gravitational mass1 2 4 4 4 3 4 4 4
V
a t( )expansion ⇔ d z( ) ⇐ 1+ z =
a to( )a t( )
t = cd
B.Sadoulet
Phys 250 -1 27
The Dark Side
OutlineThe Current Paradigm
The Big Bang, Inflation and the homogeneity of the universe at large scale.General Relativity tools: Robertson Walker metric, Friedman equation.Spatial geometry and observations of the Cosmic Microwave BackgroundBaryon density: Baryogenesis and nucleosynthesis
Dark Matter: astrophysical observationsObservational evidence and inventoryThe pattern and growth of structure and velocitiesThe dark baryons: MACHOs and warm/hot diffuse baryons
Non Baryonic Dark Matter: the particle physics connectionEvidence for non baryonic natureTheoretical framework (QCD, supersymmetry, extra dimensions)Neutrino mass measurements Axion searches WIMP searches (Direct and indirect detection)
Dark Energy Observational evidence: high redshift supernovaeMeasuring pressure in the universe: distance versus redshiftWhat can be learnt from the growth of structure?Models for dark energy
Directions for progress