things big & small

THINGS BIG & THINGS BIG & SMALLSMALL

Dhiman Chakraborty

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Dhiman Chakraborty THINGS BIG AND SMALL 2

Outline: Part 2 Outline: Part 2 • Up to the grandest: the Universe at large• Big Bang Cosmology: a brief overview

– The three tests of BB cosmology• Cosmic Microwave Background (CMB) Flat Universe• Large Scale Structure (LSS) Dark matter• Expansion of the Universe: Supernova 1a (SN1a) Dark E

– Recent/current/proposed experimental programs using ground- and space-based telescopes:

• CMB: COBE, WMAP, Planck• LSS: HST, SDSS, LSST, Chandra, XMM-Newton, …• SN1a: HZSNT, SCP, SNAP

• Summary of planned HEP & cosmology projects

• Outlook


Up to the Up to the grandest…grandest…


Big Bang Big Bang cosmology cosmology • t=0: the beginning of time & space represents an essential singularity with infinite matter-energy density () and temperature (T).

• An expansion ensues, governed primarily by GTR.

• T & fall as the universe expands.


Epochs & dominant Epochs & dominant componentscomponents• ? : <10-43 s; string (?)

• Inflation: 10-38 s; vacuum (inflaton driven?)– Quantum fluctuations imprinted on metric, to be seen later as

anisotropies in cosmic microwave background.

• Baryogenesis: 10-36 s; radiation/matter(?)– WIMP decoupling

• Big Bang Nucleosynthesis (BBN): 1 s; radiation

– neutrino decoupling. Best tested part, nB/n only parameter.

• Cosmic Microwave Background (CMB): 1012 s; matter– photon decoupling transition to matter-dominated era.

• Present: 51017 s; vacuum– “Dark energy” drives the universe into accelerated expansion.


Evolution of the Evolution of the UniverseUniverse


Evolution of the Evolution of the Universe Universe Time Since the Big Bang

The state of the Universe Human Equivalent

379,000 years

This is a time when the pattern of the Cosmic Microwave Background light was set. The Universe was just cool enough for atoms to form for the first time.

At this stage, the Universe is the equivalent of a baby just 19 hours old.

200 million years

The matter in the Universe condensed by gravity until the first stars ignited. WMAP has detected this event at about 200 million years after the Big Bang. (WMAP does not see the light of the first stars directly, but has detected a polarized signal that is the tell-tale signature of the energy released by the first stars.)

The Universe is the equivalent of a baby of 13 months, just old enough to begin taking its first steps.

1 billion years

The first galaxies began to form at about this time. Unlike a human child, the Universe has reached the end of its formative years at this young age. There are no further notable cosmic events past this stage.

At this age, the Universe is equivalent to a child just under six years old.

13.7 billion years

The present day Universe with its billions upon billions of stars and galaxies is found to be 13.7 billion years old, an age with a margin of error of close to 1 percent.

An adult person at 80.


Pillars of the Big Bang Pillars of the Big Bang theorytheory• Cosmic microwave background

• Abundance of the light elements

• Evidence of cosmic expansion

Observationally, these measurements

are completely independent of each

other. They must provide even support

for the theory to hold water.


Hubble’s lawHubble’s law Based on experimental observation (1929):On average, all galaxies are moving away

from each other with speed proportional to

distance.

Corollary: on large scales, the universe is homogeneous and isotropic- it looks the same in all directions and in all parts – there’s no “center” nor “edge”.

Metric for a homogeneous & isotropic universe:

R(t): scale factor (dimensionless)

))()())((()()( 222222 zyxtRts


The Friedman The Friedman equationequation

- governs the expansion of a uniform gas-filled universe

= Energy density (matter+radiation+vacuum)

- z t (large z small t, “present” R = R0 z=0 ).

- H0 60 km/s/Megaparsec (1 Mpc 3.26 light-year)

3

82

2 NG

R

kH

zR

R

1

1

0

where ,

: Red shift (Doppler effect)

)1( zemitobs N

c G

H

8

3 2

: critical density ( k=0, “flat” universe)


The density The density componentscomponents

c

ii

: density parameter (i=normal matter,

neutrino, dark matter, dark energy, …)

)1(30

)1(3 )1()()( ww zzRR In general,

30 )1()( zzM

40 )1()( zz

0)( z

•Matter: w=0

•Radiation: w=1/3

•Vacuum: w=-1

In a flat universe dominated by:

p

w : equation of state parameter


Geometry of the Geometry of the UniverseUniverse

ii

Current data = 1


Structure Structure formationformation • Jeans instability in self-gravitating systems

cause formation of structures.

• Needs initial seed density fluctuations.

• Density fluctuations grow little in a

radiation- or vacuum-dominated universe.

• Density fluctuations grow linearly in a

matter -dominated universe.

• Baryonic matter alone falls far short of

explaining the level of structure seen today.


Theoretical arguments Theoretical arguments for dark matterfor dark matter

• Spiral galaxies made of bulge+disk: unstable

as a self-gravitating system need a (nearly)

spherical halo.

• With only baryons as matter, structure forma-

tion starts too late for us to exist at this time

– Matter-radiation equality achieved too late,

– Baryon density fluct. can’t grow until decoupling,

– Need larger electrically neutral component.


Size-evolution of the Size-evolution of the universeuniverse


Observational Observational verification verification • A “Standard Model” of cosmology emerges

from extensive surveys of:– Anisotropy in cosmic microwave background

(earliest structures visible, z 3000): CMB

– Large-scale structures (e.g. Galaxies, clusters,

grav. lensing, z 5, dark matter,): LSS– Type 1a supernova brightness & redshift (std.

candles, z 0.5, dark energy): SN1aEach gives a linear equation in M, any two of

these determine M, ; the 3rd serves as a cross-

check.


CMB: CMB: Peeking into the universe’s infancy

with the Wilkinson Microwave Anisotropy Probe


WMAP WMAP talk about thermal resolution!


WMAP WMAP talk about spatial resolution!


LSS: LSS: Surveying galaxies & clusters with normal (HST, SDSS) & x-ray (Chandra, XMM-Newton) vision

The XMM-Newton x-ray observatory


LSS: LSS: Dark matter in galaxy clusters

•Galaxies form clusters bound in a gravitational well.

•Hydrogen gas in the well gets heated, emits x-ray.

•Allows us to determine the baryon fraction of the cluster.


LSS: LSS: Chandra discovers "Rivers Of Gravity" that define the cosmic landscape

Four independent teams of scientists have detected intergalactic gas with temperatures in the range 300,000 to 5 million degrees Celsius by observing quasars with the Chandra X-ray Observatory. An artist's rendering illustrates how X-rays from a distant quasar dim as they pass through a cloud of the intergalactic gas. By measuring the amount of dimming due to oxygen and other elements in the cloud - see the spectrum of the quasar PKS 2155-304 in the inset - astronomers were able to estimate the temperature, density and mass of the absorbing gas cloud.


LSS: LSS: Chandra discovers "Rivers Of Gravity" that define the cosmic landscape


LSS: LSS: Surveying galaxies & clusters with normal (HST, SDSS) & x-ray (Chandra, XMM-Newton) vision

The sky is not so dark in x-ray: HST (L), Chandra (R)


Sloan Digital Sky Survey Sloan Digital Sky Survey (SDSS)(SDSS)


LSSLSSIt is extremely

important to know how the mass and energy, most of it dark, is distributed throughout the universe. A particle theory that contradicts cosmological observations will not be viable.

The M78 nebula, a nursery of stars, as seen by SDSS


LSS & CMB surveys LSS & CMB surveys agreeagree


SN1a: SN1a: measuring the rate of cosmic expansion using high-z supernovae 1a as

standard candles•Nuclear chain reaction in stars with M2Msun (more

complex - binaries etc.)

•As bright as host galaxy

•Brightness not const, but related to fall-off rate.

•Apparent brightness gives distance.

•Red shift (z) gives relative radial velocity.


SN1a: SN1a: Clear evidence of accelerated expansion

•By SCP+HZSNT using HST & ground-based telescopes.

•The cosmological constant fits the bill.

•Can in principle be

something else with –ve p.

•Generally called Dark Energy.


Expansion history of the Expansion history of the universeuniverse


SN1a: SN1a: Next step: the Joint Dark Energy Mission

The proposed Supernova/ Acceleration Probe (SNAP)


The cosmic The cosmic concordanceconcordance•CMB: 1 flat

universe.

•LSS: M 0.3

•SN1a: -2M 0.1• Remarkable agreement

Dark Matter: 23% ± 4%

Dark Energy: 73% ± 4%

(Baryons: 4% ± 0.4%,

Neutrinos: ~0.5%)

• Remarkable precision (~10%)

Remarkable results


Cosmology summary:Cosmology summary:

The current state of knowledge:– The Universe is geometrically flat,

– It is expanding with increasing speed,

– Dark energy dominates matter,

– Dark matter dominates baryonic matter,

– Baryonic matter dominates baryonic antimatter.


Outstanding questions:Outstanding questions:• Dark Matter: What is it? How is it distributed?

• Dark Energy: What is it? Why not ~ 10120? Why not = 0? Does it evolve?

• Baryons: Why not B ≈ 0?

• Ultra-High-Energy Cosmic Rays: What are they? Where do they come from?

…

What tools do we need to address these?


Particle dark matterParticle dark matterSuppose an elementary particle constitutes

DM– WIMP (Weakly Interacting Massive Particle).– Heavy but stable, neutral, produced in early Universe.– Left over from near-complete annihilation.– No such candidate in the SM, must be new physics! – TeV is the right energy scale.– SUSY: the lightest supersymmetric particle (LSP) is a

superpartner of a gauge boson in most models: the “bino” is a perfect candidate for a WIMP.

– There are other possibilities (axino, gravitino, axion, technibaryons, axion, Kaluza-Klein particles, …)

– In any case, we should be able to produce such WIMPs at colliders of the next generation (LHC, ILC).


Neutralino dark matterNeutralino dark matter


The enigma of dark energyThe enigma of dark energy• A naïve estimate of the cosmological

constant in quantum field theory

MPlanck410120 times the onserved value.

• The worst prediction in theoretical physics!

• People had argued that there must be some mechanism to set it to zero.

• But now it seems finite!!!

• Quintessence?– A scalar field slowly rolling down the potential hill.– Will set to 0 when it reaches the minimum?– Must be extremely light: O(10-42 GeV) !!!


Particle physics at the energy Particle physics at the energy

frontierfrontier


The many connectionsThe many connections


ConclusionsConclusions• There’s mounting evidence for non-baryonic dark

matter and dark energy.

• These immediately imply physics beyond the SM.

• Dark matter is likely to be at TeV scale.

• Search for dark matter using

– Collider experiments (LHC, ILC)

– Direct searches (CDMS-II)

– Indirect searches (ICECUBE)

• Dark energy best investigated by JDEM (SNAP?).


The larger US effortsThe larger US effortsFrom the report of the Quantum Universe

subcommittee commissioned by HEPAP (DOE/NSF)


The smaller US effortsThe smaller US effortsFrom the report of the Quantum Universe

subcommittee commissioned by HEPAP (DOE/NSF)


HEPAP recommendation to HEPAP recommendation to DOE/NSFDOE/NSF

(by subpanel on Long Range Planning for U.S. HEP)


OutlookOutlook• A large number of particle physics, astrophysics,

and cosmology projects – both theoretical and experimental – are underway. They complement each other toward a common goal – to solve the most fundamental mysteries of nature.

• It is a truly INTERNATIONAL effort.

• We are living through a revolution in our understanding of the Universe on both the smallest and the largest scales.

• The next decade or two will usher us into a new era of observation and comprehension.


Feel free to contact the speaker

for more information

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THANK THANK YOU!YOU!

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