cosmology - ubc physics & astronomy | ubc physics &...

Cosmology

Scott Dodelson Penticton Workshop

Two Success Stories: Cosmology & Particle Physics

We know much

We understand little

How you can help

1June 13, 2011


Consider the United States in 1790

Over-densities of order 50

Concentrated in East

Vast Voids with low density

2June 13, 2011

June 13, 2011 Scott Dodelson Penticton Workshop

Consider the United States Today

Over-densities of order 10,000

Concentration in coasts

Traces of primordial density (Boston-Washington; East > West)

Vast Voids

3


The story of this evolution is the story of the United States

When we understand the evolution from one map to another, we can understand the sociological, economic, and political forces acting on the US the people, or the constituents, of the US

4June 13, 2011

Less provincially, we have detailed maps of the Universe at two epochs


5

COBE

Sloan Digital Sky Survey

(SDSS)

Map of the photons, electrons, & protons when the Universe was 400,000 years old

Map of the galaxy distribution in the Universe today

Standard Model of Particle Physics

4 particles which mediate the fundamental forces (photon, 2 W’s, Z)

Two Fermions (Electron and Neutrino) Higgs particle: Responsible for Mass

6Scott Dodelson Penticton Workshop

June 13, 2011

Three minor extensions (all of which won Nobel Prizes)

Quarks as well as leptons

Quantum Chromodynamics: gluons and their interactions

Three generations: electron, muon, tau (and similarly for quarks)


June 13, 2011

The Standard Model explains everything ever produced in an accelerator

One page (out of 298) from the Particle Data Group Booklet

June 13, 2011 8Scott Dodelson Penticton Workshop

and is consistent with all observed phenomena (not necessarily a good thing)

The Cosmic Story requires new physics


9

COBE

Sloan Digital Sky Survey

(SDSS)

At t=400,000 years (z=1000), the photon/baryon distribution was smooth to one part in 10,000.

General Relativity predicts that perturbations have grown since then by a factor of 1000

Dark Matter Solves Cosmic Structure Problem

ClumpinessDark matter was much clumpier than baryons were at the time of the picture of cosmic microwave background (CMB). Enough time for structure to grow!

Large Scales


10June 13, 2011

Two Stories Complement One Another

Cosmic Story requires Dark Matter, which cannot be explained by Standard Model of Particle Physics

This is the simplest example of how detailed study of cosmological maps leads to (i) a coherent story for cosmic evolution and (ii) understanding of new physicsJune 13, 2011 Scott Dodelson

Penticton Workshop11

Inflation

Dark Matter

Neutrino Mass

Dark Energy

Dark Energy

LHC

Previous Accelerators

Detailed Analysis of Maps


12

Neutrinos

Massive neutrinos contribute to the energy density

This fraction of the matter does not clump on small scales

Produces relatively large changes in the power spectrum of matter

June 13, 2011 Scott DodelsonPenticton Workshop

13

eV

mf

matter 108.0


Even for a small neutrino mass, get large impact on structure: power spectrum is excellent probe of neutrino mass

14

Neutrinos

Current Constraints

Strongest constraint on sum of neutrino masses

Oscillation experiments measure difference of squared masses

Sum of the neutrino masses must be greater than 0.05 eV

Ichiki, Takada, & Takahashi 2009

June 13, 2011 15Scott DodelsonPenticton Workshop

Dark Matter

Physics of the CMB

Pressure of radiation acts against clumping

If a region gets overdense, pressure acts to reduce the density: restoring force

June 13, 2011 16Scott Dodelson Penticton Workshop

Dark Matter

C note on a guitar


June 13, 2011

Dark Matter

CMB is different because …

Fourier Transform of spatial, not temporal, signal

Time scale much longer (400,000 yrs vs. 1/260 sec)

No finite length: all k allowed!


June 13, 2011

Dark Matter

Why are there peaks & troughs in CMB Spectrum?

Vibrating String: Characteristic frequencies because ends are tied down

Temperature in the Universe: Small scale modes begin oscillating earlier than large scale modes

Fou

rier

Am

plit

ud

e


June 13, 2011

Dark Matter


20

)()4/31(3

2

FTk

Tb

Detailed shape depend on matter & baryon densities

Forced Harmonic Oscillator

Dark Matter


21

Dark Matter

CMB and Matter power spectra give consistent results

Require dark matter even for the shape

Total matter density well-constrained


22

Dark Energy

Einstein’s Equations applied to the Universe yield the Friedmann Equation


23

2

2

0

2

)1())(1(1

3exp zzwz

dz

H

Hk

i

ii

Curvature density (=0 from position of CMB

peaks)

Eqn of state (pressure/energy density)

of species iw=0 for matter

1/3 for radiation

Energy density of species i in units of the

critical density

Dark Energy

This equation does not hold today!


24

i

iik zwz

dzz

H

H))(1(

13exp)1( 2

2

0

2

01 m

Einstein’s Equations applied to the Universe yield

2

2

0

2

)1())(1(1

3exp zzwz

dz

H

Hk

i

ii

Scott DodelsonPenticton Workshop

Introduce New Substance Dark Energy

Dar

k En

ergy

Den

sity

Matter Density

Dark Energy density remains roughly constant as universe expands Nothing like this in Standard Model It’s not just CMB + Galaxy Map: Supernovae also require dark energy

25June 13, 2011

Galaxy Map


The Horizon Problem

Hubble Radius (Distance light travels as the Universe doubles in size) at t=400,000 years

How are these two spots correlated with one another?

26June 13, 2011


The Horizon ProblemD

ista

nce

Time

t = 400,000 yrs

Hubble Radius

Distance between 2 spots in CMB

27June 13, 2011



ista

nce

Time

t = 400,000 yrs


Hubble Radius

28June 13, 2011



ista

nce

Time

t = 400,000 yrs


Hubble Radius

29June 13, 2011


Dis

tan

ce

Time

t = 400,000 yrs

Inflation Solves the Horizon Problem

Inflation


Hubble Radius

30June 13, 2011


Quantum Mechanical Fluctuations

Ubiquitous on the sub-atomic level …

Inflation stretches them to astronomical sizes

31June 13, 2011


Seeds of Structure

Quantum mechanicalfluctuations generated during inflation Perturbations freeze outwhen distances get larger than horizon Evolution when perturbations re-enter horizon

Dis

tort

ion

s in

Sp

ace-

Tim

e

32June 13, 2011

Evidence for Inflation

The perturbation corresponding to each mode need not have zero initial velocity.

We implicitly assumed that every mode started with zero velocity.


June 13, 2011

At every wavelength (or angular scale), we are averaging over many modes with different directions.

34Scott DodelsonPenticton Workshop

June 13, 2011

Interference would destroy peak structure

There are many, many modes with

similar values of k. All have different initial amplitude. Why all they are in phase?

First Peak Modes

t/400,000 yrs

Fou

rier

Am

plit

ud

e


June 13, 2011

Infinite number of guitars are synchronized

Similarly, all modes corresponding to first trough are in

phase: they all have zero amplitude at

recombination. Why?

t/400,000 yrs

Fou

rier

Am

plit

ud

e


June 13, 2011

First Trough Modes

Without synchronization:

First “Peak” First “Trough”

We will NOT get series of peaks and troughs!

t/400,000 yrs t/400,000 yrs

Fou

rier

Am

plit

ud

e

Fou

rier

Am

plit

ud

e


June 13, 2011

Spectrum of Anisotropies Evidence for Synchronization


DASI, Boomerang, Maxima (2001)

WM

AP

(2009)

Coherent series of Peaks and Troughs emerges because all Fourier modes shared the same temporal phase

38June 13, 2011

We know much

Neutrino masses are light and they affect structure formation at a potentially detectable level

85% of all matter is something new, dark matter, not found in the Standard Model

The Universe is accelerating today presumably because 71% of the energy is a new substance, dark energy

The seeds of structure were planted during inflation, an early epoch of acceleration


39

We understand little

Why are neutrino masses so small? What is the sum of neutrino masses (must be >0.05 eV)? Normal or inverted hierarchy?

What is the dark matter? It is not part of the Standard Model. Supersymmetry?

Why and when does the Friedmann equation break down? Dark Energy? Modified Gravity? Something else?

Did inflation happen? What is the physics behind inflation? Grand Unified Theory? Something more exotic?


40

Neutrino Mass

Optimistic projections suggest that future 21 cm experiments will detect neutrino mass to 10-sigma

Can distinguish normal from inverted hierarchy (see right)


41

Pritchard & Pierpaoli 2008

z=0

z=8

eVm 12.0

Dark Energy

Squares for Cylindrical Radio Telescope+Planck; Crosses add previous experiments

Fiducial: L=100m; Width=14m; Duty Factor=0.5

For comparison, Dark Energy Survey proposal lists FoM=264June 13, 2011 Scott Dodelson

Penticton Workshop42

Seo et al., 2010

Dark Energy vs. Modified Gravity


43

Masui, Schmidt, Pen, & McDonald 2010

Models have identical expansion histories. Error bars assume a 200mx200m cylindrical telescope

Non-Gaussianity in Inflation


44

Joudaki et al. 2011

Importance of Foreground Removal: x-axis sets largest scale above which foregrounds can be removed

Comparable to Planck

There is a lot left to explore

Modern cosmology depends on maps. We have explored roughly the same fraction of the universe as Penticton covers of Canada. Surprises are on the horizon!


45

cosmology - ubc physics & astronomy | ubc physics &...

Documents