Eric Linder

1
Seeing Darkness The New Cosmology
Eric Linder University of California,
Berkeley Lawrence Berkeley National Lab
2
New Frontiers
Beyond Einstein What happens when gravity is no
longer an attractive force?
Scientific American
Discovery (SCP,HiZ 1998) 70 of the universe
acts this way! Fundamentally new physics.
Cosmology is the key.
3
Cosmic Coincidence
Is this mysterious dark energy the original
cosmological constant ?, a quantum zeropoint sea?
Think of the energy in ? as the level of the
quantum sea. At most times in history, matter
is either drowned or dry.
Dark energy
Matter
Today
4
On Beyond ?!
We need to explore further frontiers in high
energy physics, gravitation, and cosmology. New
quantum physics? Does nothing weigh something?
Einsteins cosmological constant, Quintessence,
M/String theory New gravitational physics? Is
nowhere somewhere? Quantum gravity, supergravity,
extra dimensions? We need new, highly precise
data
5
Cosmic Archaeology
CMB direct probe of quantum fluctuations Time
0.003 of the present age of the universe. (When
you were 0.003 of your present age, you were 2
cells big!)
6
Standard Candles
Brightness tells us distance away (lookback
time) Redshift measured tells us expansion
factor (average distance between galaxies)
7
What makes SN measurement special? Control of
systematic uncertainties
Each supernova is sending us a rich stream of
information about itself.
Images
Nature of Dark Energy
Redshift SN Properties
Spectra
data
analysis
physics
8
Astrophysical Uncertainties
For accurate and precision cosmology, need to
identify and control systematic uncertainties.
9
Beyond Gaussian
Gravitational lensing Few hi z SN ? poor PDF
sampling Flux vs. magnitude bias
Holz Linder 2004
Extinction bias One sided prior biases
results Dust correction crucial need NIR
10
Gravitational Lensing
Gravity bends light - we can
detect dark matter through its gravity, -
objects are magnified and distorted, -
we can view CAT scans of growth of structure
11
Gravitational Lensing
Lensing measures the mass of clusters of
galaxies. By looking at lensing of sources at
different distances (times), we measure the
growth of mass. Clusters grow by swallowing more
and more galaxies, more mass.
Acceleration - stretching space - shuts off
growth, by keeping galaxies apart. So by
measuring the growth history, lensing can detect
the level of acceleration, the amount of dark
energy.
12
Dark Energy The Next Generation
wide
9000? the Hubble Deep Field plus 1/2 Million ? HDF
Redshifts z0-1.7 Exploring the last 10
billion years 70 of the age of the universe
deep
colorful
Both optical and infrared wavelengths to see thru
dust.
SNAP Supernova/Acceleration Probe
13
Exploring Dark Energy
14
Quintessence
Scalar field ? with Lagrangian L? (1/2)(???)2
- V(?)
.
Energy density ?? (1/2) ? 2 V(?) Pressure
p? (1/2) ? 2 - V(?)
.
Einstein gravity says gravitating mass ?3p, so
acceleration if equation of state ratio w p/?
lt -1/3 w (K-V) / (KV) Potential energy
dominates (slow roll) V gtgt K ? w -1 Kinetic
energy dominates (fast roll) K gtgt V ? w
1 ?(a) e3?dln a 1w(a) a-3(1w) Dynamics
important! Value and running w, w?wa /2
Equation of state model w(a) w0wa(1-a)
15
Equation of State
Reconstruction from EOS ?(a) ?? ?c exp 3
?dln a 1w(z) ?(a) ?dln a H-1 sqrt ?(a)
1w(z) V(a) (1/2) ?(a) 1-w(z) K(a)
(1/2) 2 (1/2) ?(a) 1w(z)
But, ?(1w)? ?(1w) HMp So if 1w ltlt 1,
then ?? /H ltlt Mp. It is very hard to
directly reconstruct the potential.
16
Dynamics of Quintessence

• Equation of motion of scalar field
• driven by steepness of potential
• slowed by Hubble friction
• Broad categorization -- which term dominates
• field rolls but decelerates as dominates energy
• field starts frozen by Hubble drag and then
  rolls
• Freezers vs. Thawers

17
Limits of Quintessence
Distinct, narrow regions of w-w? Works for
linear, quadratic, quartic, PNGB, ?-n, SUGRA,
exponential
Caldwell Linder 2005 PRL astro-ph/0505494
Entire thawing region looks like wconstant
-10.05. Need w? experiments with ? (w?)
2(1w).
18
Phantoms without Ghosts
5 Ways to have w lt -1 without bad physics
What do you mean bad? Imagine all life as
you know it stopping instantaneously and every
molecule in your body exploding at the speed of
light. -- Ghostbusters

• Vacuum metamorphosis Parker Raval 1999 PRD
  60, 063512
• Coupling weffw-?/(3H) Turner 1985, Linder
  1988, Linder 2005
• Curvature ?totalgt1 (kgt0) ? ? weff lt -1 Linder
  0508333
• Climbing field (or k-essence) Csaki, Kaloper,
  Terning 0507148
• Two components, e.g. brane? Lue Starkman
  2004, CKT 2005

19
Expansion History
Observations that map out expansion history a(t),
or w(a), tell us about the fundamental physics of
dark energy. Alterations to Friedmann framework
? w(a)
Suppose we admit our ignorance H2 (8?/3) ?m
?H2(a) Effective equation of state w(a) -1 -
(1/3) dln (?H2) / dln a Modifications of the
expansion history are equivalent to time
variation w(a). Period.
gravitational extensions or high energy physics
20
Expansion History
For modifications ?H2, define an effective scalar
field with V (3MP2/8?) ?H2 (MP2H02/16?) d
?H2/d ln a K - (MP2H02/16?) d ?H2/d ln a
Example ?H2 A(?m)n w -1n Example ?H2
(8?/3) f(?m) - ?m w -1 (f?-1)/ f/?m - 1
21
Revealing Physics

• Time variation w(z) is a critical clue to
  fundamental physics.
• Modifications of the expansion history w(z).
• But need an underlying theory - ??? beyond
  Einstein gravity?
• Growth history and expansion history work
  together.

Linder 2004, Phys. Rev. D 70, 023511 cf. Lue,
Scoccimarro, Starkman Phys. Rev. D 69 (2004)
124015 for braneworld perturbations
22
Physics of Growth
Growth g(a)(??/?)/a depends purely on the
expansion history H(z) -- and gravity theory.
Expansion effects via w(z), but separate effects
of gravity on growth.
g(a) exp ?0ad ln a ?m(a)? -1
Linder 2005 PRD astro-ph/0507263
Growth index ? 0.550.051w(z1) Works to
0.05 0.2!
23
Growth and Expansion
With ? as free fit parameter, we can test
framework, and the origin of dark energy.
Keep expansion history as w(z), growth deviation
from expansion by ?.
New paradigm To reveal the origin of dark
energy, measure w, w?, and ?. e.g. use SNWL.
24
Going Nonlinear
This gives a high accuracy approach to growth
factor, i.e. linear mass power spectrum. Can we
get high accuracy for the nonlinear power
spectrum?
Linder White, Phys. Rev. D Rapid
astro-ph/0508401

• New prescription
• Normalize gtoday, i.e. scale by ?8.
• Match different cosmologies (i.e. ws) growth
  at z1.8 this determines ?M.
• Fix h by using invariant ?Mh2.

It works! Relative precision on Pkfull to lt1.5
over z0-3. NB fit functions were only good to
10 -- for ?.
25
Going Nonlinear
Efficient generation of grid of dark energy
cosmologies w(z)
New discovery growth ? dlss So our
prescription automatically includes CMB priors!
26
Todays Inflation
Map the expansion history precisely and see the
transition from acceleration to deceleration.
Test the cosmology framework alternative
gravitation, higher dimensions, etc.
27
The Next Physics
The Standard Model gives us commanding knowledge
about physics -- 5 of the universe (or 50
of its age). What is dark energy? Will the
universe expansion accelerate forever? Does the
vacuum decay? Phase transitions? How many
dimensions are there? How are quantum physics
and gravity unified? What is the fate of the
universe? That 5 contains two fundamental
forces and a zoo of elementary particles. What
will we learn from the dark sector?!
How can we not seek to find out?