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MAY 8, 2007 CCAPP, OSU. Voids of dark energy. Irit Maor Case Western Reserve University With Sourish Dutta PRD 75, gr-qc/0612027. A very quick summary:. The universe is accelerating. [kinematics] We do not know why. [dynamics] Cosmological constant? 120 orders of magnitude!. 0. 1.

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voids of dark energy

MAY 8, 2007

CCAPP, OSU

Voids of dark energy

Irit Maor

Case Western Reserve University

With Sourish Dutta

PRD 75, gr-qc/0612027

a very quick summary
A very quick summary:

The universe is accelerating. [kinematics]

We do not know why. [dynamics]

Cosmological constant?

120 orders of magnitude!

slide3

0

1

2

8

+

1

0

6

2

¡

:

w

=

0

0

7

9

¡

:

:

wmap3:

“wmap does not need quintessence ” (Page)

but cmb needs something else
But: “CMB needs something else”

Many degeneracies for w(z). Maor et al, 0007297Upadhye et al, 0411803

Which parameters? Liddle, 0401198

Which priors? Maor et al, 0112526

Which data sets? Bridle et al, 0303180

motivation for dynamical dark energy

(

)

6

1

¡

w

w

z

=

=

Motivation for dynamical dark energy
  • A mild generalization of the old standard cosmological model.
  • Scalar fields are not a new concept, “inspired” by fundamental theories.
  • Hopes for dynamical fine tuning.
  • Probably an ok description of more complicated scenarios.
slide7
..but:

tracker, k-essence, phantom, coupled, …your favourite DDE model

fine tuning not solved!

other alternatives
Other alternatives

SN are wrong

Xtra dimensions ( effective w(z) or coupled DDE)

your favourite theory of gravity ( same as above)

super horizon modes

the background

d

w

d

w

0

z

The background:

  • #% for

maybe #% for

BAO

Clusters

CMB

ISW

SN

SZ

WL

Background measurements will have a very hard time differentiating between CC and DDE.

All focus on w(z).

Null experiments, how far?

looking for the dark stuff
Looking for the dark stuff

Solar system

Extrapolation from the cosmic to the solar scale.

Clear signature of dark gravity!

looking for the dark stuff1
Looking for the dark stuff

Perturbations

Does DDE cluster on scales less than ~100 Mpc?

(yes)

A thorough understanding of the behaviour of perturbations is needed.

If it clusters, it is not the cosmological constant!!

looking for the dark stuff2
Looking for the dark stuff

Non linear regime

how does the DDE behave?

model sensitivity vs generality?

In progress, with Dutta

large scale cmb
Large Scale, CMB

Weller and Lewis, 0307104

slide19

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1

¼

1

2

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H

2

m

0

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V

L

¡

2

=

Á

¹

m

2

L

L

L

L

L

G

+

+

=

Á

G

m

Standard gravitational action

Standard pressureless fluid

linear perturbation

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t

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t

+

+

¡

+

+

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½

s

r

r

½

a

½

r

r

r

r

r

r

=

!

!

=

m

m

;

;

;

;

;

;

;

Linear perturbation

(Synchronous gauge)

the equations
The equations
  • Zeroth order: standard FRW evolution of the background.
  • First order: equations for the perturbation variables, which after a Fourier transformation are ODE’s.
initial conditions
Initial conditions
  • Matter: gaussian, with width well within the horizon.
  • Scalar field: homogeneous IC, with no kinetic energy (w=-1).
  • Metric: by the constraints equations.

Results are insensitive to IC

results
Results

Anti-correlation between matter and DE perturbations

results1
Results

Amplitude grows fast!

results2
Results

“cross-over”

equation of state

¡

¢

1

±

±

±

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w

p

w

½

=

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2

0

1

Á

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0

p

0

2

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=

=

0

±

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1

+

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w

w

0

=

1

0

2

Equation of State

Background EOS

Linear correction to EOS

First order corrected EOS

equation of state1
Equation of state

Spatial profile of the equation of state

void formation

_

_

2

±

Á

±

Á

Á

±

Á

+

½

m

=

Á

Void formation

Energy density correction:

PE correction < 0

KE correction > 0

KE correction quickly dominates void

slide30

_

_

±

K

E

0

±

Á

>

0

±

Á

P

E

0

0

<

<

<

±

Á

0

<

Á

0

>

Acceleration slows, but doesn’t change sign.

conclusions
Conclusions

DDE develops voids [ripples].

Our results are generic for slow-roll DDE.

Possible interesting dynamics in the non-linear regime.

Observables?