Simulation of Gravity-Driven Flow Through a Microfluidic ...
Testing modified gravity beyond cosmic...
Transcript of Testing modified gravity beyond cosmic...
Testing modified gravity beyond cosmic variance
Caitlin Adams Supervised by Professor Chris Blake
Large Scale Structure and Galaxy Flows, Quy Nhon — 08/07/16
Aims
Caitlin Adams — Large Scale Structure and Galaxy Flows
How can we distinguish between ΛCDM and alternatives?
How can we best utilise low-redshift surveys?
Can we overcome cosmic variance in a self-consistent way?
The standard model
Image from NASA/WMAP
ΛCDM attributes accelerated expansion to dark energy
but could there be an alternative explanation?
Caitlin Adams — Large Scale Structure and Galaxy Flows
Modified gravity
Many physicists are exploring extensions to GR
There are some well established models: f(R) models - extending functional form of GR Galileon models - addition of a scalar field Massive gravity models - graviton has mass
There’s also work on observational predictions from generalised forms of modified gravity (Baker et al. 2014)
Caitlin Adams — Large Scale Structure and Galaxy Flows
Scale-dependence
Caitlin Adams — Large Scale Structure and Galaxy Flows
Scale-dependence: 6dFGS
Data from Johnson et al. 2014
Caitlin Adams — Large Scale Structure and Galaxy Flows
Cosmic variance
Measurements on large scales at low redshift are limited by sample variance from the overdensity field
A single tracer is limited by this variance
But the ratio of tracers is not!
Caitlin Adams — Large Scale Structure and Galaxy Flows
Covariance model
we can construct
where
For data vector
Caitlin Adams — Large Scale Structure and Galaxy Flows
Covariance model
free parameters:
Caitlin Adams — Large Scale Structure and Galaxy Flows
0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46f�8
0.8
1.0
1.2
1.4
1.6
1.8
b�8
0.8 1.0 1.2 1.4 1.6 1.8b�8
GiggleZ �g-vp Correlated
0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46f�8
0.8
1.0
1.2
1.4
1.6
1.8
b�8
0.8 1.0 1.2 1.4 1.6 1.8b�8
GiggleZ �g-vp Independent
Results: GiggleZ simulation
Caitlin Adams — Large Scale Structure and Galaxy Flows
0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46f�8
0.8
1.0
1.2
1.4
1.6
1.8
b�8
0.8 1.0 1.2 1.4 1.6 1.8b�8
GiggleZ �g-vp Independent
0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46f�8
0.8
1.0
1.2
1.4
1.6
1.8
b�8
0.8 1.0 1.2 1.4 1.6 1.8b�8
GiggleZ �g-vp Correlated
Results: GiggleZ simulation
Caitlin Adams — Large Scale Structure and Galaxy Flows
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9f�8
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
�
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
�
6dF �g-vp Independent
Results: 6dFGS
Preliminary
Caitlin Adams — Large Scale Structure and Galaxy Flows
Upcoming: Taipan
Koda et al. 2014
Constraint (β)
6dFGS 16%
Taipan 7.4%
WALLABY 3.8%
Caitlin Adams — Large Scale Structure and Galaxy Flows
Take home points
Scale-dependent measurements can distinguish between the standard model and modified gravity models
Modelling the covariance of velocities and overdensities will provide a measure of β(k)
Beating down cosmic variance through multiple probes will provide tighter constraints on f(k)
Caitlin Adams — Large Scale Structure and Galaxy Flows
Bonus Slide: Peculiar velocities
In Fourier Space:
1/k dependence means velocities are sensitive to large modes (small k)
Koda et al. 2014
Caitlin Adams — Large Scale Structure and Galaxy Flows
Bonus Slide: Peculiar velocities
Johnson et al. 2014
Peculiar velocities are non-Gaussian, so apply a transform:
For:
measured from Fundamental Plane
Hui & Greene 2006
Caitlin Adams — Large Scale Structure and Galaxy Flows
Bonus Slide: Exact equations
n
0
W (k)
j0(kr)
aH(r̂ · x̂v)
(aH)
2
1
3
cos↵ (j0(kr)� 2j2(kr)) +x�xv
r2j2(kr) sin
2 ↵
�
1
Nexpi
0
Caitlin Adams — Large Scale Structure and Galaxy Flows