Self-similar Bumps and Wiggles: Isolating the Evolution of the BAO Peak with

Power-law Initial Conditions

Chris Orban (OSU Physics) with

David Weinberg (OSU Astronomy)

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BackgroundEarly Universe Late Universe

credit: SDSScredit: WMAP

Eisenstein et al. 2005

Problem:

How does the BAO signature change over cosmic time?

How “standard” is this standard ruler?Opportunity:

Largest “ruler” ever discovered – very useful for distance scale, dark energy

Anchored to CMB (not LMC!)Challenge:

Need to observe large cosmological volumes!

Need sub-percent accurate theory for any w(z)!

Initial Conditions

FourierTransform

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Linear regime

Strongly non-linear regime

Chris Orban – Self-similar Bumps and Wiggles

Non-linear structure formation

Chris Orban – Self-similar Bumps and Wiggles

Simplifying the Problem

Chris Orban – Self-similar Bumps and Wiggles

Self-similar Bumps!

rbao / Lbox = 1 / 10

rbao / np1/3 = 100/8

rbao / Lbox = 1 / 20

!!!

!!!

• Because of self-similarity the bump evolution should be exactly the same as a scaling of the previous results

• Comparing results from rbao x2 simulations (e.g. rbao = 200 h-1Mpc) to previous results

• Numerical effects may break self-similarity – a test more powerful and more general than convergence testing

• Can’t do this with CDM initial conditions!

Fourier-space phenomenology

PNL(k) = exp(-2k2/2) PL(k/) + A(k)

DampingNon-linear spectrum

Small-scale model

Initial spectrum shift!

Beyond linear-order

1-loop SPT predictions!

PT valid

PT breaks down•Many groups developing beyond-linear-order perturbation theory methods to describe BAO evolution

•If successful BAO evolution for arbitrary w(z) can be computed without N-body simulations

•Powerlaw setup is problematic for many of these methods – may point to better schemes

Chris Orban – Self-similar Bumps and Wiggles

1-loop SPT predictions from publically-available code:http://mwhite.berkeley.edu/Copter/

(Carlson, White, & Padmanabhan 2009)

Future Plans

• Run “powerlaw” setup with 0• Explore the broadening of the BAO feature in

the halo clustering• Run simulations with a different N-body code

(PKDGRAV instead of Gadget2)• Compare and develop phenomenological

models to describe non-linear evolution

Chris Orban – Self-similar Bumps and Wiggles