BAOs (Baryon Acoustic Oscillations)

1
Accuracy of Cosmological N-body Simulations
DARK ENERGY
Ludwig-Maximilians-University, Munich
Takahiro Nishimichi (the Univ. of Tokyo)
Introduction

• BAOs (Baryon Acoustic Oscillations)
• A promising tool to access dark energy.
• Demand for more accurate theoretical modeling
• Nonlinearity of gravitational structure formation
• Redshift-space distortion
• Galaxy biasing
• Methods
• Perturbation theory
• Newly developed renormalized perturbation theory
• N-body simulations
• 1 error on BAO scale -gt 35 Error on DE e.o.s.
• Is the currently achieved accuracy enough?

Our simulations
After correction
2LPT
Gadget2

• SPT standard perturbation theory
• RPT renormalized perturbation theory
  (CrocceScoccimarro06a,b,08)
• CLA closure approximation (TaruyaHiramatsu08)
• LIN linear theory
• Convergence test is difficult from this figure
  because of large errorbars due to small total
  volume of N-body simulations (4h-3Gpc3).

• Errorbars largely reduced to sub-percent level!
• The three nonlinear models and N-body simulations
  agree at largest scales (klt0.05hMpc-1).
• RPT, CLA and N-body simulations agree within
  errorbars in almost the same range for a given
  redshift.
• RPT and CLA have better convergence properties
  than SPT in the plotted ranges.

Correction for finiteness of volume
Errorbars
2pt correlation (preliminary)
Recovery of BAOs
Convergence regime
C is a constant to be determined.
Preliminary

• M08 Matsubara08
• SK07 SefusattiKomatsu07
• JK06 JeongKomatsu06

• We construct smooth reference spectra using
  B-spline fit. (e.g., Percival07, Nishimichi07)
• The convergence regimes for the extracted BAO
  phases are wider than those for the amplitudes of
  P(k) (vertical arrows).
• The scale shift parameter a can be constrained
  tightly using the modes within our convergence
  regimes alone.

• The number of N-body realizations increased to
  30.
• A good convergence in real space?
• Monopole and quadrupole moments are reasonably
  converged in redshift space?

• We determined the 1 and 3 convergence regimes
  where theoretical predictions and N-body
  simulations agree within 1 and 3.
• Our formula explains the results (symbols) very
  well.

Apendix convergence test of our simulations
Initial condition
SPT w/o cutoff scale
N-body code
Fake agreement of SPT for small boxsize
boxsize
2LPT vs. ZA
RPT w/ cutoff scale