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Cosmology

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Cosmology Zhaoming Ma July 25, 2007 – PowerPoint PPT presentation

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Title: Cosmology


1
Cosmology
  • Zhaoming Ma
  • July 25, 2007

2
The standard model - not the one youre thinking
  • Smooth, expanding universe (big bang).
  • General relativity controls the dynamics
    (evolution).
  • The universe is homogenous and isotropic, on
    large scales at least (convenience/we know how to
    deal with).

3
Supports to the standard model
velocity
distance
CMB
Hubble diagram
Nucleosynthesis
4
Beyond the standard model - perturbations
Inflation
Baryon and dark matter
5
Put them together
6
Cosmological probes
  • Nucleosynthesis
  • CMB
  • Supernova
  • Weak gravitational lensing
  • Galaxy cluster
  • Baryon acoustic oscillation

7
Precision cosmology - where we stand
8
Precision cosmology - the future
  • What is dark energy? Or do we need to modify
    gravity theory instead?
  • More and more supernova is and will be collected.
  • Deeper, wider and higher precision weak lensng
    surveys are planed.
  • Dedicated BAO surveys are in consideration.

9
Weak gravitational lensing
  • Ellipticity describe the shape of a galaxy.
  • Shear if the unlensed galaxies
    are circular.
  • Shear power spectrum constrains cosmology

10
Weak lensing as cosmological probe
Shear power spectrum
Matter power spectrum
Source galaxy distribution
Weighting function

To constrain cosmology, we have to know this!
Kaiser 1998
11
Photo-z parametrization
zs2.6,2.7
zs0.5,0.6
12
Photo-z calibration
13
Linear v.s. Nonlinear P(k)
Data nonlinear
Theory linear
Simulation
OR
Higher order pert. theory?
Tegmark et al 2003
14
Fitting formulas
  • Simulation is expensive, so fitting formulas are
    developed.
  • HKLM relation
  • Hamilton et al 1991
  • Peacock Dodds 1996
  • Halo model
  • Smith et al 2003 (10)
  • i) translinear regime HKLM
  • ii) deep nonlinear regime
  • halo model fit

15
Foundations of fitting formulas
  • HKLM relation or Halo model.
  • Nonlinear power is determined by linear power at
    the same epoch history of linear power spectrum
    doesnt matter.

Q are these physically sound assumptions?
16
Tools to test these assumptions
  • Use the public PM code developed by Anatoly
    Klypin Jon Holtzman
  • Modified to take arbitrary initial input power
    spectrum
  • Modified to handle dark energy models with
    arbitrary equation of state w(z)

17
The difference a spike makes
  • Compare P(k) from simulations w/ and w/o a spike
    in the initial power
  • Peak is smeared by nonlinear evolution
  • More nonlinear power at all kNL with no k
    dependency
  • HKLM scaling would predict the peak being mapped
    to a particular kNL

18
Halo model prediction
  • The peak is not smeared
  • The peak boosts power at all nonlinear scales
  • Slight scale dependency

19
Does P(k) depend on growth history?
20
History does matter
  • Linear part of the power
  • spectra are consistent (by
  • construction)
  • Nonlinear power spectra
  • differ by about 2 simply
  • due to the differences in the
  • linear growth histories
  • This is not the maximum
  • effect, but already at the
  • level that future surveys care
  • (1 Huterer et al 2005)

21
Matching growth histories
22
Same growth histories ltgt same P(k)
  • Linear part of the power
  • spectra are consistent with the
  • differences in the linear growth
  • Nonlinear part of the power
  • spectra are also consistent given
  • the differences in the linear part
  • Result validates the conventional
  • wisdom that the same linear
  • growth histories produce the
  • same nonlinear power spectra
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