Constraining Cosmology in the Planck Era

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Constraining Cosmologyin the Planck Era

• Martin White
• University of California, Berkeley

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Outline

• A decade of discovery 1992-2002
• How far weve come
• The near future
• The Planck Epoch
• Primary CMB anisotropies
• Testing inflation within the decade
• The universe at z1000
• Dark energy
• Secondary CMB anisotropies
• A CMB centric view of structure formation

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1992(2)-2002(1)
White, Scott Silk (1994)
WMAP 1st year data ext
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The Planck Epoch
Planck has the resolution, sensitivity and
frequency coverage to provide precise
measurements of the CMB power spectra.
(1yr)
Temperature
Polarization
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Precise measurements precise theory science

• What kinds of science questions are enabled by
  such precise measurements?
• Primary CMB anisotropies
• Testing inflation within the decade
• The universe at z1000
• Dark energy
• Secondary CMB anisotropies
• A CMB centric view of structure formation

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A prediction of inflation?

• Inflation predicts an almost scale-invariant
  spectrum of (adiabatic) density perturbations
  were produced in the early universe.
• Deviations from scale-invariance tell us about
  the inflaton potential.
• Deviations from a power-law spectrum tell us we
  dont understand inflation as well as we thought!
• The what else could it be theory also predicts
  a scale-invariant spectrum of perturbations.
• Observationally detecting a deviation from
  scale-invariance would be (yet another?) triumph
  for inflation theory.
• A long lever arm and both temperature and
  polarization power spectrum make Planck a
  wonderful experiment for testing inflation!

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Testing inflation with the CMB

• Measure ns and running
• Expect dns0.04(0.02) 0.007 and da0.02
  0.003
• c.f. WMAP longer level arm, more spectra
• Also break (accidental n-t) degeneracy with EE

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Testing inflation with the CMB

• Rule out ? isocurvature contribution
• Constrain features in the primordial P(k)
• Trans-Planckian effects,
• Find large-angle GW signal ?
• Would measure the expansion rate during
  inflation.
• Constrain tensors down to a few percent of the
  scalar contribution.
• Testing Gaussianity
• Increased S/N dramatically tightens constraints
  on non-Gaussianity in the CMB (-58 lt fNLlt134 at
  95CL) to fNL1.

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The universe at z1000 cosmological parameters

• Detailed observations of the CMB anisotropy
  constrain the high redshift universe.
• Most strongly constrained is the physics which
  gives rise to the acoustic peaks in the CMB power
  spectrum.
• CMB gives wm, wb, qA or lA.
• From this can derive other constraints, e.g.
  D(z1100)
• Currently dD(z1100) 3
• Limited by uncertainty in wm (dwm 8)
• Key is higher peaks.
• Planck should get dwm0.9.
• An important constraint for dark energy and to
  calibrate the baryon oscillation method for
  measuring DA(z) H(z)
• In principle dD(z1100) 0.2!

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The cartoon

• At early times the universe was hot, dense and
  ionized. Photons and matter were tightly coupled
  by Thomson scattering.
• Short m.f.p. allows fluid approximation
  baryon-photon fluid
• Initial fluctuations in density and gravitational
  potential drive acoustic waves in the fluid
  compressions and rarefactions.
• A sudden recombination decouples the radiation
  and matter, giving us a snapshot of the fluid at
  last scattering.

harmonic wave
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Acoustic oscillations seen!
First compression, at kcstlsp. Density maxm,
velocity null.
Velocity maximum
First rarefaction peak at kcstls2p
Acoustic scale is set by the sound horizon at
last scattering s cstls
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Sound horizon more carefully

• In an expanding universe, and with the relative
  densities of photons and baryons evolving, the
  expression for the sound horizon is not longer
  simply scstls
• Depends on expansion of universe
• Matter and radiation density H2 8pG (rm rr
  )
• and the baryon-to-photon ratio (through cs)

Photon density is known exquisitely well from CMB
spectrum.
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CMB calibration

• Not coincidentally the sound horizon is extremely
  well determined by the structure of the acoustic
  peaks in the CMB.
• Knowledge of the physical scale, s, and the
  angular scale of the peaks, qA, gives the
  distance to last scattering D through sD qA.
• The same physical scale is imprinted upon the
  matter power spectrum, and can serve as a
  calibrated standard ruler at low-z. (D.
  Eisenstein)

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Matter power spectrum P(k)
Wb wm
wm
Total matter power spectrum
Eisenstein (2002)
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A calibrated standard ruler
Both the large-scale peak in the matter power
spectrum and the fine-scale wiggles are well
calibrated by the CMB.
Meiksin, White Peacock
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The missing piece is the matter density
The key is the higher peaks

• The CMB anisotropies are damped at small angular
  scales by photon diffusion. Well understood!
• Removing this shows the effects of baryons and
  the epoch of equality.

Hu White (1997)
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Baryon loading and the potential envelope

• Baryons give weight to the photon-baryon fluid.
  This makes it easier to fall into a potential
  well and harder to bounce to become a
  rarefaction.
• Baryon loading enhances the compressions and
  weakens the rarefactions, leading to an
  alternating height of the peaks.
• At earlier times the baryon-photon fluid
  contributes more to the total density of the
  universe than the CDM. The effects of
  baryon-photon self-gravity enhance the
  fluctuations on small scales.
• Since the fluid has pressure, it is hard to
  compress.
• Infall into potentials is slower than free-fall.
• Because the (over-)density cannot grow fast
  enough, the potential is forced to decay by the
  expansion of the universe.
• The photons are then left in a compressed state
  with no need to fight against the potential as
  they leave -- enhancing small-scale power.

Measuring the higher peaks constrains the matter
density!
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The high-z universe

• Planck will dramatically improve our knowledge of
  the physical conditions of the universe at
  z1000.
• The physical matter and baryon densities (in
  g/cm3), the acoustic scale and the distance to
  last scattering will be determined to sub-percent
  accuracy.
• Equality is also tightly constrained
• Know wg from Tcmb
• Know wr if standard neutrinos are only other
  species and having wm from the peaks gives zeq
• Extra species, or decaying components, are also
  tightly constrained by the behavior of the
  potentials during radiation domination.
  (Eisenstein White)

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Secondary science

• Planck enables numerous secondary science
  applications through its combination of high S/N
  and excellent frequency coverage.
• Thermal Sunyaev-Zeldovich effect
• Clusters of galaxies or first stars?
• Lensing of the CMB
• Probe of growth, features in P(k) and/or mn.
• ISW as a probe of low-z physics
• Dark energy fluctuations?

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The Thermal SZ effect
High signal to noise and angular resolution are
essential to studying higher order effects and
cross-correlating CMB maps with observations at
other wavelengths.
Input SZ simulation
WMAP 4yr
Planck 1yr
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The Planck SZ catalog

• Planck is not an ideal instrument for finding
  clusters using their SZ effect.
• For all but the most massive clusters
• Beam is too large
• Sensitivity is not high enough
• However Planck is an all-sky survey, and the SZ
  surface brightness is independent of redshift.
• A cluster that is large enough can be seen
  anywhere within the observable universe.
• Planck will find thousands of the most massive
  clusters.
• The most massive clusters are the rarest, but
  also some of the most interesting objects in
  cosmology.
• The Planck cluster catalog will be the best
  resource for studying the extreme limit of
  structure formation!

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An all-sky catalog of rich clusters
A simulation of the Planck cluster catalog, using
a simple peak finding method. This plot shows
clusters with Mgt8x1014 M0/h. Many lower mass
clusters are also found.
2 of sky simulated!
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The CMB prior

• With WMAP, and certainly after Planck, we will
  have very precise knowledge of the universe at
  z1000.
• We will have tightly constrained the physical
  densities of matter and baryons, the amplitude of
  the fluctuations in the linear phase over 3
  decades in length scale and the shape of the
  primordial power spectrum.
• Our knowledge of physical conditions and
  large-scale structure at z1000 will be better
  than our knowledge of such quantities at z0!
• One should not ignore this dramatic advance in
  our knowledge.
• Hold the high-z universe fixed
• Impose strong CMB priors on future
  measurements.

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Large-scale structure at z3

• Knowing equality and the baryon fraction enables
  us to predict the shape of the linear theory
  (matter) power spectrum extremely accurately in
  Mpc
• Note, not h-1 Mpc as would quote for local
  measures.
• Knowing wm and zeq fixes H(z) at high-z
• The amplitude of the fluctuations is well
  constrained by anisotropy measurements, up to the
  degeneracy with t.
• Conserved quantity is (roughly) dm e-t
• Unless dark energy is important at zgtgt1, we can
  evolve our fluctuations reliably from z1000 to
  z3 dma.

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The real-space z3 power spectrum
This enables us to constrain the high-z matter
power spectrum (with lengths measured in
meters!) Example using the WMAP 1yr data
constrains D2(k) to 7 near k0.01 up to the t
degeneracy.
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Making it to z0

• The uncertainty in structure formation thus comes
  from the extrapolation to z0 and to redshift
  space.
• Growth of fluctuations between z3 and z0
  depends on dark energy or massive neutrinos
  (vertical shifts).
• Conversion from physical distances (in Mpc) to
  local intervals (in h-1 Mpc) brings in a
  dependence on h or Wm (horizontal shifts).

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Conclusions

• Planck will provide a dramatic advance in our
  knowledge of primary and secondary CMB
  anisotropies.
• Testing inflation.
• Constraining the universe at z1000
• Dark energy
• An all sky-catalog of massive clusters of
  galaxies.
• The CMB centric view of structure formation.

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The End