presentation

Cosmic Microwave Background
the next frontier?
V(φ)
φ
Licia Verde
ICREA & ICC-UB
Barcelona
http://icc.ub.edu/~liciaverde
Some history
Discovery
1978 Nobel
Two engineers for Bell Labs accidentally discovered the CMB radiation, as a uniform
glow across the sky in the radio part of the spectrum, in 1965. It is the blackbody
emission of hot, dense gas (T~3000 K, λmax~1000 nm) red-shifted by a factor of 1000,
to a peak wavelength of 1 mm and T~3K.
“The primordial fireball”
Support to the hot
big bang theory
“Well boys, we have
been scooped”
Some history
COBE (1992): Nobel prize in Physics in 2006
Mather: for measuring the
CMB to be a Blackbody
Smoot: for measuring the
tiny temperature variations
Density fluctuations: seeds of
cosmological structures
"These measurements... marked the inception of cosmology as a precise science"
Perturbations: Some history
The era of precision cosmology:
LCDM: the “standard” model for cosmology
Few parameters describe the Universe composition and evolution
Homogenous background
Perturbations
Some history
Fast-forward 15 years:
TOCO (1998 ground-based)
MAXIMA (2000 balloon)
BOOMERANG* (1998 & 2003, balloon)
ARCHEOPS*
(2002, balloon)
DASI* (2001, ground, interferometer)
CBI (2002, ground, interferometer)
ACBAR (2002, ground, array)
VSA (2002, ground, interferometer)
CBI
ACBAR
Some history
WMAP (2003)
Detailed statistical
properties of these ripples
tell us a lot about the
Universe
Nolta et al 08
State of the art: temperature
ACT
The future is here
Planck satellite successfully launched in May!
“PR” image
There’s more!
Polarization
WMAP (2006)
First detected by DASI in 2002
What next?
a) Beyond primary anisotropies
Use the CMB as a backlight to illuminate the growth
of cosmological structure.
• First galaxies
• Universe is reionized
• Ostriker-Vishniac/KSZ
• weak lensing
•Sunyaev-Zel’dovich (SZ) clusters
• Diffuse thermal SZ
•Kinetic SZ
•Rees-sciama/ISW
Watch this space because experiments like e.g.,
South Pole Telescope or Atacama Cosmology Telescope
are releasing data these days
What next?
b)Polarization, the next frontier
Why measure CMB Polarization?
Directly measures dynamics in early universe
So far:
Critical test of the underlying theoretical framework for cosmology
Future: “How did the Universe begin?”
Improve cosmological constraints
Eventually, perhaps, test the theory of inflation.
Problems of the Hot BIG BANG model
Horizon problem
Flatness problem
Structure Problem
The inflationary solution
V(φ)
H ~ const
φ
Accelerated expansion…
Factor 10 26 in less than 10 -34 s
Solves cosmological problems (Horizon, flatness).
Cosmological perturbations arise from quantum fluctuations, evolve classically.
Guth (1981), Linde (1982), Albrecht & Steinhardt (1982), Sato (1981), Mukhanov & Chibisov
(1981), Hawking (1982), Guth & Pi (1982), Starobinsky (1982), J. Bardeen, P.J. Steinhardt, M.
Turner (1983), Mukhanov et al. 1992), Parker (1969), Birrell and Davies (1982)…
Perturbations: adiabatic
(
isocurvature
)
Photons
Neutrinos
Baryons(+electrons)
Dark matter
(dark energy negligible
early on)
Tensor
(gravitational waves)
Fig. From W. Hu.
Inflationary cosmology
Friedmann equations, a is scale factor
Single field slow roll inflation:
the simplest example
Inflate:
Sustain it
Process must terminate somehow
Restrictions in the form of the inflaton potential V:
SLOW ROLL PARAMETERS
Inflationary cosmology
Physical wavelength of fluctuations is stretched by expansion
The physical horizon is time dependent
Physical wavelengths grow faster than the horizon
Origin of structure
Quantum fluctuations get stretched to become classical
and “super-horizon” because of the accelerated expansion
But the spacing of the fluctuations
(their power as a function of scale)
depend on how fast they exited the horizon (H)
Which in turns depend on the inflaton potential
The shape of the primordial power spectrum
encloses information on the shape of the inflaton potential!
Primordial power spectrum=A kn
Amplitude of the power law
ln P(k)
slope
A (convention
dependent)
ln k
Equal power per log k, n=1, scale invariant
!
Slow roll predictions
ε∝V’/V
Other models, of course
CMB Consistent with Simplest Inflationary Models
• Flat universe:
Ωtot = 1.0052 ± 0.0064
(with SN and BAO)
Causal Seed model
(Durrer et al. 2002)
Primordial
Isocurvature i.c.
• Gaussianity: -9 < ƒNL < 111
• Power Spectrum spectral index
nearly scale-invariant:
ns = 0.97 ± 0.01
• Adiabatic initial conditions
WMAP
TE data
• Superhorizon fluctuations
(TE anticorrelations)
Still testing basic aspects of inflationary mechanism
rather than specific implementations
Primordial Adiabatic i.c.
Hu & Sujiyama 1995
Zaldarriaga & Harari 1995
Spergel & Zaldarriaga 1997
Peiris et al 2003
Generation of CMB polarization
• Temperature quadrupole at the surface of last
scatter generates polarization.
From Wayne Hu
Potential hill
Potential well
Polarization for density perturbation
• Radial (tangential) pattern around hot (cold) spots.
And it has been seen!
Komatsu, WMAP7yrs team (2010)
Theory
prediction
Observed
Large-scale TE anti correlation
Velocities
(hot to cold)
Density
mode
Hot due
to doppler
During decoupling
Gravity waves (tensor) are different…
Image from J. Rhul.
Image from J. Rhul.
E and B modes polarization
E polarization
from scalar and tensor modes
B polarization
only from tensor modes
Kamionkowski, Kosowsky, Stebbings 1997, Zaldarriga & Seljak 1997
Why polarization?
Temperature
(and E-modes)
Shape of the inflation potential
Energy Scale of Inflation (Height of the potential)
B-modes are needed!
Tensor to scalar ratio, r
Windows into the primordial Universe
Recombination
380000 yrs
Atomic physics/GR
Nucleosynthesis
3 minutes
Nuclear phyiscs
TeV energies
LHC
inflation
10 -30 s (?)
GUT?
Big BANG
Gravity Waves in the CMB
Inflation produces two types of perturbations: in the energy density ( as seen in
TT) and in the gravitational field (gravity waves). Unlike temperature anisotropy,
CMB polarization anisotropy can discriminate between scalar modes (density
perturbations) and tensor modes (gravity waves).
(r=tensor to scalar ratio)
Primordial B-mode anisotropy
–
–
Inflation-generated gravity waves (tensor modes) polarize CMB
(Kamionkowski & Kosowski 1998)
–
A “smoking gun” of inflation => holy grail of CMB measurements
–
At least an order of magnitude smaller than E-mode polarization
–
Great experimental challenge
–
Open debate on implications of possible experimental results
(Regular only)
Eric Hivon, IPAC
(Regular + Gravity waves)
Eric Hivon, IPAC
First Challenge
We live in a Galaxy
K Band (23 GHz)
Dominated by synchrotron; Note that polarization direction is
perpendicular to the magnetic field lines.
Ka Band (33 GHz)
Synchrotron decreases as n-3.2 from K to Ka band.
V Band (61 GHz)
The polarized foreground emission is also smallest in V band.
We can also see that noise is larger on the ecliptic plane.
W Band (94 GHz)
While synchrotron is the smallest in W, polarized dust (hard to
see by eye) may contaminate in W band more than in V band.
Relative Amplitudes of CMB power spectra
Foreground
τ = 0.16
τ = 0.10
τ = 0.16
r=0.1
τ = 0.10
τ = 0.16
τ = 0.10
r=0.001
First challenge
Foreground cleaning is crucial!
Frequency dependence
Templates
Etc…
Second challenge
1.
Weak lensing B-modes (life is never easy…)
–
Generated by weak lensing of the E-mode by large scale structure
(Zaldarriaga & Seljak 1998)
–
Subdominant on large scales, dominates on small scales
τ = 0.16
τ = 0.10
τ = 0.16
r=0.1
τ = 0.10
τ = 0.16
τ = 0.10
r=0.001
Third challenge
Considerations about detectors
Polarization-sensitive array of bolometers
Limited by
photon shot noise
(Good above ~100 GHz. E.g. Boomerang, DASI)
!Trms =
HEMT polarimeters
TCMB + Treceiver
!"!t
(good below ~ 100 GHz. E.g., WMAP)
Detector arrays needed to beat the noise limit per detector
Heavy!
Wide frequency range needed to keep foregrounds in check
Low l’s are Lensing-free
Systematic control
Large sky coverage
Stability
Space
Weigh
restrictions!
Current stage
WMAP(08)
DASI (02)
l
200
QUAD
400
600
800
Current stage
WMAP(08)
DASI (02)
l
200
400
600
800
QUAD
Fig from Pryke et al. 2009
Current constraints
WMAP5
Komatsu et al 08
The future
Ground-based, balloon borne experiments planned.
Survey of CMB polarization is a natural candidate for a space mission.
CMBPol mission concept study: probing inflation with CMB polarization
Bauman et al ’09: arXiv:0811.3919
Considerations in optimizing CMB polarization experiments to constrain
inflationary physics, LV, Peiris, Jimenez, ‘05; astro-ph/0506036
CMBPol mission concept study:prospects for polarized foreground removal
arXiv:0811.3915
The origin of the universe revealed through the polarization of the CMB
arXiv:0902.3796
Clues about high energy physics with the CMB polarization
Measurement of the amplitude of tensor modes fixes scalar field potential
and first derivative.
e.g. Liddle & Lyth (1993), Copeland et al. (1993), Liddle (1994)
r < 0.36
V 1/ 4 " 2.6 #1016 GeV
V 1/ 4 " 1.1#10$2 M Pl
Can take point of view that inflaton is a fundamental field, and use effective
field theory techniques to describe it. Effective potential can be expanded in nonrenormalizable operators suppressed by e.g. Planck
mass: e.g. Liddle & Lyth (1993),
!
Copeland et al. (1993), Liddle (1994)
p
*
$
'
1 2 2
"
V (" ) = V0 + m " + " 4 + # p &
)
2
% mPl (
p= 0
!
Lyth (1997)
For series expansion to be convergent and
EFT to be self-consistent, require φ << mPl.
Result used to argue that that very
small tensor modes are expected in a
realistic inflationary universe
Clues about high energy physics with the CMB polarization
Other criteria have been proposed…
Boyle, Steinhardt, Turok 2005
Clues about high-energy physics with the CMB polarization
Monte Carlo simulation of the inflationary flow equations.
"#
$ 6 r1/ 4
mPl
5 1015GeV
!
A “critical value”
What would it take?
Experimental forecasts including foreground subtraction uncertainties
(Verde, Peiris, Jimenez 2006, appendix of Baumann et al 2008)
From EPIC
mission concept study
Good foreground knowledge and some luck.
Putting it all together
Non -Gaussianity
Probes the interaction of the field(s) during inflation
Non-gaussianity is unobservable in many single field, slow roll models
IF
Single field only one quantum filed driving inflation and generating perturbations
Canonical kinetic energy speed propagation of fluctuations is speed of light
Slow roll field evolution slow compared to Hubble time during inflation
Initial bunch-Davies vacuum the quantum field was in the preferred
adiabatic vacuum state just before fluctuations generation
A detectable amount is created when any of these conditions is violated
Conclusions
CMB: there will be life after Planck
Precision cosmology: “from what to why”
CMB polarization is a window in the early universe
and into new physics at high energies
“How did the Universe begin?”
Challenging!
Obstacles to detecting B-mode polarization
•Fundamental complications:
•Level of primordial signal not guided at present by theory
•Signal not significantly contaminated by lensing only on largest
scales where cosmic variance is important
•Polarized FG emission on large scales likely dominate the signal at
all frequencies
•Practical complications:
•For signal to be detected in a reasonable timescale, instrumental
noise needs to be well below the photon noise limit for a single
detector ⇒ need multiple detectors
•Polarized FG not yet well known ⇒ FG subtraction uncertainties
seriously affect the goal
Guidance for B-mode polarization experiments
•Space-based:
•Can detect r=0.001 if FG can be subtracted at the 1% level, but
the main obstacle to detecting a small value of r<0.001 will come
from FG contamination.
•Can be optimized to access the low-l “reionization bump” constraints dependent on the value of the optical depth to
reionization.
•Balloon-borne:
•Has access to reionization bump, cheaper than going to space,
more adaptable/expandable than a space-mission.
•Future advances to ballooning technology: e.g. “stratellite”
airship combining the advantages of space-based and balloonborne experiments may be particularly attractive.
Combination of approaches?
Image from http://www.sanswire.com
Conclusions: Implications for Inflation
We can only test models with large field
variations (or not inflation)
Examples of models falling within the
“detectability” regime are:
•Chaotic inflation models realized in supergravity
theory where the potential has a shift symmetry
Linde (2005) and references within
•Extranatural/pseudonatural inflation, in which the
inflaton is an extra component of a gauge field in a
5D theory compactified in a circle Hill & Leibovich
(2002), Arkani-Hamed et al. (2003)
•Purely 4d theories need more sophisticated
structures in order to protect the flatness of the
potential from excessive radiative corrections; in
general do not predict significant tensor modes Kim
et al. (2005), Arkani-Hamed et al. (2003)
Important to investigate the possibility of constructing particle-physics
motivated inflationary models with (Δφ/mPl) ≥ 1 since these are likely to be
the only models that can be probed by realistic CMB experiments in the near
future.
Summary
Tev
3.2x10
1.7x10
9.7x10
13
13
12
12
5.5x10
3x10
12
END
Which is it?
V (! )
r
n
!
Etc…
V (! )
V (! )
!
!