and LargeScale Structure 1 Cora Dvorkin IAS Princeton Harvard Hubble fellow COSMO 2014 August 2014 Chicago Outline Dark Matter overview Effect of WIMP Dark Matter ID: 468600
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Slide1
Probing Dark Matter with the CMB and Large-Scale Structure
1
Cora Dvorkin IAS (Princeton) Harvard (Hubble fellow) COSMO 2014August 2014, ChicagoSlide2
Outline
Dark Matter overview.
Effect of WIMP Dark Matter Annihilation on the CMB: Homogeneous scenario. Inhomogeneous scenario: boosted electron perturbations (Non-Gaussian signal). • Other effects: enhanced matter temperature fluctuations;
key observable: 21 cm radiation field; CMB B-mode polarization.
Effect of
Dark Matter-baryon interactions on the CMB and the Large-Scale Structure.
2Slide3
3Evidence for Dark Matter
The cosmic microwave background
Galaxy rotation curves
Gravitational
lensing
Overwhelming evidence for Dark Matter:
Galactic scales
Cluster scales
Cosmic Microwave Background
multipole
moment
l
Power spectrumSlide4
4Looking for Dark Matter
off the beaten track
Where do Dark Matter interactions matter?Some well known avenues:Excess high energy cosmic/gamma rays;Missing energy at colliders;Nucleon recoil deep underground;…
Important to look for new processesSlide5
FINAL PRODUCTS
WIMP Dark Matter Annihilation
5Slide6
Standard Recombination
Effective Boltzmann equation for the free electron density:
6
Peebles,
ApJ
(1968)Z’eldovich and Sunyaev, JETP (1969)Slide7
Standard Recombination
Effective Boltzmann equation for the free electron density:
Recombination
rate
7
Peebles,
ApJ
(1968)
Z’eldovich
and
Sunyaev
, JETP (1969)Slide8
Standard Recombination
Effective Boltzmann equation for the free electron density:
Ionization rate
Recombination
rate
8
Peebles,
ApJ
(1968)
Z’eldovich
and
Sunyaev
, JETP (1969)Slide9
Effective Boltzmann equation for the free electron density:
DM Annihilation in Recombination
Ionization rate
Recombination
rate
Energy injected into the plasma per unit volume, per unit time:
(
Majorana
particle)
Chen and
Kamionkowski
(2004)
Padmanabhan
and
Finkbeiner
(2005)
9Slide10
Time scales
(Recombination, Ionization, Expansion)
10
C. Dvorkin, K. Blum, and M.
Zaldarriaga
, Phys. Rev. D (2013)z (redshift)
1/MpcSlide11
Free electron fraction evolution
11
xe (ionization fraction)z (redshift
)Slide12
Effect on the CMB Temperature
A higher ionization
suppresses the CMB temperature fluctuationsCurrent CMB constraints are
GeV
Complementary to direct detection searches, that are most sensitive to GeV, due to kinematical considerations.
Degeneracy:
12
Padmanabhan
and
Finkbeiner
(2005)
multipole
moment
lSlide13
• Screening of the observed spectrum at l>100.• Re-scattering of photon generates extra polarization at large scales.
A higher ionization enhances the
polarization fluctuationsat large scales13
Effect on the CMB Polarization
multipole
moment
lSlide14
14
Current and Future
Dark Matter Annihilation Constraintsfrom
the CMB
• Planck polarization data: coming this year.
• CMB “Stage IV” experiment is being planned now!
W. Wu, J.
Errard
, C. Dvorkin, C. L.
Kuo
, A. Lee, et al.,
ApJ
(2014)
Thermal
cross section
M.
Madhavacheril
, N.
Sehgal
, T.
Slatyer
, Phys. Rev. D (2014)Slide15
There are growing ionization modes that track the collapse of matter overdensities.k=0.04 Mpc
-1
Dark Matter AnnihilationInhomogeneous scenario
15
perturbation
perturbation
time [
Mpc
]
time [
Mpc
]
C. Dvorkin, K. Blum, and M.
Zaldarriaga
, Phys. Rev. D (2013)
k
=0.04 Mpc
-1
k
=0.3 Mpc
-1Slide16
Order of magnitude boost!
16
C. Dvorkin, K. Blum, and M. Zaldarriaga
, Phys. Rev. D (2013)
electron perturbation
wave number k [1/Mpc]
Comparison
to standard first order electron perturbationsSlide17
17
Order of magnitude boost!
Comparison
to standard first order electron perturbations
electron perturbation
wave number
k
[1/Mpc]
C. Dvorkin, K. Blum, and M.
Zaldarriaga
, Phys. Rev. D (2013)Slide18
18
Can we observe electron density perturbations in the CMB?
C. Dvorkin, K. Blum, and M.
Zaldarriaga
, Phys. Rev. D (2013)CMB Bispectrum: probe of electron density perturbations.
• Signal-to-noise 0.5 for Planck;
polarization will have
more information (work in progress).
• The main boost in the electron perturbations by DM
annihilation occurs on small scales,
l
>3000 (challenging to
observe in
temperature)
.
Slide19
19
Enhanced Matter Temperature fluctuations
There should be more information in the 21 cm radiation field (future work).
wave number
k
[1/Mpc]Matter temperature fluctuationsCurrent and future 21 cm experiments:
LOFAR, MWA, PAPER,
SKA, etc, etc..Slide20
20
Beyond the WIMP paradigm
• It has been pointed out that Dark Matter self-interactions and Dark Matter-Baryon interactions can significantly affect small-scale structure. • Baryon processes such as star formation, supernova feedback, gas accretion, etc. can have important effects, but these processes are partially understood theoretically and poorly constrained observationally.
Spergel
and Steinhardt (2000);
Wandelt et al. (2000)Slide21
21Goal: to use observational probes of the CMB and matter fluctuations (where the theory is under better control) to know how much interaction between baryons and
Dark Matter can occur today.
Dark Matter-Baryon Interactions
C. Dvorkin, K. Blum and M.
Kamionkowski
, Phys. Rev. D (2013)Slide22
22
Dark Matter-Baryon Interactions
with
Dark Matter-baryon momentum exchange rate:
for
for
C. Dvorkin, K. Blum and M.
Kamionkowski
, Phys. Rev. D (2013)Slide23
23
Effect
on the Matter Power SpectrumC. Dvorkin, K. Blum and M. Kamionkowski, Phys. Rev. D (2013)
wave number
k
[h/Mpc
]
Matter Power Spectrum
P(k
) [(h
-1
Mpc)
3
]Slide24
24
Lyman-alpha
Effect on
the Matter Power Spectrum
C. Dvorkin, K. Blum and M.
Kamionkowski, Phys. Rev. D (2013)
wave number
k
[
h/Mpc
]
Matter Power Spectrum
P(k
) [(h
-1
Mpc)
3
]Slide25
25
Constraining Dark Matter-Baryon Scattering with Cosmology
All the curves ( ) are normalized to satisfy a mean free path of 1
Mpc
in a system like the Milky Way,with ,and .
C. Dvorkin, K. Blum and M.
Kamionkowski
, Phys. Rev. D (2013)
z (
redshift
)
(momentum exchange rate)/
(
comoving
Hubble expansion)Slide26
26
Minimal mean free path for baryons scattering on Dark Matter in the Milky Way
A baryon in the halo of a galaxy like our Milky Way does not scatter from Dark Matter particles during the age of the Universe.
C. Dvorkin, K. Blum and M.
Kamionkowski
, Phys. Rev. D (2013)
Mean free path:
(
CMB data
: from
Planck
;
Ly-alpha data
: from the
Sloan Digital Sky Survey
)Slide27
Conclusions
We will be able to put strong constraints on Dark Matter Annihilation with
future CMB observations (currently complementary to direct detection constraints). WIMP Dark matter annihilation leads to growing ionization modes that track the collapse of dark matter overdensities (boosted by 1 to 2 orders of
magnitude at small scales relative to standard model).
Electron perturbations source CMB Non-
Gaussianities at recombination. Enhanced matter temperature fluctuations at late times (natural observational tool: 21 cm radiation – future work).
Using CMB data from Planck + Ly-alpha forest measurements from
the Sloan Digital Sky Survey, we conclude that a baryon in the halo of a Galaxy
like our Milky Way does not scatter from Dark Matter particles during the age
of the Universe.
27Slide28
Can we observe electron density perturbations in the CMB?
CMB
Bispectrum: probe of electron density perturbations • From perturbed visibility: anisotropic optical depth.
The first and second order anisotropies today are given by the line of sight
solutions to the Boltzmann equation:
28
Seljak
and
Zaldarriaga
(1996)Slide29
Can we observe electron density perturbations in the CMB?
CMB
Bispectrum: probe of electron density perturbations
New anisotropies generated by electron perturbations:
• From perturbed visibility: anisotropic optical depth.
29Slide30
The main boost in the electron perturbations by DM annihilation occurs on small scales,
l>3000 (challenging to observe).
at peak visibility
at half-maximum visibility
Signal-to-noise 0.5 for Planck;
polarization will have more information (work in progress).
30
Can we observe electron density perturbations in the CMB?
C. Dvorkin, K. Blum, and M.
Zaldarriaga
, Phys. Rev. D (2013)
multipole
moment
l
multipole
moment
l
New anisotropies “
g
l
”
New anisotropies “
g
l
”Slide31
• Solve the perturbed Boltzmann equation up to second order in the tight coupling limit ( ) and identify the physical processes:
31
Perturbed Harmonic Oscillator
C. Dvorkin, K. Blum, and M.
Zaldarriaga
, in preparation
Silk damping
Sound speed
• Solution given by
WKB’s
Green function.Slide32
32
Imprints
on the CMB Power Spectrumfrom Dark Matter-Baryon scatteringC. Dvorkin, K. Blum and M.
Kamionkowski
, Phys. Rev. D (2013)
multipole
moment
l