Dan Hooper

1
Dark Matter Annihilations and the WMAP Haze

• Dan Hooper
• Particle Astrophysics Center
• Fermi National Accelerator Laboratory
• dhooper_at_fnal.gov

Fermilab September 10, 2007
2
Dark Matter

• Evidence from a wide range of astrophysical
  observations including rotation curves, CMB,
  lensing, clusters, BBN, SN1a, large scale
  structure
• Each observes dark matter through its
  gravitational influence
• Still no observations of dark matters
  electroweak interactions (or other
  non-gravitational interactions)

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
3
Dark Matter

• Evidence from a wide range of astrophysical
  observations including rotation curves, CMB,
  lensing, clusters, BBN, SN1a, large scale
  structure
• Each observes dark matter through its
  gravitational influence
• Still no observations of dark matters
  electroweak interactions (or other
  non-gravitational interactions)
• The particle identity of dark matter remains
  unknown

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
4
The Thermal Abundance of Weakly Interacting
Massive Particles

• T gtgt m?, ?s in thermal equilibrium
• T lt m?, number density of ?s become Boltzmann
  suppressed
• T m?/20, Hubble expansion dominates over
  annihilations, freeze-out occurs
• Precise temperature at which freeze-out occurs,
  and the density which results depends on the
  WIMPs annihilation cross section

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
5
The Weak Scale and Weakly Interacting Massive
Particles

• As a result of the thermal freeze-out process, a
  relic density of WIMPs is left behind ? h2 xF
  / lt?vgt
• For a particle with a GeV-TeV mass, to obtain a
  thermal abundance equal to the observed dark
  matter density, we need an annihilation cross
  section of lt?vgt pb
• Generic weak interaction yields
• lt?vgt ?2 (100 GeV)-2 pb

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
6
The Weak Scale and Weakly Interacting Massive
Particles

• As a result of the thermal freeze-out process, a
  relic density of WIMPs is left behind ? h2 xF
  / lt?vgt
• For a particle with a GeV-TeV mass, to obtain a
  thermal abundance equal to the observed dark
  matter density, we need an annihilation cross
  section of lt?vgt pb
• Generic weak interaction yields
• lt?vgt ?2 (100 GeV)-2 pb

Numerical coincidence? Or an indication that
dark matter originates from EW physics?
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
7
Astrophysical Probes of Particle Dark Matter
Direct Detection -Momentum transfer to
detector through elastic scattering
Indirect Detection -Observation of
annihilation products (?, ?, e, p, etc.)
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
8
Indirect Detection of Dark Matter
?

• WIMP Annihilation Typical final states
  include heavy fermions, gauge or Higgs bosons

?
W-
W
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
9
Indirect Detection of Dark Matter
?

• WIMP Annihilation Typical final states
  include heavy fermions, gauge or Higgs bosons
• 2) Fragmentation/Decay Annihilation
  products decay and/or fragment into some
  combination of electrons, protons, deuterium,
  neutrinos and gamma rays

?
W-
q
W
q
?
e
?0
p
?
?
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
10
Indirect Detection of Dark Matter
?

• WIMP Annihilation Typical final states
  include heavy fermions, gauge or Higgs bosons
• 2) Fragmentation/Decay Annihilation
  products decay and/or fragment into some
  combination of electrons, protons, deuterium,
  neutrinos and gamma rays
• 3) Synchrotron and Inverse Compton Relativistic
  electrons up-scatter starlight to MeV-GeV
  energies, and emit synchrotron photons via
  interactions with magnetic fields

?
W-
q
W
q
?
e
?0
p
?
?
?
e
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
11
Indirect Detection of Dark Matter
Neutrinos from annihilations
in the core of the Sun Gamma Rays from
annihilations in the galactic
halo, near the galactic center, in dwarf
galaxies, etc. Positrons/Antiprotons from
annihilations throughout the galactic
halo Synchrotron Radiation from electron/positron
interactions with the magnetic fields of the
inner galaxy
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
12
Indirect Detection With Synchtrotron

• Electrons/positrons produced in dark
  matter annihilations inverse Compton scatter
  with starlight and emit synchrotron
  photons as they propagate through the galactic
  magnetic fields
• For electroweak-scale dark matter, the resulting
  synchrotron radiation falls within the frequency
  range of WMAP

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
13
WMAP As A Synchrotron Telescope

• In addition to CMB photons, WMAP data is
  contaminated by a number of galactic
  foregrounds that must be accurately subtracted
• The WMAP frequency range is well suited to
  minimize the impact of foregrounds
• Substantial challenges are involved in
  identifying and removing foregrounds

Thermal Dust
Soft Synchrotron
WMAP
Free-Free
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
14
WMAP Foregrounds

• Soft Synchrotron - From SN shocks morphology
  traced by the 408 MHz Haslam map
• Free-Free - Hot gas electron/ion thermal
  Bremsstrahlung morphology traced by the H?
  recombination line map (Finkbeiner, 2003)
• Thermal/Spinning Dust -Emission
  from vibrating and spinning dust grains
  morphology traced by the SFD98 dust map
  (Schlegel et al.) and the 94 GHz
  Finkbeiner map

Thermal Dust
Soft Synchrotron
WMAP
Free-Free
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
15
Synchrotron



Free-free


T S Dust
WMAP

CMB
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
16
Synchrotron



Free-free


T S Dust
WMAP

Well, actually No
CMB
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
17
Synchrotron



Free-free
_


T S Dust
WMAP

CMB
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
18
The WMAP Haze
22 GHz
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
19
The WMAP Haze
22 GHz
After known foregrounds are subtracted, an excess
appears in the residual maps within the inner
20? around the Galactic Center
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
20
The WMAP Haze
22 GHz

• Initially interpreted as likely thermal
  bremsstrahlung (free-free emission)
  from hot gas (104-106 K)
• This interpretation has since been ruled out
  by the lack of a corresponding H?
  recombination (X-ray) line
• Appears to be hard synchrotron emission from a
  new population of energetic electrons/positrons
  in the inner galaxy
• -Too hard to be supernovae shocks
• -Too extended to be a singular event (GRB,
  etc.)
• Very Difficult to explain astrophysically

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
21
Dark Matter and the WMAP Haze

• In 2004, Doug Finkbeiner suggested that the
  WMAP Haze could be synchtrotron from
  electrons/positrons produced in dark
  matter annihilations in the inner galaxy
  (astro-ph/0409027)
• In particular, he noted that
• 1) Assuming an NFW profile, a WIMP mass of 100
  GeV and an annihilation cross section of 3x10-26
  cm3/s, the total power in dark matter
  annihilations in the inner 3 kpc of the Milky Way
  is 1.2x1039 GeV/sec
• 2) The total power of the WMAP Haze is between
  0.7x1039 and 3x1039 GeV/sec

22 GHz
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
22
Dark Matter and the WMAP Haze

• In 2004, Doug Finkbeiner suggested that the
  WMAP Haze could be synchtrotron from
  electrons/positrons produced in dark
  matter annihilations in the inner galaxy
  (astro-ph/0409027)
• In particular, he noted that
• 1) Assuming an NFW profile, a WIMP mass of 100
  GeV and an annihilation cross section of 3x10-26
  cm3/s, the total power in dark matter
  annihilations in the inner 2 kpc of the Milky Way
  is 1.2x1039 GeV/sec
• 2) The total power of the WMAP Haze is between
  0.7x1039 and 3x1039 GeV/sec

22 GHz
Coincidence?
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
23
Electron-Positron Diffusion

• When electrons/positrons are produced in dark
  matter annihilations, they travel through the
  galaxys tangled magnetic fields, losing energy
  via synchtrotron and inverse Compton
• Resulting spectrum can be calculated by solving
  the diffusion-loss equation
• For 10-50 GeV e/- in the inner
  galaxy, leads to 0.1-1 kpc diffusion
  (1-10?)

Source Term
Diffusion Constant
Energy Loss Rate
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
24
Fitting The Haze To The Dark Matter Halo Profile

• When the effects of diffusion
  are accounted for, we find that an
  NFW halo profile (? ? R-1) under produces
  the WMAP haze at small angles
• Angular distribution of the haze matches that
  found for a cusped halo profile, with ? ? R-1.2
• Although the precise result of this fit depends
  on the diffusion parameters adopted (magnetic
  fields, starlight density, etc.), the approximate
  result (slope of -1.1 to -1.3) is fairly robust

?(R) ? R-1.2


Significant systematic errors
?(R) ? R-1 (NFW)
Hooper, G. Dobler and D. Finkbeiner,
arXiv0705.3655
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
25
Dark Matter Annihilation Radiation and the
Spectrum of the WMAP Haze

• To some extent, the Haze is seen in all five of
  WMAPs frequency bands (although significant
  systematic errors make the high frequency
  information somewhat unreliable)
• By comparing the ratio of the intensities at 22
  and 33 GHz from the inner galaxy, the responsible
  electron/positron spectrum can be constrained,
  and along with it the dark matter mass and
  annihilation modes

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
(Caution statistical errors only)
26
Dark Matter Annihilation Radiation and the
Spectrum of the WMAP Haze

• The WMAP data are consistent with a ratio of
  intensities at 22 and 33 GHz within the
  range of 1.0-1.4
• For WIMPs annihilating to gauge bosons or
  leptons, a WIMP with a mass in the
  range of 50 GeV to multi-TeV
  is acceptable
• For a WIMP annihilating to b quarks, 200 GeV
  to multi-TeV is favored

bb
WW, ZZ
??
ee
??
Hooper, G. Dobler and D. Finkbeiner,
arXiv0705.3655
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
27
The Dark Matter Annihilation Cross Section

• For a given annihilation mode, diffusion
  parameters and halo profile, we can calculate the
  annihilation cross section needed
  to normalize the observed
  intensity of the WMAP Haze
• For a typical 100-1000 GeV WIMP, the annihilation
  cross section needed is within a factor of 2-3 of
  the value needed to generate the density of dark
  matter thermally (3x10-26 cm3/s) No boost
  factors are required!

bb
WW, ZZ
??
??
ee
Hooper, G. Dobler and D. Finkbeiner,
arXiv0705.3655
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
28
Testing the Haze-Dark Matter Connection With
Gamma-Rays

• Advantages of Gamma-Rays
• Propagate undeflected (point sources possible,
  angular information)
• Propagate without energy loss (spectral
  information)
• Rapid development in both space (GLAST) and
  ground-based (HESS, MAGIC, VERITAS)
  technologies

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
29
Gamma-Rays From The Galactic Center

• Simulations predict that the GC contains very
  high densities of dark matter (and high
  annihilation rates)
• Long considered likely to be the brightest dark
  matter annihilation region in the sky
• HESS, MAGIC, WHIPPLE and CANGAROO each claim
  positive detection of TeV gamma-rays
• Evidence for dark matter, or other astrophysics?

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
30
Gamma-Rays From The Galactic Center

• Spectrum as measured by HESS extends to at least
  10TeV
• Consistent with a constant power-law spectrum
• To fit with dark matter would require a very
  heavy particle (15-30 TeV) - Far too heavy for
  a neutralino
• A very heavy dark matter candidate
  also fails to match the spectral
  shape reported by HESS

Power-Law Fit
Heavy DM
HESS Collaboration, PRL, astro-ph/0610509
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
31
Gamma-Rays From The Galactic Center

• The GC is a region rich in extreme astrophysical
  objects
• Particle acceleration associated with
  supermassive black hole?
• Aharonian and Neronov (astro-ph/0408303),
• Atoyan and Dermer (astro-ph/0410243)
• This astrophysical source represents a very
  daunting background for future dark matter
  searches to compete with

Hooper, Perez, Silk, Ferrer and Sarkar, JCAP,
astro-ph/0404205
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
32
Gamma-Rays From The Galactic Center

• Prospects for GLAST and other future gamma-ray
  experiments are reduced as a result of this new
  background
• Range of annihilation rates observable with
  GLAST is reduced considerably
• Other potential sources of dark matter
  annihilation radiation become more
  interesting (dwarf spheroidal galaxies,
  the diffuse background, etc.)

Excluded by HESS
Excluded by EGRET
GLAST Reach
GLAST Reach (neglecting BG)
Hooper and G. Zaharijas, PRD, hep-ph/0603540
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
33
Gamma-Ray Signals of The Dark Matter-WMAP Haze
Connection

• The observed properties of the Haze can be used
  to calculate the intensity and angular
  distribution of gamma rays from dark matter
  annihilations from the inner galaxy
• An angular distribution and intensity similar to
  this prediction would provide an important
  confirmation of the dark matter origin of the
  haze Conversely the absence of such a signal
  would refute the hypothesis (highly falsifiable!)

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
34
Gamma-Ray Signals of The WMAP Haze
Projected GLAST Error Bars
Inner 0.1?
0.3?-0.5?
background
Annihilations to heavy fermions or gauge
bosons and easily identifiable by GLAST
annihilations to muons/electrons are unlikley to
be observable
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
Dobler, Finkbeiner, Hooper, Zaharijas, in
preparation
35
The WMAP Haze In Light Of Planck

• Planck (launch in 2008) will represent a
  major step forward from WMAP
• Improved frequency coverage
• Much greater polarization information
  (synchrotron emission is highly polarized)
• Improved angular resolution
• At frequencies above 100 GHz, all foregrounds
  other than emission from thermal dust are
  negligible subtracting one
  foreground rather than the several
  (3 or 4) required at WMAP frequencies will
  enable for a much more robust confirmation of the
  synchrotron origin of the Haze
• Systematic uncertainties are expected to be
  reduced by more than an order of magnitude
  relative to WMAP

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
36
What About Other Claims of Evidence For Dark
Matter Annihilation?

• The HEAT positron excess
• 511 keV emission from the galactic bulge
• EGRETs galactic gamma ray spectrum
• EGRETs extragalactic gamma ray spectrum

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
37
The HEAT Positron Excess

• In its 1994-95, 2000 flights, the HEAT
  balloon-based cosmic ray detector observed an
  excess of positrons relative to electrons in
  the 7-30 GeV range
• Measurements from AMS-01 add some support
• Combined statistical significance of several
  (4-5) sigma, neglecting (likely important, but
  difficult to evaluate) systematic uncertainties

E. Baltz and J. Edsjo, PRD, astro-ph/9808243
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
38
The HEAT Positron Excess

• Strengths
• Fit to data can be easily improved if dark
  matter component is included
• Weaknesses
• Messy astrophysics
• Requires annihilation boost of 50 or more
  (possible, but unlikely), or non-thermal dark
  matter production
• Prospects
• PAMELA data (August?) should clearly confirm or
  refute this signal, and measure the spectrum up
  to much higher energies

PAMELA
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
39
511 keV Emission from the Galactic Bulge

• INTEGRAL/SPI observed bright 511 keV emission
  from the bulge of the Milky Way (1.3 x 1043
  positrons injected per second)
• Gaussian, spherically symmetric morphology
  (FWHM of 8)
• The source of these positrons remains unknown

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
40
511 keV Emission from the Galactic Bulge

• Type Ia supernovae are unable to generate the
  observed injection rate (too few escape)
• Hypernovae (type Ic SNe) or gamma ray bursts
  could potentially generate enough positrons if
  high estimates for rates are considered
• Even if the injection rate is sufficient, a
  mechanism is required to transport from disk to
  bulge - appears to be somewhat difficult

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
41
511 keV Emission and MeV Dark Matter

• The INTEGRAL morphology matches well that which
  would be generated through the annihilation
  (or decay) of dark matter
• 1-10 MeV dark matter particles annihilating to
  ee- could simultaneously generate the measured
  dark matter relic abundance, and the observed 511
  keV emission
• (Boehm, Hooper, Silk, Casse, Paul, PRL,
  astro-ph/0309686)

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
42
511 keV Emission and MeV Dark Matter

• Strengths
• Challenging to explain 511 signal with non-exotic
  astrophysics
• Weaknesses
• Somewhat difficult to construct a viable particle
  physics model with an MeV WIMP
• Prospects
• No clear path to confirmation or exclusion of the
  MeV dark matter hypothesis (perhaps 511 emission
  from dwarf galaxies?)

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
43
EGRETs Galactic Gamma Ray Spectrum

• EGRET observed an excess of gamma rays above 1
  GeV, compared to the the most simple galactic
  cosmic ray models
• Coud be the product of a 50-100 GeV WIMP
  (W. de Boer et al, PLB, hep-ph/0511154
  Astron.Astrophys, astro-ph/0508617
  astro-ph/0408272)

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
44
EGRETs Galactic Gamma Ray Spectrum

• The same dark matter annihilation spectrum can
  fit the shape of the GeV excess in all regions of
  the sky
• To normalize the intensity of each region,
  however, requires a departure from a
  simple halo profile
• De Boer, et al. introduce two rings of dark
  matter near the galactic plane at
  4 and 14 kpc from galactic center (8x1010
  M? tidally disrupted dwarf galaxy? motivated
  by rotation curves)

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
(W. de Boer et al, A.A., astro-ph/0508617)
45
EGRETs Galactic Gamma Ray Spectrum

• With a standard treatment of cosmic ray
  diffusion, far too many antiprotons are produced
  in this scenario
• To reconcile, anisotropic diffusion, strong
  convection away from (and outside of) the disk
  and local spatial variations are required

Prediced in de Boer model
Prediction from standard secondary cosmic ray
production

(Bergstrom, Edsjo, Gustafsson and Salati, JCAP,
astro-ph/0602632)
Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
46
EGRETs Galactic Gamma Ray Spectrum

• Strengths
• Consistent with a neutralino or other
  EW-scale WIMP
• Similar spectral shape over sky
• Weaknesses
• Non-standard dark matter distribution is
  needed (two rings)
• Conflict with antiprotons unless
  non-standard comic ray diffusion is invoked
• The GeV excess can plausbily be reduced or
  eliminated without dark matter by modifying the
  diffusion model
• Prospects GLAST will clear up these questions
  considerably

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
47
EGRETs Extragalactic Gamma Ray Spectrum

• EGRET has also detected a diffuse, extragalactic
  gamma ray signal, which becomes more intense
  above 1 GeV
• Integrated signal from dark matter annihilations
  throughout the universe could produce a
  potentially observable signal (Ullio,
  Bergstrom,Edsjo 2002)
• Intensity depends critically on dark
  matter distribution - cuspy halos and
  substructure are required
• The EGRET extragalactic diffuse spectrum
  can be fit by annihilations from a 500 GeV
  neutralino (or other WIMP)

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
Elsasser and Mannheim, PRL, astro-ph/0405235
48
EGRETs Extragalactic Gamma Ray Spectrum

• Strengths
• Consistent with a (somewhat heavy) neutralino or
  other WIMP
• Weaknesses
• Not a particularly distinctive signal,
  could easily be astrophysical
• High annihilation rate needed either large
  degree of very cusped substructure, or a
  non-thermal WIMP
• Signal from our galactic center would have
  been seen, unless cusp is removed by
  tidal effects (S. Ando, PRL, astro-ph/0503006)
• Prospects GLAST will clearly resolve

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
49
Signal Required Particle Physics Required Astrophysics
WMAP Haze 100 GeV to multi-TeV WIMP, 3x10-26 cm3/s annihilation cross section Cusped halo profile, standard diffusion, no boost factors
HEAT Positron Excess 50-1000 GeV WIMP Either large (non-thermal) annihilation cross section OR Large boost factor (50 or more)
INTEGRAL 511 keV Emission MeV particle, p-wave annihilator with 3x10-26 cm3/s annihilation cross section Mildly cusped halo profile
EGRET Diffuse Galactic 50-300 GeV WIMP Either large (non-thermal) annihilation cross section OR Large boost factors two massive rings of dark matter in the galactic plane non-standard, highly convective diffusion model
EGRET Diffuse Extragalactic 500 GeV WIMP Either large (non-thermal) annihilation cross section OR Large boost factors/highly cusped profiles Conflict with Milky Way unless Galactic Center is exceptional

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
50
Signal Required Particle Physics Required Astrophysics
WMAP Haze 100 GeV to multi-TeV WIMP, 3x10-26 cm3/s annihilation cross section Cusped halo profile, standard diffusion, no boost factors
HEAT Positron Excess 50-1000 GeV WIMP Either large (non-thermal) annihilation cross section OR Large boost factor (50 or more)
INTEGRAL 511 keV Emission MeV particle, p-wave annihilator with 3x10-26 cm3/s annihilation cross section Mildly cusped halo profile
EGRET Diffuse Galactic 50-300 GeV WIMP Either large (non-thermal) annihilation cross section OR Large boost factors two massive rings of dark matter in the galactic plane non-standard, highly convective diffusion model
EGRET Diffuse Extragalactic 500 GeV WIMP Either large (non-thermal) annihilation cross section OR Large boost factors/highly cusped profiles Conflict with Milky Way unless Galactic Center is exceptional

Dan Hooper - Dark Matter Annihilations
and the WMAP Haze
51
Conclusions

• WMAP data, after the subtraction of known
  foregrounds, contains an excess from the region
  around the center of the Milky Way - The WMAP
  Haze
• Consistent with synchrotron emission from
  energetic electrons/positrons from
  dark matter annihilations with
• -A cusped halo profile
• -A 100 GeV to multi-TeV WIMP
• -An annihilation cross section within a factor
  of 2-3 of the value required of a thermal relic
  (3x10-26 cm3/s)

52
Conclusions

• We may very well be looking at the first
  detection of supersymmetry or other TeV scale
  physics beyond the Standard Model
• Future measurements by GLAST and PLANCK will
  clarify the nature of the WMAP Haze
• The dark matter - WMAP Haze connection is a
  clearly falsifiable/verifiable hypothesis
• With GLAST and Planck, in a couple of years,
  we will know one way or the other