Stefano Profumo
UC Santa Cruz
Santa Cruz Institute for Particle Physics
T.A.S.C. [Theoretical Astrophysics in Santa Cruz]
New Physics with ACTs
in the Fermi Era
TeV Particle Astrophysics 2009
SLAC National Accelerator Laboratory, Menlo Park, CA,
July 13-17, 2009
Annihilation debris: an unavoidable
consequence of thermal WIMPs
Gamma Rays
1. “Primary”
• Hadronization, p0 gg
• Final State Radition (e.g. L+L- g)
(included in e.g. DMFIT)
• “Intermediate State” Radiation
(model-dependent, incl. in DSv5)
• Loop-suppressed radiative
annihilation modes (gg, Zg, hg, …)
Credit: Fermilab Website
WIMP annihilation also produces stable Electrons and Positrons,
which diffuse and loose energy
Inverse Compton off CMB and starlight photons,
Bremsstrahlung and Synchrotron emission
produce radiation from radio to gamma-ray frequencies
1. Source Term
2. Transport Equation

2

dN e ( E )
 DM
( x)
Q( E , x ) 
  v rel
2
mDM
dE
 dn   
 dne 

 dne

   D( E , x ) e  
b
(
E
,
x
)

Q
(
E
,
x
)


t dE
dE  E 
dE 

3. Compute the Signals
(IC off CMB/starlight, Synchrotron emission,…)

n ( E, x )
EQ
e
Annihilation debris: an unavoidable
consequence of thermal WIMPs
Gamma Rays
1. “Primary”
2. “Secondary”
• Inverse Compton (e+ge+g)
(where g from CMB, starlight, IRB…)
• Bremsstrahlung
• Synchrotron (for large enough B)
Credit: Fermilab Website
The multi-wavelength spectrum expected from a
41 GeV “bino” annihilating in the Coma cluster
“Environment”-dependent
(B, gas density, diffusion)
Colafrancesco, Profumo and Ullio (2005)
Set by the
DM particle
mass scale
What is “magic” about gamma-ray telescopes
for the search for dark matter?
W~m
 ~ m2/mZ4
W ~ 1/ ~ m-2
 ~ m-2
W ~ m2
They probe the energy range where
the thermal cold DM mass scale is
Baltz (2004)
What is “magic” about gamma-ray telescopes
for the search for dark matter?
Gamma-Ray
“Debris”
Secondary & Low-E
Primary Radiation
WIMP Mass
Range
Non-thermal
Production
What is “magic” about gamma-ray telescopes
for the search for dark matter?
an “old”
Morselli plot
Secondary & Low-E
Primary Radiation
WIMP Mass
Range
Non-thermal
Production
Role of ACT’s in
the multi-frequency
siege to dark matter
in the Fermi Era
4. Cosmic Ray
Electrons/
Positrons
1. Dwarf
Galaxies
2. Galaxy
Clusters
3. Galactic
Center
1. Dwarfs: a lesson from CACTUS
Solar Array ACT located
at Solar Two,
Daggett (CA), operated by
UC Davis in ’04-’05
Observed PSR/SNR
(Crab, Geminga),
AGN (Mk421, 501)
and dSph Draco
Reported GR excess from Draco, later attributed to
problems with noise assisted trigger threshold connected to starlight
dSph are DM dominated and GR-quiet objects:
the usual suspect, DM interpretation of the excess
L.Bergstrom & D.Hooper, hep-ph/0512317 and S.Profumo & M.Kamionkowski, astro-ph/0601249
Excess Counts !!!
1. Dwarfs: a lesson from CACTUS
An important lesson: dSph are ideal targets for indirect DM searches
Moreover: ACTs are complementary to satellite-based GR telescopes
[EGRET didn’t detect Draco]
S.Profumo & M.Kamionkowski, astro-ph/0601249
1. Dwarfs: general features of Fermi vs ACT
dark matter search sensitivity
CACTUS signal  huge cross section
ACT Limitation: low-energy threshold
ACT Asset: Great sensitivity to final states producing hard GR spectrum!
1. Dwarfs: Fermi results (T. Jeltema’s talk)
Preliminary
* Asset of Fermi: sensitivity to
Inverse Compton Gamma Rays!
* Large Uncertainties on Diffusion
in small extragalactic systems!
1. Dwarfs: Comparing MAGIC and Fermi
Preliminary
* Even without IC, the Fermi survey-mode
gives it an edge over ACTs
* Comparable sensitivities for m~1 TeV,
~100h ACT obs. time
1. Dwarfs: prospects for ACTs in the Fermi era
Is it worth it for
ACTs to observe
local dSph to search
for DM in the
Fermi era?
YES: one example:
DM model that fits
positron excess
TeV particle mm
Large Diffusion in dSph
makes ACT much
better than Fermi!
1. Dwarfs: prospects for ACTs in the Fermi era
Another example:
Standard Neutralinotype DM particle,
negligible IC
m~1 TeV, comparable
sensitivities for
Fermi vs ACTs
m~5 TeV, ACTs can
outperform Fermi
2. Clusters: a new gamma-ray source class?
* Largest bound dark matter structures
* Non-thermal activity detected as synchrotron radio emission
* Likely source of gamma rays from
hadronic or leptonic primary cosmic rays
* Not conclusively detected so far in gamma rays
* Excess hard X radiation detected in a few cases
Galaxy Cluster Abell 1689 Warps Space Credit: N. Benitez (JHU)
2. Clusters: non-thermal activity from cosmic rays
Ophiuchus cluster (hard X-ray from Integral, new radio data)
Leptonic Scenarios alone fail to provide self-consistent explanation
Potential complementarity between Fermi and ACTs
Perez-Torres, Zandanel, Guerrero, Pal, Profumo, Prada and Panessa (2009)
2. Clusters: new physics versus cosmic rays
Signal from DM and from CR
in local clusters of galaxies
predicted to be comparable!
Jeltema, Kehaijas and Profumo (2009)
2. Clusters: new physics versus cosmic rays
Most promising targets for
New Physics: nearby
(gas-poor) galaxy groups!
Jeltema, Kehaijas and Profumo (2009)
2. Clusters: ACT and Fermi searches
H.E.S.S. Collaboration, A&A, astro-ph 0907.0727 (~8h observations)
2. Clusters: ACT and Fermi searches
Preliminary
Again, Fermi signal
dominated by IC,
HESS by FSR
More targets, biased
towards those where
the DM/CR ratio is
larger, and brighter
See Tesla Jeltema’s talk; paper in preparation by Fermi Coll.
3. The Milky Way Center and fundamental physics
Rich and complicated Region, with several sources,
large diffuse emission, non-thermal activity
3. The Milky Way Center and fundamental physics
ACT and Fermi observations of Sag A* of fundamental importance
to understand background to the (possibly) brightest DM source
3. The Milky Way Center and fundamental physics
In the limit of perfect control over the diffuse and Sag A* “background”
Fermi can determine fundamental properties of DM from the GC
Jeltema and Profumo (2008)
3. The Milky Way Center and fundamental physics
Self-consistent treatment of both the Sag A* source and DM emission
must however include a multi-wavelength approach
Regis and Ullio (2008)
3. The Milky Way Center and fundamental physics
With certain assumptions on magnetic fields at the GC,
and on the DM annihilation final state
Radio and X-ray data put the gamma-ray emission beyond Fermi sensitivity,
marginally detectable by a CTA
Regis and Ullio (2008)
4. Electrons and Positrons
Great data delivered by H.E.S.S.
on high-energy e+e- flux
Help understanding spectrum
and origin of HE e+e-
Relevance to New Physics:
1. Claim of anomalous
features related to e+ excess
2. Feeds back to diffuse
galactic gamma ray emission
4. Electrons and Positrons
Bottom line of Fermi
e+e- analysis:
* Hard spectrum
* Compatible with
diffuse CR models
* Positron excess
requires extra
primary source
Is there an “anomalous feature” in the Fermi data alone?
Is there a residual
“anomalous spectral feature”
in the Fermi data?
Most probably NO: in the ~ TeV range
• CR Source Spectrum Cutoff
• Diffusion Radius comparable
to mean SNR separation 
source stochasticity effects!
[breakdown of spatial continuity
and steady-state hypotheses]
1- band for large
set of random
SNR realizations
4. Electrons and Positrons: role of ACT’s
•
Maximize overlap with Fermi data at >TeV
•
Check for potential Anisotropy?
•
Cross check HESS results with other ACT
•
Re-calibrate ACT results after Fermi data with GR sources
•
Follow-up on potential local sources of e+e-
Conclusions
New Physics with ACTs in the Fermi Era
•
Complementary Observations
(e.g. dwarfs, clusters, GC, e+e-)
•
ACTs: Potential for Discovery
even in Fermi era
(e.g. clusters as new GR sources, dwarfs)
•
Fundamental to understand
and control Background
(e.g. clusters, GC, e+e-)