stefano profumo university of california, santa cruz santa cruz institute for particle physics tev...
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Stefano ProfumoUniversity of California, Santa Cruz
Santa Cruz Institute for Particle Physics
TeV Particle Astrophysics 2013University of California, Irvine, August 29, 2013
Astrophysical Probes of Dark Matter
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3 tantalizing results might start delivering fundamental physics from the sky
A 130 GeV lineGamma-ray excess in the Galactic Center?
Cosmic-Ray Positron Excess
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Cosmic-Ray Positron Excess
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Adriani et al, Nature 458 (2009) 607, arXiv 0810.4995*I.V. Moskalenko and A.W. Strong Astrophys. J. 493, 694-707 (1998).
Theory Prediction*
>>1000 CITATIONS!
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Gast & Schael, ICRC Conference, Lodz, 2009
22 years full cycle (max every 11 years, with polarity reversal)previous data: solar polarity favored positively charged
particles, opposite for PAMELA
Low-Energy: correct for(charge-dependent)
solar modulation
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image credit: Philip Mertsch
Cosmic Ray Secondary-to-Primary ratio
sources of Cosmic Ray protons and electrons, e.g. SNR
Diffusion “softens” the proton spectrum;secondaries inherit a softer spectrum
~ any cosmic ray model predicts a declining slope for high-energy
secondary-to-primary ratios
High-energy protons diffuse before producing secondaries
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is the positron excess real?
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Superluminal Neutrinos @ OPERA:>200 theory papers
Experimentalists get ignored if they are right, and hugely cited if they are wrong.
Theorists get ignored if they are wrong, but a Nobel Prize if they are right.*
* quoted from the Guardian
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How does Fermi tells e+ apart from e-?
Fermi-LAT Collaboration, 1109.0521
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Geomagnetic field + solid Earth shadow = directions from which only electrons or only
positrons are allowed
Slide concept: Justin Vandenbroucke
e- blocked while e+ allowed from West
e+ blocked while e-
allowed from East
For particular directions, electrons or positrons are completely forbiddenPure e+ region looking West and pure e- region looking EastRegions vary with particle energy and spacecraft position
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AMS-02 first results confirm positron excess with very high statistics (x100)
April 3, 2013
PRL, 110 (2013) 14
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…better take seriouslythe excess of HE positrons
Can we determine the source/origin?
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Note: this is all consistent with Eli’s upper limit on secondaries
A marketing problem: if data are consistent with a general,
model-independent upper limit, we don’t necessarily understand/predict the physical origin of the HE positrons!
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Galactic Cosmic Ray acceleration should
produce a power-law e+e- injection spectrum
with a high-energy cutoff
Fermi-LAT Collaboration, Phys Rev D 82 (2010) 092004, arXiv:1008.3999
Fermi/HESS data compatible with an additionalhigh-energy source
key piece of the puzzle: the Denominator (e+ + e-)
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Solution: postulate additional source of (high-energy) electrons and positrons:
What is the nature of this new powerful electron-positron source??
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Image Credit: NASA/GLAST collaboration
Exciting! It could be New Physics:
Dark Matter Annihilation!
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A. Tylka, Phys. Rev. Lett. 63, 840-843 (1989)
Dark Matter particle mass
Exciting! It could be New Physics:
Dark Matter Annihilation!
M. Turner and F. Wilczek, Phys Rev. D 42 (1990) 1001.
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Exciting! It could be New Physics:
Dark Matter Annihilation!
…or it could not…
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Harding, A. K. & Ramaty, R. The pulsar contribution to galactic cosmic-ray positrons.
Proc. 20th ICRC, Moscow 2, 92-95 (1987).
Pulsar MagnetosphereRotation-powered Neutron Stars radiate
energy by producing e+e- pairs, injected in ISM when out of
Pulsar Wind Nebula
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>1000 papers advocate Dark Matter…despite some obvious and significant issues:
(i) Need very large annihilation rates (<sv> ~ 102-103 x 10-26 cm3/s)
(ii) Need rather large masses (~TeV)
(iii) Need special annihilation or decay modes(suppress antiprotons + have a hard spectrum)e.g.: m+m-, or 4 m (even worse post-AMS: pp)
…an interesting riddle to test a theorist’s creativity!
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Redman’s Theorem
Roderick O. Redman
(b. 1905, d. 1975)
Professor of Astronomy
at Cambridge University
“Any competent theoreticiancan fit any given theory
to any given set of facts” (*)
(*) Quoted in M. Longair’s “High Energy Astrophysics”, sec 2.5.1 “The psychology of astronomers and astrophysicists”
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“Dissecting Pamela with Occam's Razor: existing, well-known Pulsars naturally account for the "anomalous" Cosmic-Ray Electron and Positron Data”*
*Profumo, 0812.4457
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Linden and Profumo, 1304.1791
• Distance and Age from observation (set the cutoff)• Normalization: 1-10% spin-down luminosity• Injection Spectrum: ~ E-2 (Fermi 1st order)
…PulsarsPost AMS
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can we discriminate between
dark matter and pulsars?
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Nearby PulsarAnisotropy in the arrival direction
(sufficient, not necessary)
Dark MatterDiffuse
secondary component
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Dark MatterDiffuse
secondary component
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Dark Matter: a “Universal” Phenomenology
Large annihilation ratesLarge masses
Hard charged leptons
Final State Radiation Inverse Compton
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Jeltema, Profumo & Fermi-LAT Collaboration, JCAP 2010, arXiv: 1001.4531
Gamma-Ray Searches from Galaxy Clusters
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no substructure
galaxies only
Jeltema, Profumo & Fermi-LAT Collaboration, JCAP 2010, arXiv: 1001.4531
Gamma-Ray Searches from Galaxy Clusters
…ruled out!
Fermi
AMS
AMS(best fit)
No
cuto
ff
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no substructure
galaxies only
Jeltema, Profumo & Fermi-LAT Collaboration, JCAP 2010, arXiv: 1001.4531
substructure with M > 10-6 MSun
Additional constraints from CMB,extragalactic gamma-ray background
Gamma-Ray Searches from Galaxy Clusters
AMS(best fit)
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Nearby PulsarAnisotropy in the arrival direction
(sufficient, not necessary)
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No Anisotropy observedin the Fermi e+e- data,
or in the AMS data
Fermi-LAT Collaboration, PRD, 1008.5119AMS-02 Collaboration, PRL, 110, 141102
Pulsars
Excludedby Fermi data
Monogem
Vela
Vela
Monogem
Pulsar interpretationentirely consistent
with all data!!
Excludedby AMS data
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Linden and Profumo, Astroph. J (2013) 1304.1791
Way forward: Cherenkov Telescopes sensitive to predicted anisotropies at VHE!
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we are closing in on the dark matter interpretation
AMS-02 positron fraction data “favor” PSR’s over dark matter
Conclusive argument against dark matter: anisotropy (ACTs!)
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Dark Matter annihilation in the Galactic Center?
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the problem with the Galactic Center:“under-fitting” versus “over-fitting”
Dark Matter annihilation in the Galactic Center?
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The Galactic Center Region: a Holy Grail or a Hornet’s Nest?
• Largest (known) Galactic Dark Matter Density• There appears to be an excess of soft gamma rays
Springel et al, 2009
• Largest Cosmic Ray Density• Largest Gas and Radiation Densities• Largest concentration of Galactic Gamma Ray sources
Kassim et al, 1999
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Oct. 2009Goodenough, Hooper
Exponential angular fall-offPower-law spectrum 28 GeV, bb quark
Background Dark Matter particle
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Oct. 2009Goodenough, Hooper
Background Dark Matter particle
Oct. 2010Hooper, Goodenough
r -1.55 fall-offSpectrum: extracted
from >2deg region 8 GeV, t + t -
Exponential angular fall-offPower-law spectrum 28 GeV, bb quark
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the danger of background “under-fitting”:
may end up with a “Goodenough Hooperon”
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Exponential angular fall-offPower-law spectrum 28 GeV, bb quarkOct. 2009
Goodenough, Hooper
Background Dark Matter particle
Oct. 2010Hooper, Goodenough
r-1.55 fall-offSpectrum: extracted from >2deg region 8 GeV, t + t -
Oct. 2011Linden, Hooper
Angular distrib: gas mapsSpectrum from: p0 decay
plus point-source
~10 GeV, t + t – or bb,
or genericdiffuse excess
Several recent studies confirmed the 2011 Linden-Hooper excess
(Abazijian and Kaplinghat, 2012; Hooper and Slatyer 2013)
Very intriguing mass range(see CDMS+CoGeNT ~ 10 GeV mass WIMPs)
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e+-
PHe
CNO
X,γ
gas
gas
ISRF
e+-
π+-
P_
LiBeB
ISM
diffusion energy losses
reacceleration convection
etc.
π0
synchrotron
IC
bremss
Chandra
Fermi-LAT
ACEhelio-modulation
p
HESS Preliminary
SNR RX J1713-3946
PSF
B
HeCNO
Flu
x
20 GeV/n
CR species: Only 1 location modulation
e+-
π+-
PAMELABESS
AMS
[slide from Igor Moskalenko]
“Over-fitting”
Fine-tune the model
Gobble up any signal!
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e+-
PHe
CNO
X,γ
gas
gas
ISRF
e+-
π+-
P_
LiBeB
ISM
diffusion energy losses
reacceleration convection
etc.
π0
synchrotron
IC
bremss
Chandra
Fermi-LAT
ACEhelio-modulation
p
HESS Preliminary
SNR RX J1713-3946
PSF
B
HeCNO
Flu
x
20 GeV/n
CR species: Only 1 location modulation
e+-
π+-
PAMELABESS
AMS
[slide from Igor Moskalenko]
“Over-fitting”
some diffuse models designed to deal optimally with point sources:
“over-fitting” is welcome in that case!
beware of how any “no-residuals”conclusion is obtained!
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One of the elephants in the room: Sgr A*
We know little about cosmic rays in the GC
CR power: ~1041 erg/s; Sag A* Eddington lum.: >1044 erg/s
While very quiet now, Sag A* likely accelerates and has accelerated protons: study the gamma-ray properties
Linden, Lovegrove and SP, 1203.3539 and in prep.
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One of the elephants in the room: Sgr A*
K. Ferrere, 2012; Linden and Profumo, 2012
Need detailed modeling of gas distributionOur approach: Monte Carlo
If source is hadronic,GALPROP likely is the wrong tool
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Linden, Lovegrove and SP, 1203.3539, ApJ 753 (2012) 41
One of the elephants in the room: Sgr A*
transition between diffusively trapped behavior and rectilinear propagation
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Key diagnostic: source morphologysecondary (leptonic) emission
Chernyakova et al, 2011; Linden, Lovegrove and SP, 1203.3539, ApJ 753 (2012) 41
One of the elephants in the room: Sgr A*
transition between diffusively trapped behavior and rectilinear propagation key diagnostics:
circum-nuclear ring!
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Linden, SP,…, in progress
• seek a “golden mean” between over- and under-fitting
• detailed cosmic ray and target density models
• data-driven backgrounds
Galactic Center: the way forward??
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The Gamma-Ray Line
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“Troubling and Inconclusive”
Steve RitzFermi-LAT Deputy PI
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If confirmed, huge impact on particle physics!
DM particle at rest, so cc gg implies Eg=mc!
mc sets the missing energyscale for collider studies
…and the target mass for direct detection experiments!
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Weniger (1204.2797)
Key novelty: optimized Regions of Interest
Signal: ~(rDM)2
Noise: (1-20 GeV sky)1/2
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(almost) 3s effect, Eg=130 GeVlook-elsewhere effect accounted for
1s2s3s
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Two remarks*
* Profumo and Linden, “Gamma-Ray Line in the Fermi Data: is it a Bubble?”, JCAP 2012
(1) ROI’s overlap with Fermi bubbles: photons from bubbles are important background
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(1) ROI’s overlap with Fermi bubbles: photons from bubbles are important background
(2) broken power-law could be mistaken for a line - Fermi bubbles have broken power-law spectrum
Two remarks*
* Profumo and Linden, “Gamma-Ray Line in the Fermi Data: is it a Bubble?”, JCAP 2012
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One culprit could be energy reconstruction: E>130 GeV mis-read as E=130 GeV event!
Instr. effects under investigation by Fermi Collaboration,including troubling Earth’s Limb feature!
[Pass 8: currently being tested internally/public in ~1yr]
If not instrumental, potentially very interestingwait for more statistics (so far ~50 photons)!
could it be aninstrumental effect?
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can we hope for more statistics with other existing/near future telescopes?
e.g., HESS: promising, but Aeff rapidly declining in energy region of interest
Fermi: AeffxTobs = (1 m2) x 4px107 x (1/6) s ~ 2x107 m2 s
ACT, with 100h: (105 m2) x 100x60x60 s ~ 3x1010 m2 s
Figure credit: Benow, for HESS collaboration
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CTA: superior energy resolution, angular resolution, energy threshold
and effective area13
0 G
eV
Cherenkov Telescopes will be keyfor further studies of the line
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Need~ mono-chromatic electrons and target photons with w0 >> me
2/Ee ~ 2 eV
Both OK with electron pulsar wind
Klein-Nishina regime: almost all energy transferred from e to g Ee~ 130 GeV
Aharonian et al, 2012; image credit: NASA
Astrophysical backgrounds? Always keep Occam in mind!
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This is not a POST-diction!
Bogovalov and Aharonian, 2000
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Aharonian et al, Nature 2012
Energetics works out fine!130 GeV line luminosity ~ 3x1035 erg/s
Crab luminosity in shock-acc. e+e- ~ 3x1038 erg/s[spin-down luminosity~ 5x1038 erg/s ]efficiency to produce gamma rays??
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Many open questions…
• how many point sources are needed?
• if more than one astrophysical source is needed, do we expect 130 GeV to be a special universal value?
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Carlson, Linden, Profumo and Weniger, JCAP, 1304.5524 (2013)
Applied a clustering algorithm (DBSCAN) and demonstrated one needs at least 5 pulsars (@90%CL)
Astrophysical backgrounds are unlikely, given current data!
actual data 3 pulsarssimulation
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130 GeV line “troubling and inconclusive”, yet exciting!
low statistics, perhaps instrumental, but unlikely “astrophysical”
look forward to: Fermi’s Pass8 and ACT
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mass ~ 1 TeV, m+m- (more likely pp)
mass ~ 10 GeV, bb or t+t-
mass = 130 GeV, enhance line, no continuum
A (dark matter) model that does everything?
130 GeV line
Galactic Center
Positron Excess
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“Ambulance chasing OK, as long as the patient is not dead”
Is this all “chasing ambulances”?
Positron excess, Galactic Center excess, “The Line”