wimp paradigm: current status 23 mar 11feng 1 fnal colloquium international symposium on experiments...
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WIMP PARADIGM:CURRENT STATUS
23 Mar 11 Feng 1
FNAL Colloquium
International Symposium on Experiments on the Cosmic Frontier
Jonathan Feng
UC Irvine
23 March 2011
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THE WIMP PARADIGM• The WIMP paradigm postulates that particles that help
explain the weak scale are the dark matter. It is the glue that joins together much of the high energy and cosmic frontiers.
• The Rise of the WIMP Paradigm
• Recent Experimental Progress
• Recent Theoretical Progress
23 Mar 11 Feng 2
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THE COSMIC CONNECTION, c. 1977
“Over 500 scientists from around the world are expected to attend a conference at Fermilab Oct. 20-22, 1977. For the first time, physicists working in two frontier areas of science – particle physics and cosmology – will unite to explore the relationship of the universe to inner space of the atom.” – The Village Crier
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THE RISE OF THE WIMP PARADIGM
• We have learned a lot about the Universe in recent years
• There is now overwhelming evidence that normal (atomic) matter is not all the matter in the Universe:
Dark Matter: 23% ± 4%
Dark Energy: 73% ± 4%
Normal Matter: 4% ± 0.4%
Neutrinos: 0.2% (m/0.1eV)
• To date, all evidence is from dark matter’s gravitational effects
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Known DM properties
DARK MATTER
• Not baryonic
Unambiguous evidence for new particles
• Not hot
• Not short-lived
• Gravitationally interacting
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DARK MATTER CANDIDATES
• The observational constraints are no match for the creativity of theorists
• Masses and interaction strengths span many, many orders of magnitude, but masses near the weak scale mweak ~ 100 GeV are especially motivated
HEPAP/AAAC DMSAG Subpanel (2007)
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23 Mar 11
THE WEAK MASS SCALE
• Fermi’s constant GF introduced in 1930s to describe beta decay
n p e
• GF ≈ 1.1 ∙ 10-5 GeV-2 a new mass scale in nature
mweak ~ 100 GeV
• We still don’t understand the origin of this mass scale, but every attempt so far introduces new particles at the weak scale
_
Feng 7
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FREEZE OUT
(1) Assume a new heavy particle X is initially in thermal equilibrium:
XX ↔ qq
(2) Universe cools:
XX qq
(3) Universe expands:
XX qq
23 Mar 11 Feng 8
→←/
→←//
Zeldovich et al. (1960s)
(1)
(2)
(3)
Increasingannihilation
strength
↓
Feng, ARAA (2010)
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0
10 0
102 0
103 0
10-3 0
10-1 0
10-2 0
• The relation between X and annihilation strength is wonderfully simple:
• mX ~ 100 GeV, gX ~ 0.6 X ~ 0.1
23 Mar 11
• Remarkable coincidence: particle physics independently predicts particles with the right density to be dark matter
X
X
q
q_
THE WIMP MIRACLE
Feng 9
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STABILITY
• This all assumes the WIMP is stable
• How natural is this?
New Particle States
Standard ModelParticles
Stable
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LEP’S COSMOLOGICAL LEGACY
• Simple solution: impose a discrete parity, so all interactions require pairs of new particles. This also makes the lightest new particle stable:
LEP constraints ↔ Discrete Symmetry ↔ Stability
• The result: dark matter is easier to explain than no dark matter, and the WIMP paradigm is more natural than ever before, leading to a proliferation of candidates
Cheng, Low (2003); Wudka (2003)
newparticle
Higgs Higgs
Gauge Hierarchy requiresSM
SM SM
SM
new
particle
Precision EW excludes
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EXPERIMENTAL PROBES
Correct relic density Efficient annihilation then
q q
Efficient annihilation now
(Indirect detection)
Efficient scattering now(Direct detection)
Eff
icie
nt p
rodu
ctio
n no
w(P
artic
le c
ollid
ers)
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Dark Matter annihilates in to a place
, which are detected by . some particles an experiment
PAMELA
INDIRECT DETECTIONthe halo
positrons PAMELA/ATIC/Fermi…
ATIC Fermi
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CURRENT STATUS
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PAMELA (2008) ATIC (2008)
e+ + e-
Solid lines are the astrophysical bkgd from GALPROP (Moskalenko, Strong)
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ARE THESE DARK MATTER?
• Energy spectrum shape consistent with WIMP dark matter candidates
• Flux is a factor of 100-1000 too big for a thermal relic; requires
– Enhancement from astrophysics (very unlikely)
– Enhancement from particle physics
– Alternative production mechanismCirelli, Kadastik, Raidal, Strumia (2008)
Arkani-Hamed, Finkbeiner, Slatyer, Weiner (2008)
Feldman, Liu, Nath (2008); Ibe, Murayama, Yanagida (2008)
Guo, Wu (2009); Arvanitaki et al. (2008)
• Pulsars can explain PAMELA
Zhang, Cheng (2001); Hooper, Blasi, Serpico (2008)
Yuksel, Kistler, Stanev (2008); Profumo (2008)
Fermi-LAT Collaboration (2009)
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Fermi-LAT Collaboration (2009)
KK dark matter with m ~ 600 GeV
ATIC (2008)
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ALPHA MAGNETIC SPECTROMETER
• A landmark experiment
• Scheduled for launch in April to the International Space Station
• Can AMS-02 disentangle dark matter from pulsars?
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Pato, Lattanzi, Bertone (2010)
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DIRECT DETECTION• Can look for normal matter
recoiling from DM collisions
• WIMP properties– m ~ 100 GeV– velocity ~ 10-3 c– Recoil energy ~ 1-100 keV
• Typically focus on ultra-sensitive detectors placed deep underground
• But first, what range of interaction strengths are possible to investigate?
DM
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STRONGLY-INTERACTING MASSIVE PARTICLES
Feng 18
• The big picture
Mack, Beacom, Bertone (2007)
• SIMP window is now essentially closed
Albuquerque, de los Heros (2010)
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LOWER LIMIT ON DIRECT DETECTION
• Solar, atmospheric, and diffuse supernova background neutrinos provide an “irreducible background”
• The limits of background-free, non-directional direct detection searches (and also the metric prefix system!) will be reached by ~10 ton experiments probing
~ 1 yb (10-12 pb,10-48 cm2)
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Strigari (2009); Gutlein et al. (2010)
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LOW CROSS SECTION FRONTIER• Focus here on spin-independent
results, which are typically normalized to X-proton cross sections
• Weak interaction frontier: For masses ~ 100 GeV, many models 10-44 cm2 (see LHC below)
CDMS in the Soudan mine (Minnesota)
Aprile et al. (2010)(updated)
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Collision rate should change as Earth’s velocity adds constructively/destructively with the Sun’s annual modulation
Drukier, Freese, Spergel (1986)
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DA
MA
(2008)
DAMA: 8 signal with T ~ 1 year, max ~ June 2
LOW MASS FRONTIER
DAMA low mass signal now supplemented by CoGeNT
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• Puzzles– Low mass and high – DAMA ≠ CoGeNT – Excluded by XENON, CDMS
• Many proposed explanationsHooper, Collar, Hall, McKinsey (2010); Fitzgerald, Zurek
(2010); Fox, Liu, Weiner (2010)
ARE THESE DATA CONSISTENT?• Isospin-Violating Dark Matter
– Scattering is coherent:
A ~ [ fpZ + fn (A-Z) ]2 – Typical plot assumes fn = fp
– Can reconcile DAMA, CoGeNT, XENON with fn = -0.7 fp
Giuliani (2005); Chang, Liu, Pierce, Weiner, Yavin (2010)
Feng, Kumar, Marfatia, Sanford (2011)
Need more than one target material and more than one experiment per material
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SPIN-DEPENDENT SCATTERING
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PARTICLE COLLIDERS
LHC: ECOM = 7-14 TeV, [Tevatron: ECOM = 2 TeV,]
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CURRENT BOUNDS FOR SUSY
Feng, Matchev, Wilczek (2003)
Yellow: pre-WMAPGreen: post-WMAP
p ~
10
-44 c
m2
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Neutralinos need an efficient annihilation channel
HOW MODEL-INDEPENDENT IS THIS?
Co-annihilation
region
Degenerate and stau
Bulk
regionLight
sfermions
Focus point
region
Mixed Higgsino-BinoNeutralinos
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Aprile et al. (2010)(updated)
23 Mar 11
THE SIGNIFICANCE OF 10-44 CM2
• The LHC is eliminating one process. If M2 > M1, no co-annihilation, resonances, this fixes the neutralino’s coupling to Ws
• But this also fixes the DM scattering through Higgs
• Predictions collapse to a band Feng 27
q
h
q
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few 10-44 cm2
No signal
Signal
few 10-45 cm2
STATUS OF NEUTRALINO DM
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BEYOND WIMPS
• Does the WIMP paradigm imply WIMPs?
• The WIMP miracle seemingly implies that dark matter is– Weakly-interacting– Cold– Collisionless
Are all WIMP miracle-motivated candidates like this?
• No! Recently, have seen many new classes of candidates. Some preserve the motivations of the WIMP paradigm, but have qualitatively different properties
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SUPERWIMPSFeng, Rajaraman, Takayama (2003); Bi, Li, Zhang (2003); Ellis, Olive, Santoso, Spanos (2003);
Wang, Yang (2004); Feng, Su, Takayama (2004); Buchmuller, Hamaguchi, Ratz, Yanagida (2004); …
• Suppose the WIMP can decay into a superweakly-interacting particle (superWIMP):
• This is not completely contrived: it happens about ½ the time in simple SUSY, where the gravitino plays the role of the superWIMP:
WIMP (mass + charge) superWIMP (mass) + SM particles (charge)
SuperWIMP
WIMP
SM particles
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FREEZE OUT WITH SUPERWIMPS
SuperWIMPs naturally inherit the right density; share all the motivations of WIMPs, but are much more weakly interacting
…but then decay to superWIMPs
WIMPs freeze out as usual…
MPl2/MW
3 ~ 103-106 s
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CHARGED PARTICLE TRAPPING• SuperWIMPs are produced by
decays of metastable particles, which can be charged
• Charged metastable particles will be obvious at colliders, can be trapped and moved to a quiet environment to study their decays
• Can catch 1000 per year in a 1m thick water tank
Feng, Smith (2004)
Hamaguchi, Kuno, Nakawa, Nojiri (2004)
De Roeck et al. (2005)
Chargedparticle
trap
Reservoir
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• SuperWIMPs are produced at “late” times with large velocity (0.1c – c)
• Suppresses small scale structure, as determined by FS, Q
• Warm DM with cold DM pedigree
WARM SUPERWIMPS
Dalcanton, Hogan (2000)Lin, Huang, Zhang, Brandenberger (2001)
Sigurdson, Kamionkowski (2003)Profumo, Sigurdson, Ullio, Kamionkowski (2004)
Kaplinghat (2005)Cembranos, Feng, Rajaraman, Takayama
(2005)Strigari, Kaplinghat, Bullock (2006)Bringmann, Borzumati, Ullio (2006)
Kap
linghat (2005)
Sterile Dodelson, Widrow (1993)
SuperWIMP
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HIDDEN DARK MATTER
• Hidden sectors are composed of particles without SM interactions (EM, weak, strong)
• Dark matter may be in such a sector– Interesting self-interactions, astrophysics– Less obvious connections to particle physics– No WIMP miracle Spergel, Steinhardt (1999); Foot (2001)
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SMHidden
X
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• In SUSY, however, there may be additional structure. E.g., in GMSB, AMSB, the masses satisfy mX ~ gX
2
• This leaves the relic density invariant
• “WIMPless Miracle”: hidden sectors of these theories automatically have DM with the right (but they aren’t WIMPs)
• Is this what the new physics flavor problem is telling us?!
23 Mar 11
THE WIMPLESS MIRACLE
Feng 35
Feng, Kumar (2008); Feng, Tu, Yu (2009)
WIMPs
WIMPless DM
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WIMPLESS DM SIGNALS
• Hidden DM may have only gravitational effects, but still interesting: e.g., it may interact through “dark photons”, self-interact through Rutherford scattering
Ackerman, Buckley, Carroll, Kamionkowski (2008)
Feng, Kaplinghat, Tu, Yu (2009)
• Alternatively, hidden DM may interact with normal matter through connector particles, can explain DAMA and CoGeNT signals
X
X
f
fY
Kum
ar, Learned, Sm
ith (2009)
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CONCLUSIONS
• Particle Dark Matter– Central topic at the interface of cosmology and particles– Both cosmology and particle physics weak scale ~ 100 GeV
• WIMP Paradigm– WIMPs: Many well-motivated candidates– SuperWIMPs, WIMPless dark matter: Similar motivations, but
qualitatively new possibilities (warm, collisional, only gravitationally interacting)
– Many others
• LHC is running, direct and indirect detection, astrophysical probes are improving rapidly – this field will be transformed soon