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WIMPs and superWIMPs
Jonathan Feng
UC Irvine
MIT Particle Theory Seminar
17 March 2003
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17 March 2003 MIT Feng 2
Dark Matter• The dawn (mid-morning?) of precision cosmology:
DM = 0.23 0.04
total = 1.02 0.02
baryon = 0.044 0.004
t0 = 13.7 0.2 GyrWMAP (2003)
• We live in interesting times:We know how much dark matter there is We have no idea what it is
• Our best evidence for new particle physics
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WIMPs• Weakly-interacting particles with
weak-scale masses decouple with DM ~ 0.1; this is remarkable
[Cf. quarks with natural B ~10-11 ]
• Either– a devious coincidence,
or – a strong, fundamental, and
completely cosmological motivation for new physics at the electroweak scale
Jungman, Kamionkowski, Griest (1995)
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Outline
• Explore new possibilities for particle dark matter
• Guiding principles:
– Must be well-motivated from particle physics viewpoint
– Must naturally produce desired DM (this is all we know!)
WIM
Ps
supe
rWIM
Ps
SUSY Extra D
FRT*
CFM*
*Cheng, Feng, Matchev (2002)*Feng, Rajaraman, Takayama (2003)
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SUSY WIMPs
Feng, Matchev, Wilczek (2000)
Relic density regions and gaugino-ness (%)
• Neutralinos:• fermionic partners of
, Z, W0, h0
• DM ~ 0.1 in much of parameter space
• Requirements:• high supersymmetry
breaking scale (supergravity)
• R-parity conservation
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SUSY WIMP Detection
Particle probesDirect DM detectionIndirect DM detection
• Astrophysical and particle searches are promising: many possible DM signals before 2007
• This is generally true of WIMPs: undetectable weak interactions weak annihilation too much relic density
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Extra D WIMPs
• Kaluza (1921) and Klein (1926) considered D=5, with 5th dimension compactified on circle S1 of radius R:
D=5 gravity D=4 gravity + EM + scalar
GMN G + G5 + G55
• Kaluza: “virtually unsurpassed formal unity...which could not amount to the mere alluring play of a capricious accident.”
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• Problem: gravity is weak
• Solution: introduce extra 5D fields: GMN , VM , etc.
• New problem: many extra 4D fields; some with mass n/R, but some are massless! E.g., 5D gauge field:
• New solution…
good
bad
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• Compactify on S1/Z2 instead (orbifold); require
• Unwanted scalar is projected out:
• Similar projection on fermions chiral 4D theory, …
• Very simple (requires UV completion at R)Appelquist, Cheng, Dobrescu (2001)
good
bad
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KK-Parity• An immediate consequence: conserved KK-parity KK
Interactions require an even number of odd KK modes
• 1st KK modes must be pair-produced at colliders
• weak bounds: R > 200 GeV
• LKP (lightest KK particle) is stable – dark matter!
Appelquist, Yee (2002)
Macesanu, McMullen, Nandi (2002)
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Other Extra D Models
• SM on brane; gravity in bulk (brane world)– Requires localization mechanism– No concrete dark matter candidate
• fermions on brane; bosons and gravity in bulk– Requires localization mechanism– R > few TeV from f f V
1 f f– No concrete dark matter candidate
• everything in bulk (Universal Extra D)– No localization mechanism required– Natural dark matter candidate – LKP
_ _
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UED and SUSYSimilarities:• Superpartners KK partners• R-parity KK-parity• LSP LKP• Bino dark matter B1 dark matter
Sneutrino dark matter 1 dark matter...
Not surprising: SUSY is also an extra (fermionic) dimension theory
Differences:• KK modes highly degenerate, split by EWSB and
loops• Fermions Bosons
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Minimal UED KK Spectrum
Cheng, Matchev, Schmaltz (2002)
loop-levelR = 500 GeV
tree-levelR = 500 GeV
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Extra D WIMPs
• LKP is nearly pure B1 in minimal model (more generally, a B1-W1 mixture)
• Relic density:Annihilation through
Preferred mass range ~ 1 TeV, variations from co-annihilations Servant, Tait (2002)
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Co-annihilation
• But degeneracy co-annihilations important
• Co-annihilation processes:
• Preferred mB1: l1 lowers it, q1 raises it; 100s of GeV to few TeV possible
Dot: 3 generationsDash: 1 generation1% degeneracy5% degeneracy
Servant, Tait (2002)
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• s-channel enhanced by
B1-q1 degeneracy
• Constructive interference: lower bounds on scalar , spin
B1 Dark Matter Detection
Direct Detection
Cheng, Feng, Matchev (2002)
t-channelh exchange
s- and u-channelB1q q1 B1q
scalar spin
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B1 Dark Matter Detection
• Indirect Detection: – Positrons from the galactic halo– Muons from neutrinos from the Sun and Earth– Gamma rays from the galactic center
• All rely on annihilation, very different from SUSY– For neutralinos (Majorana fermions), f f is
chirality suppressed– B1B1 f f isn’t; generically true for bosons
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Positrons
Cheng, Feng, Matchev (2002)
• Here fi(E0) ~ (E0mB1), and thepeak is not erased by propagation(cf. W+Wee)
• AMS will have e/e separation at 1 TeV and see ~1000 e above 500 GeV
Moskalenko, Strong (1999)
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Muons from Neutrinos
Cheng, Feng, Matchev (2002)Hooper, Kribs (2002)
Bertone, Servant, Sigl (2002)
• Muon flux is
• B1B1 is also unsuppressed, gives hard neutrinos, enhanced flux
Ritz, Seckel (1988)Jungman, Kamionkowski, Griest (1995)
Discovery reach
dege
nera
cy
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Gamma Rays
Cheng, Feng, Matchev (2002)
• B1B1 is loop-suppressed, but light quark fragmentation gives hardest photons, so absence of chirality suppression helps again
• Results sensitive to halo clumpiness; choose moderate value
Bergstrom, Ullio, Buckley (1998)
Integrated photon flux ( J = 500)_
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What about KK gravitons?
• G1 may be the LKP. In fact, loop contributions, typically positive, are negligible for G1.
• For that matter, what about gravitinos in SUSY? In supergravity,
m3/2 ~ m0 ~ M1/2 ~ <F>/MPl,
unknown O(1) coefficients determine ordering. The gravitino may be the LSP.
• These possibilities are very similar; consider in parallel.
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superWIMPs
• Suppose LKP is G1. If NLKP is B1, B1 freezes out with the usual desired , then decays much later via B1 G1
• G1 inherits the desired retains all WIMP virtues
• BUT: G1 is superweakly-interacting, and so undetectable by all dark matter searches
• Only possible signal is in WIMP superWIMP decays
Feng, Rajaraman, Takayama (2003)
gravitino graviton
msWIMP = 0.1, 0.3, 1 TeV (from below)
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BBNExcluded Regions (shaded)
• Late decays may destroy BBN light element abundance predictions
• typically quickly thermalize, BBN constrains total energy release X = nSWIMP / nBG
• Constraints weak for early decays: universe is hot,
BG e+e suppresses spectrum at energies above nuclear thresholds
Cyburt, Ellis, Fields, Olive (2002)
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CMB
gravitino graviton
mSWIMP as indicated
Excluded regions (above CMB contours)
• Late decays may also destroy black-body spectrum of CMB
• Again get weak constraints for early decays, when e e
e X eX e e
are all effective
• superWIMP DM:
• mWIMP, mSWIMP ,
• SWIMP = DM abundance YSWIMP
Feng, Rajaraman, Takayama (2003)
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superWIMP Dark Matter
gravitino graviton
Weak-scale superWIMPs are viable cold dark matter
Feng, R
ajaraman, T
akayama (2003)
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Is it testable?
• BBN versus CMB baryometry is a powerful probe
Cyburt, Fields, Olive (2003)Fields, Sarkar, PDG (2002)
WMAP
D = CMB
but
7Li is low
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7Li low
4He low
D low
D high
105 s
3 105 s
106 s
3 106 s
107 s
X and
10-8 GeV
3 10-9 GeV
10-9 GeV
3 10-10 GeV
10-10 GeV
Feng, Rajaraman, Takayama (2003)Cyburt, Ellis, Fields, Olive (2002)
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Conclusions
• Guiding principles:– well-motivated particle physics– naturally correct DM
• WIMPs from Extra Dimensions– B1: qualitatively new signals– Many other candidates to investigate
• superWIMPs: gravitinos/gravitons naturally yield desired thermal relic density, but are inaccessible to all conventional searches– Bino NLSP: BBN, CMB signals– Many other NLSP candidates to investigate
• Escape from the tyranny of neutralino dark matter!W
IMP
ssu
perW
IMP
s
SUSY Extra D