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OUTLINE LECTURE 1: SUSY ESSENTIALS LECTURE 2: NEUTRALINOS

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OUTLINE LECTURE 1: SUSY ESSENTIALS LECTURE 2: NEUTRALINOS
OUTLINE
LECTURE 1: SUSY ESSENTIALS
Standard Model; SUSY Motivations; LSP Stability and Candidates
LECTURE 2: NEUTRALINOS
Properties; Production; Direct Detection; Indirect Detection; Collider Signals
LECTURE 3: GRAVITINOS
Properties; Production; Astrophysical Detection; Collider Signals
30 Jul – 1 Aug 07
Feng
1
GRAVITINO COSMOLOGY
• Neutralinos (and all WIMPs) are cold and weaklyinteracting. Is this a universal prediction of SUSY DM?
• No! Here, we’ll consider the gravitino, a SUSY dark matter
candidate with completely different, but equally rich,
implications for particle physics and cosmology
• In some cases, the gravitino has identical motivations to
neutralinos, preserving even the WIMP relic abundance
“coincidence”
30 Jul – 1 Aug 07
Feng
2
Gravitinos
• SUSY: graviton G Æ gravitino G̃
• Mass: in gravity-mediated SUSY breaking, expect
~ 100 GeV – 1 TeV
• G̃ interactions couple
particles to their
superpartners
Couplings grow with
energy, but are typically
extremely weak
30 Jul – 1 Aug 07
G̃
E/MPl
Bµ
B̃
Feng
3
Gravitino Production 1: Thermal
• Gravitinos are the original SUSY DM. First ideas: If the
universe cools from T ~ MPl, gravitinos decouple while
relativistic, expect nG̃ ~ neq.
• Stable:
• Unstable:
(cf. neutrinos). (Current
constraints Æ too hot.)
Decay before BBN Æ
mG̃ > 10-100 TeV
Pagels, Primack (1982)
Weinberg (1982)
Both inconsistent with TeV mass range
30 Jul – 1 Aug 07
Feng
4
Gravitino Production 2: Reheating
• More modern view: gravitino density is diluted by
inflation.
• But gravitinos regenerated in reheating. What happens?
SM interaction rate >> expansion rate >> G̃ interaction rate
• Thermal bath of SM particles and superpartners:
occasionally they produce a gravitino: f f → f G̃
30 Jul – 1 Aug 07
Feng
5
Gravitino Production 2: Reheating
0
• The Boltzmann
equation:
Dilution from
expansion
f G̃ → f f
f f→ f G̃
• Change variables:
• New Boltzmann
equation:
• Simple: Y ~ reheat temperature
30 Jul – 1 Aug 07
Feng
6
Bounds on TRH
•
<σv> for important production
processes:
•
TRH < 108 – 1010 GeV; constrains
inflation
•
G̃ can be DM if bound saturated
30 Jul – 1 Aug 07
Bolz, Brandenburg, Buchmuller (2001)
Feng
7
Gravitino Production 3: Late Decay
• What if gravitinos are diluted by inflation, and the universe
reheats to low temperature?
• G̃ not LSP
• G̃ LSP
SM
LSP
SM
G̃
NLSP
G̃
• No impact – assumption of • A new source of gravitinos
Lectures 1 and 2
Feng, Rajaraman, Takayama (2003)
30 Jul – 1 Aug 07
Feng
8
Gravitino Production 3: Late Decay
• Suppose gravitinos G̃ are the
LSP
≈
• WIMPs freeze out as usual
WIMP
G̃
• But then all WIMPs decay to
gravitinos after
MPl2/MW3 ~ hours to month
Gravitinos naturally inherit the right density from WIMPs, but
interact only gravitationally – they are superWIMPs
30 Jul – 1 Aug 07
Feng
9
SuperWIMP Detection
• SuperWIMPs evade all direct, indirect dark
matter searches
• But cosmology is complementary: Superweak
interactions Æ very late decays to gravitinos Æ
observable consequences
• Signals
– Small scale structure
– Big Bang nucleosynthesis
– CMB µ distortions
30 Jul – 1 Aug 07
Feng
10
SMALL SCALE STRUCTURE
•
SuperWIMPs are produced in late
decays with large velocity (0.1c – c)
•
Suppresses small scale structure,
as determined by λFS, Q
•
Warm DM with cold DM pedigree
•
SUSY does not predict only CDM;
small scale structure constrains
SUSY
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)
30 Jul – 1 Aug 07
Sterile ν
Dodelson, Widronw (1993)
SuperWIMP
Kaplinghat (2005)
Feng
11
BIG BANG NUCLEOSYNTHESIS
Late decays may modify light element abundances
After WMAP
•
ηD = ηCMB
• Independent 7Li measurements
are all low by factor of 3:
Fields, Sarkar, PDG (2002)
30 Jul – 1 Aug 07
Feng
12
BBN EM PREDICTIONS
• Consider τ̃ → G̃ τ
• Grid: Predictions for
mG̃ = 100 GeV – 3 TeV (top to bottom)
∆m = 600 GeV – 100 GeV (left to right)
• Some parameter space
excluded, but much survives
• SuperWIMP DM naturally
explains 7Li !
30 Jul – 1 Aug 07
Feng, Rajaraman, Takayama (2003)
Feng
13
BBN RECENT DEVELOPMENTS
• Much recent progress, results depend sensitively on what
particle decays to gravitino.
• Hadronic decays are important
– constrain χ Æ Ζ G̃ Æ q q G̃
– Slepton, sneutrino decays ok
Kawasaki, Kohri, Moroi (2004); Jedamzik (2004); Feng, Su, Takayama (2004);
Jedamzik, Choi, Roszkowski, Ruiz de Austri (2005)
• Charged particles catalyze BBN: 4He X- + d Æ 6Li + X– Constrain τ̃ → G̃ τ to lifetimes < 104 s, or maybe 106 s ok
– Neutralino, sneutrino decays ok
Pospelov (2006); Kaplinghat, Rajaraman (2006); Kohri, Takayama (2006);
Cyburt, Ellis, Fields, Olive, Spanos (2006); Hamaguchi, Hatsuda, Kamimura, Kino, Yanagida (2007);
Bird, Koopmans, Pospelov (2007); Takayama (2007); Jedamzik (2007)
30 Jul – 1 Aug 07
Feng
14
Cosmic Microwave Background
• Late decays may also distort
the CMB spectrum
• For 105 s < τ < 107 s, get
“µ distortions”:
µ=0: Planckian spectrum
µ≠0: Bose-Einstein spectrum
Hu, Silk (1993)
• Current bound: |µ| < 9 x 10-5
Future (DIMES): |µ| ~ 2 x 10-6
30 Jul – 1 Aug 07
Feng
15
SUPERWIMPS AT COLLIDERS
• Each SUSY event may produce 2 metastable sleptons
Spectacular signature: slow, highly-ionizing charged
tracks
Current bound (LEP): m l̃ > 99 GeV
Tevatron reach: m l̃ ~ 180 GeV for 10 fb-1 (now?)
LHC reach: m l̃ ~ 700 GeV for 100 fb-1
Drees, Tata (1990)
Goity, Kossler, Sher (1993)
Feng, Moroi (1996)
30 Jul – 1 Aug 07
Hoffman, Stuart et al. (1997)
Acosta (2002)
…
Feng
16
Slepton Trapping
• Sleptons can be trapped and
moved to a quiet environment to
study their decays
Slepton
trap
• Crucial question: how many can
be trapped by a reasonably
sized trap in a reasonable time?
Feng, Smith (2004)
Hamaguchi, Kuno, Nakawa, Nojiri (2004)
De Roeck et al. (2005)
30 Jul – 1 Aug 07
Reservoir
Feng
17
Slepton Range
• Ionization energy loss
described by Bethe-Bloch
equation:
water
Pb
m l̃ = 219 GeV
30 Jul – 1 Aug 07
Feng
18
Model Framework
• Results depend heavily on the entire SUSY spectrum
• Consider mSUGRA with m0=A0=0, tanβ = 10, µ>0
M1/2 = 300, 400,…, 900 GeV
30 Jul – 1 Aug 07
Feng
19
Large Hadron Collider
M1/2 = 600 GeV
m l̃ = 219 GeV
L = 100 fb-1/yr
Assume 1 m thick shell of water (10 kton)
Sleptons trapped: ~1%, or 10 to 104 sleptons
30 Jul – 1 Aug 07
Feng
20
International Linear Collider
L = 300 fb-1/yr
Sleptons are slow, most can be caught in 10 kton trap
Factor of ~10 improvement over LHC
30 Jul – 1 Aug 07
Feng
21
IMPLICATIONS FROM DECAYS TO
GRAVITINOS
• Measurement of τ , ml̃ and El Æ mG̃ and GN
–
–
–
–
–
Probes gravity in a particle physics experiment!
Measurement of GN on fundamental particle scale
Precise test of supergravity: gravitino is graviton partner
Determines ΩG̃: SuperWIMP contribution to dark matter
Determines F : supersymmetry breaking scale, contribution of
SUSY breaking to dark energy, cosmological constant
Hamaguchi et al. (2004); Takayama et al. (2004)
30 Jul – 1 Aug 07
Feng
22
ARE WIMPS STABLE?
• Not necessarily. In fact, they can be decaying now:
χ Æ γ G̃
• Signals in the diffuse photon flux, completely
determined by 1 parameter:
Observations and Background
SUSY Signal
Cembranos, Feng, Strigari (2007)
30 Jul – 1 Aug 07
Feng
23
LECTURE 3 SUMMARY
• Gravitinos are excellent SUSY dark matter
candidates
• Many new astrophysical implications for small
scale structure, BBN, CMB, colliders
• If dark matter is at the weak scale, we are
likely to make great progress in identifying it
in the coming years
30 Jul – 1 Aug 07
Feng
24
RECENT BOOKS
30 Jul – 1 Aug 07
Feng
25
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