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Exploring Dark Matter From Colliders To The Cosmos
Hai-Bo YuUniversity of Michigan, Ann Arbor
HET Seminar, TAMU10/29/2012
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Outline• A brief introduction
• WIMP dark matter An effective field theory approach
Searches at colliders
• Beyond the WIMP paradigm Asymmetric dark matter
Hidden sector dark matter
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We Need Dark Matter
• Not luminous• Not short-lived• Not hot• Dissipation-less X ‣Mass
‣Spin‣Quantum Number
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The WIMP “Miracle”X
X
SM (q,l...)
SM (q,l...)_ _
ΩX ∼ 0.23
3× 10−26 cm3/s
σAv
Weak-scale cross section
A remarkable coincidence!
Dark matter indicates weak-scale new physics!
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Hunt For WIMPsLHC
NeutronStars
X SM
SMX
Indirect detection (now)Relic density (early Universe)
Dir
ect
dete
ctio
n
Collider Search
AMS PAMELA
IceCube
LHC
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Direct Detection Status
• Three experiments saw something • The preferred regions do not overlap (simple WIMP models) • They conflict with results from CDMS and XENON
We need a better understanding
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Challenges
Colliders can provide complementary searches
No A dependence
∼ SX · SN
Spin-dependent WIMP
Nucleus
Coherent scattering Cross section ~A2 Enhanced by a large A
Spin-independent
Low m
ass
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Collider Search
X SM
SMX
Indirect detection
Dir
ect
dete
ctio
nCollider Search
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WIMPs at Colliders
X
X
q
q_
Time
q_
q X
XTime
gluon(jet)/photon/Zq X
X
⟿q_
Time
⟿X
X
p p_
Visible
Invisible pp→Monojet+Missing Energy _
Goodman, Ibe, Rajaraman, Shepherd, Tait, HBY (2010) PRD, PLB, NPB
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WIMPs at Colliders
How sensitive to the details?
q X
X
⟿
q_
?
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Effective Theory Approachq X
Xq_
Q∼ gqgX
Q2 −m2φ
q X
Xq_
∼ gqgXm2
φ
=1
M2∗
If mφ Q
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The Power of Effective Theoryq
X
q
X
σDD ∼ µ2
M4∗
µ ∼ 1 GeV σj ∼ αsp2TM4
∗pT ∼ 100 GeV
σj
σDD∼ αs
p2Tµ2
∼ O(1000)
Direct detection and collider production are correlated directly• If there is an excess, σDD~σj/1000• Otherwise σj<σmax, σDD<σmax/1000
q
q
X
X
⟿gluon (jet)
M* M*
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Back of the Envelope
Events: monojet+missing energy
Predicted from the SM: 8663±332
Observed at the Tevatron: 8449
Allowed contributions from WIMPs: 332⨉2=664
σj⨉1 fb-1⩽664 ⇒ σj⩽664 fb
σDD~σj/1000 ⩽ 0.664 fb~6.6⨉10-40 cm2
Tevatron CDF luminosity 1 fb-1
http://www-cdf.fnal.gov/physics/exotic/r2a/20070322.monojet/public/ykk.html
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Back of the Envelope
Colliders can provide complementary searches for light WIMPs and WIMPs with SD scattering
below 5-10 GeV
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An Effective Theory of Dark Matter
Goodman, Ibe, Rajaraman, Shepherd, Tait, HBY (2010)
X
X
q
q
Invariant under Lorentz symmetry and U(1)em
The cut-off scale controls everything
M*
see also: Bai, Fox, Harnik (2010)
CDF, ATLAS and CMS have done the analysis
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Recent ATLAS Results
D1 : χχqq D5 : χγµχqγµq D11 : χχGµνGµν
D8 : χγµγ5χqγµγ5q D9 : χσµνχqσµνq
arXiv:1210.4491
The LHC provides complementary searches
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Beyond the Effective Theory
Fox, Harnik, Kopp, Tsi (2011)
• If the mediator is light, the EFT approach breaks down• The monojet+MET search is still valid • The bound depends on details of the WIMP theory
σj ∼ αsp2TM4
∗
σj ∼ αs1
p2T
heavy mediator
light mediator
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Limits from the Fermi-LAT
Goodman, Ibe, Rajaraman, Shepherd, Tait, HBY (2010)
Spin-dependent WIMP-nucleon scattering
M∗
X
X
qɣ/Z
ɣ
Fermi-LAT (2010)
D8 : χγµγ5χqγµγ5q
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The 130 GeV Line signal?
Weniger (2012) see also Su, Finkbeiner (2012)
mχ 130 GeV
σvγγ ∼ 10−27 cm3/s
See for example: Sean, HBY, Zurek (2012)
Not the usual WIMP
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Beyond the WIMP Paradigm• WIMPs satisfy all cosmological requirements to be dark
matter candidates
• Moreover, the WIMP paradigm is very predictive
• The effective field theory is a powerful tool
• Colliers provide complementary searches for WIMPs
• Beyond the WIMP paradigm: asymmetric dark matter and hidden sector dark matter
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Asymmetric Dark Matter• Baryon asymmetry in the universe
Nussinov (1985); Kaplan (1992); Kaplan, Luty, Zurek (2009); Dutta, Kumar (2010); Tulin, HBY, Zurek (2012)...
ηB =nB − nB
s∼ 10−10 ηX =
nX − nX
s= 0
ΩX =ηXsmX
ρc
ηX ∼ ηB ,mX ∼ mBΩX/ΩB ∼ 5 GeV
XX
_X
XX
_X
X_
• The usual WIMP is in the symmetric limit
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Stars as Natural Labs
• Stars capture dark matter particles gravitationally
• They scatter with baryons and lose energy
• They are trapped in stars
Gould (1987)
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An Interesting Application
Mack, Beacom, Bertone (2007)
• Earth captures WIMPs• WIMP annihilation produces heat • Inside the heavily-shaded region, WIMP annihilation would overheat Earth
Underground
detecto
rs
Capture rate ∝σ
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ADM VS. Symmetric WIMP
A speculated event: Captured ADM particles collapse to a mini black hole at the center of neutron stars
Capture rate∝σ
• Symmetric DM: NX~constant
• Asymmetric DM: NX∝t
Example: Scalar asymmetric dark matter
• Neutron stars as natural labs for ADM
Neutron star
ADM
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ADM in Neutron Stars
Thermal states
⟿⟿⟿⟿BEC
Neutron star
ADM
Thermal
BEC
Thermal
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ADM in Neutron Stars
Step 1: Capture
Step 2: Dark Matter Cooling
after 30 minutes
An example: ADM mass 10 GeV
Step 3: Bose-Einstein Condensation
ADM number in the BEC state
σn = 2× 10−45 cm2
N totalX ∼ 1042
tth ∼ 30 minutes
vhalo ∼ 10−3c vesc ∼ 0.6c
vth ∼ 3× 10−5c
N critX ∼ 1036
NBECX = N total
X −N critX ∼ 1042
Neutron star
ADM
Thermal
BEC
Thermal
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ADM in Neutron StarsStep 4: Self-gravitating
Step 5: Gravitational Collapse
ADM is heated up, but will be cooled down again by neutrons
When the ADM density is higher than the neutron density, ADM becomes self-gravitating
rBEC ∼ 3× 10−5 cm
rth ∼ 76 cm
Rns 10.6 km
Thermal
BEC
Thermal
BEC
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Form a Mini Black HoleStep 6: Overcome zero point energy
A mini black hole forms !
Recall
Chandrasekhar limit for bosons
Only if ADM can collapse to a black hole
Note
E ∼ −GNm2
R+
1
R< 0 N boson
Cha ∼ 1.5× 1036
NfermionCha ∼ 1.8× 1054
NBECX > N boson
Cha
NBECX = N total
X −N critX ∼ 1042
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Hawking Radiation
Eating baryons Hawking radiation
The black hole will destroy the host star if its initial mass is larger than
dMBH
dt= 4πλs
GMBH
v2s
2
ρBvs −1
15360πG2M2BH
M crit
BH 1.2× 1037 GeV
⟿⟿
⟿⟿
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Limits from Neutron Stars• Observed old neutron stars set an upper bound
on DM-neutron scattering cross section
McDermott, HBY, Zurek (2011)
Capture rate∝σn
The black hole evaporates due to Hawking radiation
In the shaded regions, bounds are lifted
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Beyond the WIMP Paradigm• Hidden sector dark matter
• An example: hidden charged dark matter
nightmare scenario?
e
e
e
ePhoton
Visible
XX
X XPhoton
HiddenαX =?αem =
1
137
YES NOCan we still understand dark matter?
Feng, Tu, HBY (2008); Feng, Kaplinghat, Tu, HBY (2009)
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Self-interacting Dark Matter• Self-interactions can affect dark matter dynamics
Morphology:randomize the dark matter velocity dispersion; lead to spherical halos and clusters
Self-interacting dark matter may behave as hot gas
Markevitch et al. (2003);Clowe et al. (2006)
gasDM
DM
Bullet Cluster
Spergel, Steinhardt(1999); Miralda-Escude (2000)Dave et al. (2001); Yoshida et al. (2001); Feng, Kaplinghat, Tu, HBY (2009); Feng, Kaplinghat, HBY (2009)
Star
gas
star
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Limits on the Hidden Charge
XX
X X
Photon
Hidden
αX =?
Feng, Kaplinghat, Tu, HBY (2009)
Excludedαem
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Small Scale Structure and SIDM
• Self-interacting DM is actually motivated to solve the small scale structure problem of collisionless cold DMSpergel, Steinhardt (1999)...
X
X
X
X
Vogelsberger, Zavala, Loeb (2012) Rocha, Peter, Bullock, Kaplinghat, et al. (2012)Peter, Rocha, Bullock,Kaplinghat (2012)
σT /mχ ∼ 0.1− 10 cm2/g
σT ∼ 10−36 cm2 WIMP
1 cm2/g ∼ 2× 10−24 cm2/GeV
Recent simulations suggest
r/rs
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SIDM with a Yukawa Potential
Tulin, HBY, Zurek (2012)
XX
X X
ɸ
Feng, Kaplinghat, HBY (2009)Loeb, Weiner (2010)
σT ≈ 5× 10−23 cm2 αX
0.01
2 mX
10GeV
210MeV
mφ
4
A light mediator is required
• The scattering cross section has a rich structure• In general, σT has a velocity-dependence• It helps avoid constraints from large scales
mx, mɸ,αX
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A Unified Model
XX
X X
ɸ
ɸ
ɸX
X
• For a given dark matter mass, we fix the coupling constant by the correct relic density• We map out the parameter space (mx, mɸ) required to solve the small scale structure problem
DM self-scattering and the relic density are usually considered separately
Fix αX
σT ∼ 0.1− 10 cm2/gTulin, HBY, Zurek (2012)
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Self-interacting Dark Matter
Tulin, HBY, Zurek (2012)contours (cm2/g)
The blue regions are preferred by the simulations to solve the small scale structure problem
X-X, X-X_
X-X
σAv 6× 10−26 cm3/s
σT /mX
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Summary
• Cosmological/Astrophysical observations cry out for new physics beyond the Standard Model
• WIMPs are well-motivated dark matter candidates and the WIMP paradigm is very predictive
• Both the Tevatron and the LHC are probing the dark sector
• Different search strategies are available for dark matter beyond the WIMP paradigm
• We are in an exciting data-driven era
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Self-interacting Dark Matter• In usual WIMP models, self-scattering cross
sections are too small to play a role in galactic dynamics
• Self-interacting DM is motivated to solve the small scale structure problem of collisionless cold DM
Vogelsberger, Zavala, Loeb (2012)
Spergel, Steinhardt (1999)...15 most massive subhalos
X
X
X
X
X
X
SM
SM
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“Too Big to Fail”Boylan-Kolchin, Bullock, Kaplinghat (2011)
Vogelsberger, Zavala, Loeb (2012) Rocha, Peter, Bullock, Kaplinghat, et al. (2012)Peter, Rocha, Bullock,Kaplinghat (2012)
The problem can be solved by SIDM
σT ∼ 10−36 cm2WIMP1 cm2/g ∼ 2× 10−24 cm2/GeV
σT /mχ ∼ 0.1− 10 cm2/g