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Theoretical Particle Physics:Beyond the Standard Model
Jonathan Feng
UC Irvine
UCI Pizza Talk
18 April 2003
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The Standard Model
Carrier Force Mass
photon E&M 0
g gluon Strong 0
Z
WWeak
91 GeV
80 GeV
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Tevatron
Precise Confirmation
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Why is Mweak so small?
• How big should it be? We know of only three constants:– Special relativity: speed of light c
– General Relativity: Newton’s constant GN
– Quantum mechanics: Planck’s constant h
• From these we can form– Planck time: tPl ~ 10-43 s
– Planck distance: lPl ~ 10-33 m
– Planck mass: MPl ~ 1019 GeV
• Why is MWeak so small compared to MPl ?
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Solution 1: Symmetry
• Photon is light, but this doesn’t bother us, because it is massless because of a symmetry
• There is only one symmetry that can explain the weak scale: supersymmetry (SUSY)
• Predicts a partner particle for every known particle
Soap BubbleStandard
Model
Large parameter
Length L
Height HMPl
Small parameter
L H Mweak
Symmetry explanation
Rotational invariance
SUSY
Prediction
Particles traveling in
different directions
Particles with different spin
Symmetry Breaking
GravitySUSY
breaking
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Prediction of Supersymmetry
• Supersymmetry predicts new particles with masses ~ 1 TeV
• If SUSY is right, these will be discovered at the Large Hadron Collider (~2008) or in other experiments
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Solution 2: Extra Dimensions
• Maybe GN isn’t what we thought it was
• MPl is very large because GN is very small, that is, gravity is very weak
For protons, gravity is 10-36 times weaker.
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Extra Dimensions
• But suppose gravity propagates in n extra dimensions of size L:
For r L, Fgrav ~ 1/r2
For r L, Fgrav ~ 1/r2+n
Garden Hose
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…
gravity
EM
Str
engt
h
r1/mstrong
Gravity in Extra Dimensions
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Strong Gravity at the Weak Scale
• Suppose mstrong is at the weak scale
• The number of extra dims n then fixes L
• n=1 excluded by solar system, but n=2, 3,… are allowed by tests of Newtonian gravity
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Tests of Newtonian GravityS
tren
gth
of D
evia
tion
Rel
ativ
e to
New
tona
in G
ravi
tyLong, C
han, Price; H
oyle et al.
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• Black holes can be
created if
ECOM > mstrong
• In 4D, mstrong ~ 1018 GeV, far above accessible energies ~ TeV
• But with extra dimensions, mstrong ~ TeV is possible, can create micro black holes in elementary particle collisions!
Prediction of Extra Dimensions
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Micro Black Hole Events
• Black holes decay through Hawking evaporation
De Roeck (2002)
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Auger Observatory
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AMANDA/IceCube
• Neutrino telescopes may also detect BHs:
contained jets
through-going muons
• Rates of ~10 BH/year
Cosmic rays provide first chance to see black holes, discover extra dimensions
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Conclusions
• There must be new physics at the weak scale
• We will find SUSY, extra dimensions, or something completely unexpected while you are getting your PhD (or during your first postdoc...)
• This will address some profound mysteries, such as force unification, dark matter, quantum gravity, …