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, …