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Supersymmetry

The Coming Revolutions in Particle Physics

Hitoshi Murayama (UC Berkeley)

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Introduction

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20th Century Physics

• Two great discoveries of 20th cent. physics:– Quantum Mechanics– Einstein’s Special Relativity (Electromagnetism)

• Marriage between the two

Existence of Anti-matter

doubled #particles– Positron (anti-particle of electron) 1932– Anti-proton 1955 (Bevatron, Berkeley)

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21st Century Physics

• Marriage of Quantum Mechanics and Gravity (Einstein’s General Relativity)

Existence of Super-matter

Double #particles again

• Photino (superpartner of photon) 2004?

• Selectron (superpartner of electron) 2010?

Supersymmetry

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Outline

• Introduction

• Anti-Matter

• Weak Force and God Particle

• God Particle’s Problem

• Supersymmetry

• Conclusion

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Anti-Matter

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Matter & Anti-Matter Annihilate!

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Why was Anti-Matter Needed?

• At the end of 19th century: a “crisis” about electron– Like charges repel: hard to keep electric charge

in a small pack– Electron is point-like– At least smaller than 10-17 cm

• Need a lot of energy to keep it small!

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E=mc2

• Need more than 109 eV of energy to pack electric charge tightly inside the electron

• But the observed energy of the electron is only 5 105 eV

• Electron cannot be smaller than 10–13 cm??

• Breakdown of theory of electromagnetism

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Uncertainty Principle

• Energy-Time Uncertainty Principle:

You can violate energy conservation if it is only for a short time

• Vacuum is full of quantum bubbles!

Werner Heisenberg

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Anti-Matter Helps

• Electron creates a force to repel itself

• Vacuum bubble of matter anti-matter creation/annihilation

• Electron annihilates the positron in the bubble

only 10% of mass

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Anti-Matter Helps

• “Anti-matter attraction” cancels “Like-charge repulsion”

• It does not cost too much energy to tightly pack the electric charge inside the electron

• Needed anti-matter: double #particles

• Theory of electromagnetism now works at very short distances (12 digits accuracy!)

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Weak Force and God Particle

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Mystery of the “weak force”

• Gravity pulls two massive bodies (long-ranged)

• Electric force repels two like charges (long-ranged)

• “Weak force” pulls protons and electrons (short-ranged) acts only over 10–16 cm [need it for the Sun to burn!]

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Something is in the Universe

• There is something filling our Universe

• It doesn’t disturb gravity or electric force

• It does disturb weak force and make it short-ranged

• What is it??

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The God Particle

• “Higgs Boson” fills our Universe

• It disturbs the weak force so that it cannot act very far

• We are sure it exists. But nobody has seen it yet

• Mother of all masses

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But soon?

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Fermi’s dream era

• Fermi formulated the first theory of weak force (1933)

• Knew the required energy to study the problem: 1012 eV

• We are finally getting there!

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God Particle’s Problem

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Higgs repels itself, too

• Just like electron repeling itself because of its charge, Higgs boson also repels itself

• Requires a lot of energy to contain itself in its point-like size!

• Breakdown of theory of weak force

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But there is gravity

• Gravity and quantum mechanics unify at an extremely short distance 10–33 cm

• Higgs boson must be this small, too, to have a sensible unified theory of gravity and quantum mechanics

• But current theory of weak force breaks down already at 10–17 cm

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Supersymmetry

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History repeats itself?

• Double #particles again superpartners

• “Vacuum bubbles” of superpartners cancels the energy required to contain Higgs boson in itself

• Theory of weak force made consistent with unification of gravity and quantum mechanics

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Einstein’s dream

• Forces with very different strengths: electromagnetism, strong, weak forces

• Strengths change at different distance scales

• They become equal: share the same origin

“Grand Unification”

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Where are the superpartners?

• They need to cancel self-repelling energy of the Higgs boson

• Cannot be too heavy to do this job

• Have to be below 1012 eV or “Fermi energy”

• We are getting there this decade– Tevatron (Fermilab, Illinois) 2001–– LHC (CERN, Switzerland) 2006–

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Superpartners everywhere?

• There are unknown “Dark Matter” in our galaxy and outside

• It amounts for about 30% of the Universe

• Lightest superpartner one of the best candidates

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Superpartners as probe

• Most exciting thing about superpartners beyond existence:

They carry information of small-distance physics to something we can measure

e.g., “Is Grand Unification true?”

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Conclusions

– We are finally reaching “Fermi’s dream era”– We will know what is disturbing the weak force,

and generating all masses soon– To make Higgs boson contain itself without

needing too much energy, we need supersymmetry

– Superpartners are within the reach this decade– They bring more information about ultimate

short-distance physics

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