Superstring Theory

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Superstring Theory

• Paul J. Thomas
• Department of Physics and Astronomy
• UW-Eau Claire

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What is String Theory?

• We want a unified theory of all forces.
• We want a quantum theory of gravity.
• Why?
• all the other forces have quantum theories.
• we know spacetime is quantized for small
  distances.

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The Planck Length

• The smallest length for which classical
  space-time (e.g. General Relativity) will work.
• 1.6 ?10-35 m 10-20 ? proton diameter.
• On this scale, space-time is turbulent, with
  spontaneous creation and destruction of many
  virtual particles.

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Spacetime Foam
Kip Thorne, Black Holes and Time Warps
Einsteins Outrageous Legacy, 1994
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String Theory

• General Relativity fails really badly when point
  particles interact.
• So lets consider matter to be made up of tiny
  loops of matter, a Planck length long.

?10-35 m?
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String Theory

• This solves the problems!
• Oh, and we need 10 dimensions of spacetime to
  make the math work (or 11, or 26).
• But all but 4 of these can be curled up tight
  inside the Planck length

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Why Superstrings?

• Original string theory only worked for bosons
  (e.g. photons and mesons), not fermions (e.g.
  electrons and protons).
• Theory needed to be combined with Supersymmetry.

Six-dimensional Calabi-Yau shapes at each point
in spacetime
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What is Supersymmetry?

• A unified theory for the strong, weak and
  electromagnetic forces.
• Predictions
• electromagnetic and weak forces merge to form one
  force at 1015 K (confirmed).
• electroweak force merges into strong force at
  1028 K.

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More Supersymmetry Predictions

• Fermions
• spin ½ particles
• e.g. protons, neutrons, electrons, quark
• make up matter
• Bosons
• spin 0,1,2 particles
• e.g. photons, mesons, gluons, W particles
• virtual particles for forces
• Every known particle should have a superpartner
  with spin ½.

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Superpartners

• So a quark (spin ½) should have a squark partner,
  (spin 1).
• A photon (spin 1) should have a photino partner
  (spin 1½).

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What is M-Theory?

• M-Theory is the most current name for superstring
  theory.
• Nobody is willing to say what M stands for!
• It could mean
• Membrane (an n-dimensional surface)
• Manifold (a set of Membranes)
• Mystery
• Mother of all theories

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I know! You want the full story

• My theme here will be to suggest that we should
  somehow study D-branes with N ? , with tachyon
  condensation to annihilate most of the branes and
  reduce to something more manageable. To motivate
  this, I will consider two concrete questions that
  seem to require taking the number of D-branes to
  be infinite. One question is the relation of Type
  IIA superstrings to K-theory the other is the
  inclusion of a topologically non-trivial NS
  three-form field H in the K-theory classification
  of RR charges and fields.
• Ed Witten, Overview of K-Theory Applied To
  Strings, Int.J.Mod.Phys. A16 (2001) 693-706.

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Alright! Where can I go next?

• Try
• superstringtheory.com
• Brian Greene, The Elegant Universe
• http//www.pbs.org/wgbh/nova/elegant/

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Is there any hope we can test this?

• At Fermilab, Maria Spiropulu hopes to see
  particles disappearing into an extra dimension.
  In some experiments, a proton and antiproton may
  collide, producing a graviton, which mediates the
  gravitational force. The graviton may sail off
  our universal "brane" into the fifth dimension,
  leaving behind a tremor in our ordinary reality.