Grand Unification and Proton Decay

1
Grand Unification and Proton Decay

• Sean Caruso
• Henry Greenberg
• Ian Lofgren

2
Forces

• Standard Model
• Strong Interaction
• Electromagnetism
• Weak Interaction
• Newtonian Mechanics/ General Relativity
• Gravitation (also has a particle representation)

3
Quarks

• Along with leptons are elementary particles.
• Six flavors up, down, charm, strange, top, and
  bottom.
• All but up down are highly unstable.
• Up down distinguished by their charge.
• Up 2/3
• Down -1/3
• Generally found in groups of 2 (mesons) and 3
  (baryons)

4
Quarks (cont.)

• Make up protons neutrons
• Proton 2 up, 1 down
• Neutron 1 up, 2 down
• Only elementary particle that interacts with all
  four fundamental forces.

5
The Strong Force

• Represents interactions between quarks and
  gluons.
• Gluons are the mediators of the Strong Force.
• Very short range 10-15 m
• Strong enough to hold protons together in the
  nucleus.

6
Electromagnetism

• Magnetic and electric forces involve the exchange
  of photons.
• Seen through forces between charges and the
  magnetic force.
• Holds atoms and molecules together
• Determines structure
• 1/137 as strong as the Strong Force
• Infinite range which obeys the inverse square law.

7
The Weak Force

• Carriers are the heavy W and Z bosons.
• Responsible for phenomena at the scale of the
  atomic nucleus.
• Most familiar effect is beta decay.
• Only interaction capable of changing flavor.
• Strength is 10-6 times the Strong Interaction.
• However, can act between leptons.

8
The Weak Force (cont.)

• Even smaller range than the Strong Force
  10-18 m
• There is an inverse relation between the mass of
  the boson and the range of the force.

9
Gravitation

• Particle Physics
• Massless exchange particle is the graviton.
• General Relativity
• A property of spacetime effected by mass.
• Weakest of the fundamental forces.
• Dominant force in shaping the large scale
  structure of galaxies, stars, etc.
• Infinite range, obeying inverse square law.

10
Supersymmetry Primer

• Supersymmetry interchanges particles of
  completely dissimilar types.
• fermions (such as electrons, protons and
  neutrons)
• Fermions are inherently the individualists and
  loners of the quantum particle world no two
  fermions ever occupy the same quantum state.
  Their aversion to close company is strong enough
  to hold up a neutron star against collapse even
  when the crushing weight of gravity has overcome
  every other force of nature. -Jan Jolie,
  Scientific American July 2002
• bosons (such as gluons, photons, W and Z heavy
  bosons)
• Bosons readily gather in identical states.
• Supersymmetry somehow connects fermions and
  bosons.
• For supersymmetry to occur undiscovered partners
  of currently known particles would need to exist.

11
Gauge Symmetries

• The Standard Model is a theory of electromagnetic
  and weak interactions
• based on relativistic quantum gauge field theory
• The gauge field is a mathematical (unitary)
  representation of the symmetries in forces.
• U(1) refers to electromagnetism
• SU(2) refers to the weak interaction
• SU(3) refers to the strong interaction
• Poor gravity it doesnt get one
• Number of Bosons in a Unitary group n goes as n2
  - 1
• The Higgs field results from the necessity to
  assign mass that can vary.

12
Electroweak Unification

• Electromagnetism and the weak force appear to
  unify at roughly 1011 eV or at distances less
  than 10-17 m.
• Electroweak Unification is SU(2)xU(1), providing
• three massless gauge bosons from SU(2) which
  become massive as a result of the Higgs field
• one boson from U(1) which is the photon
• The experimental success of this idea has led
  physicists to extend it to higher energies and
  possible higher symmetries.

13
Grand Unification

• The unification of the electromagnetic, weak and
  strong forces
• Represented by SU(3)xSU(2)xU(1)
• Occurs at roughly 1024 eV
• This is significantly larger than we can obtain
  with accelerators
• Observable early in the life of the Universe

14
Grand Unification (cont.)

• Weak and Strong forces become weaker at higher
  energy levels
• Electromagnetic becomes stronger at higher energy
  levels
• At unification, various particles are capable of
  changing type

15
Supersymmetry and Grand Unification

• Exchanges Bosons and Fermions
• Bosons have no limit on states
• Fermions are limited in states
• Grand Unification predicts forces become
  equivalent at some point
• Without supersymmetry the three forces do not
  meet at one point

16
Supersymmetry and Grand Unification (cont.)

• A supersymmetric theory should not violate any of
  the conservation laws of particle interactions.
• However, it can occur in combination with grand
  unification.
• The proton is the lightest baryon and hence, if
  baryon number is conserved, the proton should be
  extremely stable
• Baryon number is baryons - anti-baryons
• Supersymmetry predicts that baryon and lepton
  number violations occur less frequently

17
Proton Decay

• Grand Unification allows quarks to couple to
  leptons
• two quarks can be converted into an anti-quark
  and an anti-lepton
• For example, two up quarks would be allowed to
  turn into a positron and a down anti-quark.
• A proton consists of two up quarks and a down
  quark
• A neutral pion is a down quark and a down
  anti-quark
• Therefore if the two up quarks become close
  enough for Grand Unified forces to act, the
  proton will decay into a positron and a neutral
  pion

18
Proton Decay (cont.)

• Originally Grand Unified Theories, without
  supersymmetry, predicted the proton half-life to
  be 10282 years
• Grand Unified Theories with supersymmetry predict
  the proton half-life to be 1032 years
• This is one of the few ways to detect unified
  forces at low energies

19
Proton Decay (cont.)

• Built proton decay detectors in Cleveland and
  Japan
• The Cleveland detector is gone.
• The Japanese detector broke.
• Komiokande detector
• 3000 tons of water, 1000 photo receptors
• 50000 tons of water 11146 photo receptors
• No proton decays have yet been detected

20
Cosmology

• What does this have to do with the big bang?
• Particle physics currently assume no violations
  of baryon number
• Somehow in the early universe more matter, rather
  than anti-matter was created
• For matter to be created faster implies that the
  baryon number was violated early in the universe

21
Bibliography

• Horgan, John. Particle Metaphysics. Scientific
  American February 1994
• Jolie, Jan. Uncovering Supersymmetry. Scientific
  American July 2002
• Weinberg, Steven. A Unified Physics by 2050.
  Scientific American December 1999
• Supersymmetry to the Rescue? www.superstringtheory
  .com/experm/exper4a.html
• Unification and distance scales.
  www.superstringtheory.com/experm/exper3a.html
• Super Kamiokande. neutrino.phys.washington.edu/su
  perk