Better Than Fiction:

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Better Than Fiction questions in fundamental
physics
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Questions from the Standard Model Why so many
free parameters? (16 masses, 11 couplings) Why 3
generations? Why 3 forces? (U(1)xSU(2)LxSU(3)
unification) Why fermions and bosons?
(SuperSymmetry) Questions from the Weak
sector What is special about weak
interactions? What is special about the
Higgs? Why are neutrinos so light? Questions
from the 5th dimension What about gravity? Why 4
dimensions? What lies beyond/beneath? (string
theory) Questions from the Heavens What is the
history of the universe? Why is the universe
flat? What is dark matter? Why is the universe
dominated by matter? (source of CPV) What is dark
energy? What was the big bang?
A Small Sample of Fundamental Questions
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The Standard Model contains 16 masses 11
couplings as free parameters
Why these particles?
Why these masses?
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History of Unification
electric
magnetic
planets
atoms
apple
electromagnetiesm
Quantum mechanics
gravity
mechanics
g-decay
Special relativity
b-decay
GR
QED
a-decay
Electroweak theory
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The idea The U(1)xSU(2)xSU(3) transformations
form a subgroup of a larger group of
transformations just like rotations form the
subgroup SO(3) of Lorentz transformations, which
include rotations and boosts.
Grand Unification

• At low energy, the ground state breaks the full
  symmetry of the transformations.
• This implies new force mediators to retain gauge
  invariance under the new transformations.

Convergence of couplings at high energy suggests
they might all come from one general force.
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Supersymmetry (SUSY)
The Idea Every known particle has a (high mass)
superpartner with different spin. Spin 1/2
particles have partners of spin zero, spin 1
particles have partners of spin 1/2. This
provides a natural balance between fermions and
bosons.
Advantages Fixes running coupling constants so
they match at high energy. Needed by superstring
theory to include fermions in string
theory. Helps explain low Higgs mass.
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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 1016 cm

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Something is in the Universe

• There is something filling our Universe
• It doesnt disturb gravity or electric force
• It does disturb weak force and make it
  short-ranged
• What is it??

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Higgs Boson is Most Likely Just Around the
Corner

• Current data combined with the Standard Model
  theory predict
• mHlt196GeV (95CL)
• Tevatron at Fermilab has a chance to discover or
  exclude the SM Higgs boson by 2008

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Neutrino Oscillations and Masses
Interesting fact When SN1987A blew up, the
output in neutrinos was 1046 Watts. The visible
light output of the entire rest of the universe
is 1045 Watts.

• The current belief
• Solar ne disappear because ne ?nm.
• Atmospheric nm disappear because nm ?nt.

• Consequences
• Neutrino oscillations imply non-zero neutrino
  masses (remember the mixed states have different
  masses and lifetimes from the unmixed states).
• Neutrinos contribute to CPV via a neutrino CKM
  matrix,

• Neutrinos contribute to the mass energy of the
  universe.

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Neutrino Production in the Sun
Light Element Fusion Reactions
p p ?2H e ?e
99.75
p e- p ? 2H ?e
0.25
10-5
3He p ?4He e ?e
7Be e- ?7Li ?e
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8B ? 8Be e ?e
0.02
Bottom line NOT ENOUGH NEUTRINOS DETECTED
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Atmospheric n are produced from the decay of ps
and ms. Expect nm 2 ne.
Look for nm as a function of azimuth via the
reaction
Bottom line nm are disappearing
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The Essentials of Superstring Theory
The idea

• So-called fundamental particles are actually
  vibrating strings of Planck length 10-33 cm.
  Different particles (fermions and bosons) are
  just different vibrational modes.

• Fermions can be included if the theory is
  supersymmetric.
• Negative probabilities are avoided if strings
  are allowed to vibrate in 10 dimensions.

• Divergent integrals dont arise since none of the
  interactions are pointlike no need for
  renormalization.

• Extra 6 dimensions are curled into a particular
  Calabi-Yau space (of many possible).
• The geometry and size of these extra dimensions
  determines masses and charges of particles (and
  number of holes number of generations).

A 2D cross section of a 6D Calabi-Yau space
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Fluctuations in the CMB have a characteristic
size dependent on trecom and vsound. The
apparent size of the fluctuations measures the
curvature of spacetime. The curvature tells us
about the total energy density from
Bottom line The universe is flat!
Bennett et al 2003
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Dark Matter

• Amount of matter in galaxies can be determined
  from rotation curves
• Galaxy is held together by mass far bigger than
  all stars

• Known baryonic matter accounts for 5 of the
  universe
• 23 of the universe is made of weakly
  interacting heavy stuff not comprised of known
  particles
• 73 is comprised of non-attractive energy

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Observations of distant supernovae measure the
acceleration of the universe.
Apparent brightness measures how long the light
has been travelling (and spreading
out). Redshift measures the expansion of the
universe during that time.
accelerating universe
The universe is expanding faster now than it
used to!!!
decelerating universe
Riess et al. (1998) Perlmutter et al. (1999)
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Dark Energy
We know of one type of energy that could cause
acceleration -- vacuum energy. Normal matter
becomes less dense in an expanding universe,
leads to falling pressure, slower
expansion. Vacuum energy density remains
constant the extra pressure drives expansion.
vacuum energy bubble
Popularly known as the worst prediction in
theoretical physics!
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Appendixes
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Baryon AsymmetryEarly Universe
10,000,000,001
10,000,000,000
n.b. CP violation from SM appears too small to
explain this.
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Baryon AsymmetryCurrent Universe
us
1
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• Key ingredients of electroweak theory
• Doublet of fermions invariant under phase U(1)
  and SU(2) transformations implies 4 gauge fields
  which couple to fermions via covariant derivative
• Doublet of complex Higgs with broken symmetry
  leads to one massive real Higgs field and 3
  Goldstone bosons
• If Higgs doublet is invariant under same
  transformations as fermion doublets (i.e. couples
  to same gauge fields) then a gauge transformation
  can always remove the Goldstone fields and
  replace them with mass terms for 3 of the gauge
  fields.

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• The problem with quantum gravity
• Gauge invariance only invents vector spin-1
  particles, not tensor spin-2 particles.
• Divergent graphs are much worse than logarithmic
  for spin 2 (in fact diverge like q4J-8D ) and
  are not renormalizable.
• String theory avoids the divergence because the
  high energy limit is not the same as small
  distance. Minimal distance is determined by
  string size.