The physics of inflation and dark energy

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The physics of inflation and dark energy
2.6 Acceleration in scalar field models
Equation of motion
small

• Canonical scalar fields

If the
kinetic
energy gt slow roll
With slow- roll, f works like a
"time- dependent" L V(f) lt--gt L
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The physics of inflation and dark energy
2.7 Starting and stopping a slow-rolling scalar
field
V(f)

• Inflation is easy to start just prepare the
  scalar field somewhere, and "let it roll". If its
  energy rf is not negligible, then it will
  quickly dominate, and the slow-rolling scalar
  field will cause spacetime to inflate.

f

• But... not so good for dark energy since rF
  is nearly constant, there is usually a fine
  tuning problem with the the scalar field (as
  happens with L .)
• gt it is very hard to adjust F and V(F) such that
  rF dominates the energy density at just the
  right time (z1) !

! Hard to turn on at right time !
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The physics of inflation and dark energy
2.8 Dark energy - a theorists viewpoint
Coincidence Problem!!!

• Cosmological Constant w - 1

Fine tuning
Coincidence Problem!!!

• Barotropic dark energy wX const.

Fine tuning

• Tracking dark energy w w(t)

Self-adjusting (?)
1z a0/a
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The physics of inflation and dark energy
2.9 The modelling battlefield
Canonical ("honest-to-God") scalar fields

• V(f)m4 exp-a f Wetterich 1988
• V(f)m4a f-a Ratra Peebles 1988
• V(f)m4 cos(f/f0)1 Frieman et al 1995
• V(f)m4 coshf/f0 Chimento Jakubi 1996
• V(f)m4a f-a expk f2 Binétruy 1998, Martin
  et al 1998
• V(f)m4 expa/f Steinhardt et al 1998
• V(f)m4 1-(f-f0)2 exp-a f Albrecht
  Skordis 1995
• V(f)whatever many many authors

Very common attractor behavior for the
background (Ferreira Joyce 1998,Brax et al.
2000) and for the perturbations (Abramo Finelli
2000) gt results independent of the initial
conditions!
Other models

• rf (f)2/(1afbf) (K-essence) Armendáriz-Pi
  cón et al 2001
• rf V(f)/1-(dµf)2 (Tachyon) Sen 2002,
  Padmanabhan 2002
• p -A/ra (Chaplygin gas) Kamenshchick et al.
  2001, ...
• ??? (Branes) many many many many many

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The physics of inflation and dark energy
Dark energy models - pros and cons
Pro
Con

• Easy to parametrize
• Cosmolog. quantities are simple expressions
• Observations so far only sensitive to w, not dw/dt

• Fine tuning
• No good motivation (except for pure L)

• Barotropic, wXconst.
• (Ex L , wL - 1)

• Still, some fine tuning!
• Often not really well-motivated at all
• Cant resolve time dependence of w

• Easy to model
• (Maybe) physically well-motivated
• Fair hope of explaining coincidence problem.

• Scalar field , ww(t)

• Other models K-essence, "rolling tachyon",
  Chaplygin gas, "vacuum metamorphosis", ... ?

? ? ?
? ? ?
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The physics of inflation and dark energy
3. Inflations greatest achievementparticle
creation and the origin of everything
QUANTUM MECHANICS " DE Dt gt h/2p " The
vacuum is filled with virtual pairs of
particles, which exist for very brief moments,
before being annihilated back to nothingness.
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The physics of inflation and dark energy
3.1 Virtual pairs and particle creation
Right here, right now
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The physics of inflation and dark energy
3.2 Virtual pairs in an accelerating background
Horizon H-1
Inflation (acceleration) converts virtual pairs
into real pairs
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The physics of inflation and dark energy
3.3 From quantum fluctuations to galaxies
Andromeda
Thats us
10-35 s
10-33 s
1.5 1010 y
3. 105 y
(Adapated from Lineweaver 1997)
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The physics of inflation and dark energy
Past light cone of an astronomer on Earth
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The physics of inflation and dark energy
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The physics of inflation and dark energy
Conclusions

• There is an impressive amount of observational
  evidence suggesting that the Universe has
  suffered two phases of acceleration one in the
  very early Universe (inflation, t10-35 s), and
  the other right about now (Dark energy age,
  t1010 years)

• The two phases appear to be completely unrelated
  what works for one, does not seem to work for the
  other

• The evidence for dark energy is persuasive and
  growing, but is still shaky. The case is not as
  solid as for inflation (yet)

• At present, nearly all dark energy models are
  contrived, fine-tuned and degenerate - in short,
  bad and ugly

• The physics of inflation use, in a very deep way,
  both Quantum Mechanics and General Relativity -
  and the consequences are fully consistent with
  observations!

• Inflation will never be "confirmed" either the
  evidence will be consistent with it, or not. Must
  learn to live with that...