Inflation: particle physics models

1
Inflation particle physics models

• Motivation for and status of inflation
• Slow roll inflation
• Hybrid Inflation
• Structure formation and CMB
• Curvaton approach
• Realistic hybrid inflation model
• Large scale structure from Higgs
• Extra dimensions and D-brane inflation

2
Motivation for Inflation

• Horizon problem
• Flatness problem
• Relic removal
• Structure formation
• Present universe is inflating

3
How inflation solves the horizon problem
Physical scale
time
Horizon crossing
4
Status of Inflation
Observation
Prediction

• Observed Flatness
• Observed perturbations
• 3 peaks observed
• No evidence for non-Gaussianity
• CMB measures
• Gravity waves not observed

• Flatness
• Density perturbations
• Acoustic peaks expected
• Gaussian
• Spectral index
• Gravity Waves

5
Polarisation
DASI 2002

• CMB at last scattering surface is expected to be
  polarised (just like reflected sunlight)
• Polarisation probes gravity waves
• Gravity waves excite B-mode (curl) of
  polarisation that density perturbations cannot
• Planck will improve current limit by 50 times
• DASI made first observation of polarisation last
  year

6
New Inflation (Linde, Albrecht,Steinhart, 1982,)
Old Inflation (Guth 1981)
False-vacuum tunnels to true vacuum due to first
order phase transition. Bubbles of true vacuum
grow due to negative pressure. FAILS SINCE
INFLATION NEVER ENDS!
False-vacuum slowly rolls towards the true vacuum
several mechanisms possible for ending
inflation. ? SLOW ROLL INFLATION -- THIS TALK
7
Slow roll inflation

• slow roll in a false vacuum generates
  accelerated expansion in the very early universe

Slow roll parameters
8
see, e.g., Lyth Riotto
Types of slow roll inflation
High energy, not-so-slow roll 1.Large field
chaotic inflation Lower energy, very slow
roll 2. Small field new inflation 3. Hybrid
inflation
Single-field models
Multi-field models
9
Linde 90
Hybrid inflation

• Involves two (or more) scalar fields slowly
  rolling inflaton plus other fields
  which are destabilised when reaches a
  critical value
• Reheating occurs when fields oscillate about
  global minimum
• Uses flat potentials expected in SUSY, SUGRA
• Predicts negligible gravitational waves

10
Structure formation

• Usual lore quantum fluctuations of inflaton is
  seed of structure

freezes in as a classical perturbation
curvature perturbation
(stays constant from horizon crossing to re-entry)
11
CMB measurements
Spectrum
This provides a very strong restriction on the
inflaton potential which may be relaxed if the
inflaton is not responsible for curvature.
12
Lyth, Wands, Ungarelli,K.Dimopoulos,Bartolo,Liddle
,.
The curvaton approach

• Late decaying (curvaton) scalar gives large
  isocurvature perturbations
• Inflaton gives small curvature and decays into
  radiation
• Isocurvature perturbations ? curvature
  perturbations before re-entry

Entropy -- isocurvature

• Initially and
  so
  
• Then and
  until

• This relaxes the COBE constraint on the inflaton
  potential!

13
Bastero-Gil,SFK
Realistic hybrid inflation model
NMSSM type Superpotential
Higgs
Potential (Higgs0)

• Generates SUSY Higgs mass
  at the end of inflation
• Axionic solution to strong CP problem with
• Naturalness problems
  
• Slow roll requires only but
  COBE
• We can use Higgs isocurvature perturbations to
  generate structure ?

14
Bastero-Gil, Di Clemente, SFK
Large Scale Structure from the Higgs Fields

• D-flat direction

• Higgs slow roll during inflation

• Initially

• Isocurvature Higgs perturbations transferred to
  curvature perturbations at start of reheating
  when energy densities become comparable

• Non-Gaussianity below Planck sensitivity

N.B. Higgs decays quickly unlike curvaton

• Relic isocurvature perturbations?

• Spectral index

15
Bastero-Gil, Di Clemente, SFK
Extra Dimensions and Naturalness

• Extra dimensions have been considered in
  inflation models in different contexts
• We focus on their application to the naturalness
  problems of realistic model
• Put Higgs and singlets in bulk, matter fields on
  brane
• Set string scale and SUSY
  breaking scale

• Extra dimensions solves ALL naturalness problems
  of the model

• Vacuum

• Couplings

• Brane mass

• Bulk mass

16
Dvali, Tye, Shiu,Burgess,Cline
Sen
D-brane Inflation
Tytgat,Sami,Jassal

• Brane-antibrane at large separation attract each
  other and annihilate
• The separation acts as an inflaton field with
  effective potential
  
• When the separation string length branes
  annihilate, and have tachyon condensation which
  ends inflation rather like hybrid inflation
• All energy goes into tachyon potential
  - reheating of our brane?
  

17
Prospects and Conclusions

• MAP in 2 weeks!! e.g. angular power spectrum to
  l900
• Planck launched in 2007, extend out to l3000,
  measure polarisation
• MAPPlanck measure
• Inflation is a paradigm in search of a model
  more work is required to relate inflation to
  particle physics and string theory
• Inflation could have happened at several
  different energy scales (it is happening today)
  but only the lowest scale is relevant for
  observation
• Hybrid inflation at intermediate scale looks most
  relevant for particle physics, and provides a
  link with the SUSY standard model
• Perturbations need not arise from inflaton (e.g.
  curvaton, Higgs,)
• Each inflation model makes testable predictions,
  so new data can rule out models, and help lead to
  a standard model of inflation