String/Brane Cosmology
-
Upload
lesley-williamson -
Category
Documents
-
view
51 -
download
0
description
Transcript of String/Brane Cosmology
String/Brane Cosmology
…for those who have not yet
drunk the Kool-Aid
with J.Blanco-Pillado, J.Cline, K. das Gupta, C. de Rham, C.Escoda, M.Gomez-Reino, D. Hoover, R.Kallosh,
A.Linde,F.Quevedo, G. Tasinato and A. Tolley
Cosmo 07
On the shoulders of giants
A. Salam, E. Sezgin, H. Nishino,G. Gibbons, S. Kachru E. Silverstein, R. Guven, C. Pope, K. Maeda, M. Sasaki, V. Rubakov, R. Gregory, I. Navarro, J. Santiago, S. Carroll, C. Guica, C. Wetterich, S. Randjbar-Daemi, F. Quevedo, Y. Aghababaie, S. Parameswaran, J. Cline, J. Matias, G. Azuelos, P-H. Beauchemin, A. Albrecht, C. Skordis, F. Ravndal, I. Zavala, G. Tasinato, J. Garriga, M. Porrati, H.P. Nilles, A. Papazoglou, H. Lee, N. Arkani-Hamad, S. Dimopoulos, N. Kaloper, R. Sundrum, D. Hoover, A. Tolley, C. de Rham, S. Forste, Z. Lalak, S. Lavingnac, C. Grojean, C. Csaki, J. Erlich, T. Hollowood, H. Firouzjahi, J. Chen, M. Luty, E. Ponton, P. Callin, D. Ghilencea, E. Copeland, O. Seto, V. Nair, S. Mukhoyama, Y. Sendouda, H. Yoshigushi, S. Kinoshita, A. Salvio, J. Duscheneau, J. Vinet, M. Giovannini, M. Graesser, J. Kile, P. Wang, P. Bostok, G. Kofinas, C. Ludeling, A. Nielsen, B. Carter, D. Wiltshire. C. K. Akama, S. Appleby, F. Arroja, D. Bailin, M. Bouhmadi-Lopez, M. Brook, R. Brown, C. Byrnes, G. Candlish, A. Cardoso, A. Chatterjee, D. Coule, S. Creek, B. Cuadros-Melgar, S. Davis, B. de Carlos, A. de Felice, G. de Risi, C. Deffayet, P. Brax, D. Easson, A. Fabbri, A. Flachi, S. Fujii, L. Gergely, C. Germani, D. Gorbunov, I. Gurwich, T. Hiramatsu, B. Hoyle, K. Izumi, P. Kanti, S. King, T. Kobayashi, K. Koyama, D. Langlois, J. Lidsey, F. Lobo, R. Maartens, N. Mavromatos, A. Mennim, M. Minamitsuji, B. Mistry, S. Mizuno, A. Padilla, S. Pal, G. Palma, L. Papantonopoulos, G. Procopio, M. Roberts, M. Sami, S. Seahra, Y. Sendouda, M. Shaeri, T. Shiromizu, P. Smyth, J. Soda, K. Stelle, Y. Takamizu, T. Tanaka, T. Torii, C. van de Bruck, D. Wands, V. Zamarias, H. Ziaeepour
Cosmo 07
Outline
• Motivation• String Cosmology: Why Does it Make Sense?
• Branes and ‘late-Universe’ cosmology• Some Dark (Energy) Thoughts
• String inflation• A Sledgehammer for a Nutcracker?
• Outlook
Cosmo 07
Outline
• Motivation• String Cosmology: Why Does it Make Sense?
• Branes and ‘late-Universe’ cosmology• Some Dark (Energy) Thoughts
• String inflation• A Sledgehammer for a Nutcracker?
• Outlook
Cosmo 07
Outline
• Motivation• String Cosmology: Why Does it Make Sense?
• Branes and ‘late-Universe’ cosmology• Some Dark (Energy) Thoughts
• String inflation• A Sledgehammer for a Nutcracker?
• Outlook
Cosmo 07
Outline
• Motivation• String Cosmology: Why Does it Make Sense?
• Branes and ‘late-Universe’ cosmology• Some Dark (Energy) Thoughts
• String inflation• A Sledgehammer for a Nutcracker?
• Outlook
Cosmo 07
Strings, Branes and Cosmology
• Why doesn’t string theory decouple from cosmology?
Science progresses because short- distance physics decouples from long distances.
Cosmo 07
Strings, Branes and Cosmology
• Why doesn’t string theory decouple from cosmology?
Science progresses because short distance physics decouples from long distances.
* Inflationary fluctuations could well arise at very high energies: MI » 10-3 Mp
Cosmo 07
Strings, Branes and Cosmology
• Why doesn’t string theory decouple from cosmology?
Science progresses because short distance physics decouples from long distances.
* Inflationary fluctuations could well arise at very high energies: MI » 10-3 Mp
* Cosmology (inflation, quintessence, modified gravity, etc) relies on properties which can be extremely sensitive to short distances.
Cosmo 07
Strings, Branes and Cosmology
• Why doesn’t string theory decouple from cosmology?
Science progresses because short distance physics decouples from long distances.
* Inflationary fluctuations could well arise at very high energies: MI » 10-3 Mp
* Cosmology (inflation, quintessence, modified gravity, etc) relies on properties which can be extremely sensitive to short distances.
* String theory suggests important changes in the low-energy degrees of freedom: branes.
Cosmo 07
Strings, Branes and Cosmology
• Why doesn’t string theory decouple from cosmology?
• Why are branes important for cosmology and particle physics?
D branes in string theory are surfaces on which some strings must end, ensuring their low-energy modes are trapped on the brane.
Polchinski
Cosmo 07
Strings, Branes and Cosmology
• Why doesn’t string theory decouple from cosmology?
• Why are branes important for cosmology and particle physics?
In some cases this is where the Standard Model particles live.
Ibanez et al
Cosmo 07
Strings, Branes and Cosmology
• Why doesn’t string theory decouple from cosmology?
• Why are branes important for cosmology and particle physics?
Leads to the brane-world scenario, wherein we are all brane-bound.
Rubakov & Shaposhnikov
Cosmo 07
Strings, Branes and Cosmology
• Why doesn’t string theory decouple from cosmology?
• Why are branes important for cosmology and particle physics?
Identifies hidden assumptions about low energy theory whose relaxation might help with low energy naturalness problems.
Cosmo 07
Naturalness
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
HHmLSM*2 + dimensionless
Cosmo 07
Naturalness
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
HHmLSM*2 + dimensionless
M ~ 1011 GeV
Mw102 GeV
Mp ~1018 GeV
20
2 mm
BUT: effective theory can be defined at many scales
Cosmo 07
Naturalness
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
HHmLSM*2 + dimensionless
M ~ 1011 GeV
Mw102 GeV
Mp ~1018 GeV
20
2 mm
221
2 Mkmm
BUT: effective theory can be defined at many scales
Cosmo 07
Naturalness
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
HHmLSM*2 + dimensionless
M ~ 1011 GeV
Mw102 GeV
Mp ~1018 GeV
20
2 mm
221
2 Mkmm
BUT: effective theory can be defined at many scales
Hierarchy Problem: These must cancel to 20 digits!!
Cosmo 07
Naturalness
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
HHLSM*2 + dimensionless
Hierarchy problem: Since the largest mass dominates, why isn’t m ~ MGUT or Mp ??
• Three approaches to solve the Hierarchy problem:
Compositeness: H is not fundamental at energies E À Mw
Supersymmetry: there are new particles at E À Mw and a symmetry which ensures cancellations so m2 ~ MB
2 – MF2
Extra Dimensions: the fundamental scale is much smaller than Mp , much as
GF-1/2 > Mw
Cosmo 07
Naturalness in Crisis
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
• The Standard Model’s dirty secret: there are really two unnaturally small terms.
HHmLSM*24 + dimensionless
Cosmo 07
Naturalness in Crisis
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
HHmLSM*24 + dimensionless
me ~ 106 eV
m10-2 eV
mw ~1011 eV
m ~ 108 eV
440
4 mk
4441
4 mkmk ee
Can apply same argument to scales between TeV and sub-eV scales.
Cosmological Constant Problem: Must cancel to 32 decimal places!!
Cosmo 07
Naturalness in Crisis
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
• The Standard Model’s dirty secret: there are really two unnaturally small terms.
HHmLSM*24 + dimensionless
Harder than the Hierarchy problem:
Integrating out the electron already gives too large a contribution!!
Cosmo 07
Naturalness in Crisis
• Dark energy vs vacuum energy
• Why must the vacuum energy be large?
me ~ 106 eV
m10-2 eV
mw ~1011 eV
m ~ 108 eV
Seek to change properties of low-energy particles (like the electron) so that their zero-point energy does not gravitate, even though quantum effects do gravitate in atoms!
Why is this seen………………but not this?
Cosmo 07
Naturalness in Crisis
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
HHmLSM*24 + dimensionless
Cosmological constant problem: Why is ~ 10-3 eV rather than me , Mw , MGUT or Mp?
• Approaches to solve the Hierarchy problem at ~ 10-2 eV?
Compositeness: graviton is not fundamental at energies E À Supersymmetry: there are new particles at E À and a symmetry which ensures cancellations so 2 ~ MB
2 – MF2
Extra Dimensions: the fundamental scale is much smaller than Mp
Cosmo 07
Naturalness in Crisis
• Ideas for what lies beyond the Standard Model are largely driven by ‘technical naturalness’.• Motivated by belief that SM is an effective field theory.
HHmLSM*24 + dimensionless
Cosmological constant problem: Why is ~ 10-3 eV rather than me , Mw , MGUT or Mp?
• Approaches to solve the Hierarchy problem at ~ 10-2 eV?
Compositeness: graviton is not fundamental at energies E À Supersymmetry: there are new particles at E À and a symmetry which ensures cancellations so 2 ~ MB
2 – MF2
Extra Dimensions: the fundamental scale is much smaller than Mp
??
Cosmo 07
• 4D CC vs 4D vacuum energy
• Branes and scales
How Extra Dimensions Help
A cosmological constant
TGgG 8
Cosmo 07
• 4D CC vs 4D vacuum energy
• Branes and scales
How Extra Dimensions Help
A cosmological constant is not distinguishable from a Lorentz invariant vacuum energy
vs
gGTGG 488
TGgG 8
Cosmo 07
• 4D CC vs 4D vacuum energy
• Branes and scales
How Extra Dimensions Help
A cosmological constant is not distinguishable* from a Lorentz invariant vacuum energy
vs
gGTGG 488
TGgG 8
* in 4 dimensions…
Cosmo 07
• 4D CC vs 4D vacuum energy
• Branes and scales
How Extra Dimensions Help
In higher dimensions a 4D vacuum energy, if localized in the extra dimensions, can curve the extra dimensions instead of the observed four.
Chen, Luty & PontonArkani-Hamad et al
Kachru et al,Carroll & Guica
Aghababaie, et al
xtT NMMN2
Cosmo 07
• 4D CC vs 4D vacuum energy
• Branes and scales
How Extra Dimensions Help
These scales are natural using standard 4D arguments.
m ~ mw2/Mp
~ 10-2 eV
H ~ m2/Mp
mw
Cosmo 07
• 4D CC vs 4D vacuum energy
• Branes and scales
How Extra Dimensions Help
These scales are natural using standard 4D arguments.
m ~ mw2/Mp
~ 10-2 eV
H ~ m2/Mp
mw Extra dimensions
could start here, if there are only two of them.
Arkani Hamed, Dvali, Dimopoulos
Cosmo 07
• 4D CC vs 4D vacuum energy
• Branes and scales
How Extra Dimensions Help
Only gravity gets modified over the most dangerous distance scales!
m ~ mw2/Mp
~ 10-2 eV
H ~ m2/Mp
mw Must rethink how the vacuum gravitates in 6D for these scales.
SM interactions do not change at all!
Cosmo 07
The SLED Proposal
• Suppose physics is extra-dimensional above the 10-2 eV scale.
• Suppose the physics of the bulk is supersymmetric.
Aghababaie, CB, Parameswaran & Quevedo
Cosmo 07
The SLED Proposal
• Suppose physics is extra-dimensional above the 10-2 eV scale.
• Suppose the physics of the bulk is supersymmetric.
• 6D gravity scale: Mg ~ 10 TeV
• KK scale: 1/r ~ 10-2 eV
• Planck scale: Mp ~ Mg2 r
Arkani-Hamad, Dimopoulos & Dvali
Cosmo 07
• Suppose physics is extra-dimensional above the 10-2 eV scale.
• Suppose the physics of the bulk is supersymmetric.
The SLED Proposal
• 6D gravity scale: Mg ~ 10 TeV
• KK scale: 1/r ~ 10-2 eV
• Planck scale: Mp ~ Mg2 r
• Choose bulk to be supersymmetric(no 6D CC allowed)
Nishino & Sezgin
Cosmo 07
• Suppose physics is extra-dimensional above the 10-2 eV scale.
• Suppose the physics of the bulk is supersymmetric.
The SLED Proposal
• 6D gravity scale: Mg ~ 10 TeV
• KK scale: 1/r ~ 10-2 eV
• Planck scale: Mp ~ Mg2 r
• SUSY Breaking on brane: TeVin bulk: Mg
2/Mp ~1/r
Cosmo 07
The SLED Proposal
4D graviton
m ~ Mw2/Mp
H ~ m2/Mp
Mw
Particle Spectrum:
4D scalar: e r2 ~ const
SM on brane – no partners
Many KK modes in bulk
Cosmo 07
What Needs Understanding
• Classical part of the argument:• What choices must be
made to ensure 4D flatness?
• Quantum part of the argument:• Are these choices stable
against renormalization?
Cosmo 07
• Classical part of the argument:• What choices must be
made to ensure 4D flatness?
• Quantum part of the argument:• Are these choices stable
against renormalization?
What Needs Understanding
• Search for solutions to 6D supergravity: • What bulk geometry arises from a given
brane configuration?
• What is special about the ones which are 4D flat?
Cosmo 07
• Classical part of the argument:• What choices must be
made to ensure 4D flatness?
• Quantum part of the argument:• Are these choices stable
against renormalization?
What Needs Understanding
• Search for solutions to 6D supergravity: • What bulk geometry arises from a given
brane configuration?
• What is special about the ones which are 4D flat?
• Bulk solutions known for most properties for 2 brane sources;
• Most have runaway behaviour, with extra dimensions growing or collapsing
• Sufficient condition for flatness is absence of brane-dilaton coupling.
Cosmo 07
What Needs Understanding
• Classical part of the argument:• What choices must be
made to ensure 4D flatness?
• Quantum part of the argument:• Are these choices stable
against renormalization?
Cosmo 07
What Needs Understanding
• Classical part of the argument:• What choices must be
made to ensure 4D flatness?
• Quantum part of the argument:• Are these choices stable
against renormalization?
• When both branes have conical singularities all static solutions have 4D minkowski geometry.
• Conical singularities require vanishing dilaton coupling to branes (and hence scale invariant)
Cosmo 07
What Needs Understanding
• Classical part of the argument:• What choices must be
made to ensure 4D flatness?
• Quantum part of the argument:• Are these choices stable
against renormalization?
• When both branes have conical singularities all static solutions have 4D minkowski geometry.
• Conical singularities require vanishing dilaton coupling to branes (and hence scale invariant)
• Brane loops on their own cannot generate dilaton couplings from scratch.
Cosmo 07
What Needs Understanding
• Classical part of the argument:• What choices must be
made to ensure 4D flatness?
• Quantum part of the argument:• Are these choices stable
against renormalization?
• When both branes have conical singularities all static solutions have 4D minkowski geometry.
• Conical singularities require vanishing dilaton coupling to branes (and hence scale invariant)
• Brane loops on their own cannot generate dilaton couplings from scratch.
• Bulk loops can generate brane-dilaton coupling but TeV scale modes are suppressed at one loop by 6D supersymmetry
Cosmo 07
What Needs Understanding
• Classical part of the argument:• What choices must be
made to ensure 4D flatness?
• Quantum part of the argument:• Are these choices stable
against renormalization?
• When both branes have conical singularities all static solutions have 4D minkowski geometry.
• Conical singularities require vanishing dilaton coupling to branes (and hence scale invariant)
• Brane loops on their own cannot generate dilaton couplings from scratch.
• Bulk loops can generate brane-dilaton coupling but TeV scale modes are suppressed at one loop by 6D supersymmetry
• Each bulk loop costs power of e ~ 1/r2 and so only a few loops must be checked…..
Cosmo 07
Observational Consequences
• Quintessence cosmology
• Modifications to gravity
• Collider physics
• Neutrino physics?
• And more!
SUSY broken at
the TeV scale,
but not the MSSM!
Cosmo 07
Summary
• It is too early to abandon naturalness as a fundamental criterion!
• It is the interplay between cosmological phenomenology and microscopic constraints which will make it possible to solve the Dark Energy problem.• Technical naturalness provides a crucial clue.
Cosmo 07
Summary
• It is too early to abandon naturalness as a fundamental criterion!
• It is the interplay between cosmological phenomenology and microscopic constraints which will make it possible to solve the Dark Energy problem.• Technical naturalness provides a crucial clue.
• 6D brane-worlds allow progress on technical naturalness:• Vacuum energy not equivalent to curved 4D
• Are ‘Flat’ choices stable against renormalization?
Cosmo 07
Summary
• It is too early to abandon naturalness as a fundamental criterion!
• It is the interplay between cosmological phenomenology and microscopic constraints which will make it possible to solve the Dark Energy problem.• Technical naturalness provides a crucial clue.
• 6D brane-worlds allow progress on technical naturalness:• Vacuum energy not equivalent to curved 4D
• Are ‘Flat’ choices stable against renormalization?
• Tuned initial conditions• Much like for the Hot Big Bang Model.
Cosmo 07
Summary
• It is too early to abandon naturalness as a fundamental criterion!
• It is the interplay between cosmological phenomenology and microscopic constraints which will make it possible to solve the Dark Energy problem.• Technical naturalness provides a crucial clue.
• 6D brane-worlds allow progress on technical naturalness:• Vacuum energy not equivalent to curved 4D
• Are ‘Flat’ choices stable against renormalization?
• Tuned initial conditions• Much like for the Hot Big Bang Model.
• Enormously predictive, with many observational consequences.• Cosmology at Colliders! Tests of gravity…
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
Inflationary models must be embedded into a fundamental theory in order to explain:
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
Inflationary models must be embedded into a fundamental theory in order to explain:
* Why the inflaton potential has its particular finely-tuned shape
(and if anthropically explained, what assigns the probabilities?)
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
Inflationary models must be embedded into a fundamental theory in order to explain:
* Why the inflaton potential has its particular finely-tuned shape
(and if anthropically explained, what assigns the probabilities?)
* What explains any special choices for initial conditions
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
Inflationary models must be embedded into a fundamental theory in order to explain:
* Why the inflaton potential has its particular finely-tuned shape
(and if anthropically explained, what assigns the probabilities?)
* What explains any special choices for initial conditions
* Why the observed particles get heated once inflation ends.
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
Inflationary models must be embedded into a fundamental theory in order to explain:
* Why the inflaton potential has its particular finely-tuned shape
(and if anthropically explained, what assigns the probabilities?)
* What explains any special choices for initial conditions
* Why the observed particles get heated once inflation ends.
Can identify how robust inflationary predictions are to high-energy details, and so also what kinds of very high-energy physics might be detectable using CMB measurements.
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
String theory has many scalars having very flat potentials.
These scalars (called moduli) describe the shape and size of the various extra dimensions
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
String theory has many scalars having very flat potentials.
BUT their potentials are usually very difficult to calculate.
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
String theory has many scalars having very flat potentials.
BUT their potentials are usually very difficult to calculate.
A convincing case for inflation requires knowing the potential for all of the scalars.
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
String theory has many scalars having very flat potentials.
BUT their potentials are usually very difficult to calculate.
A convincing case for inflation requires knowing the potential for all of the scalars.
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
For Type IIB strings it is now known how to compute the potentials for some of the low-energy string scalars.
GKP
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
Branes want to squeeze extra dimensions while the fluxes they source want the extra dimensions to grow. The competition stabilizes many of the ‘moduli’
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned? The moduli which remain after
this stabilization can also acquire a potential due to nonperturbative effects. Plausibly estimated…KKLT models
KKLT, KKLMMT
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned? The moduli which remain after
this stabilization can also acquire a potential due to nonperturbative effects. Improved for P4[11169]
‘The Better Racetrack’Douglas & Denef
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned? The inflaton in these models can
describe the relative positions of branes; or the volume or shape of the extra dimensions.
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
The motion of several complex fields must generically be followed through a complicated landscape: many possible trajectories for each vacuum
Cosmo 07
String Inflation
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned? The potential can inflate, e.g. for
some choices for the properties of P4[11169] – giving rise to realistic inflationary fluctuations
The ‘Racetrack Eight’
Cosmo 07
String Inflation
CMB measurements begin to distinguish different inflationary models
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
Barger et al hep-ph/0302150
- model comparisons
Cosmo 07
String Inflation
CMB measurements begin to distinguish different inflationary models
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
WMAP preferred
- model comparisons
Cosmo 07
String Inflation
Trajectories through string landscape predict same regions as do their low-energy effective theories.
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
brane-antibrane
racetrack
- model comparisons
Cosmo 07
String Inflation
The measurements can already distinguish amongst some stringy inflationary models.
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
KKLMMT*
P4[11169]
WMAP preferred
- model comparisons
KKLMMT, BCSQ, Racetrack 8
Cosmo 07
String Inflation
Most inflationary trajectories require fine tuning as do their field theory counterparts…
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
- model comparisons
- naturalness
KKLMMT, BCSQ, Racetrack 8
Cosmo 07
String Inflation
Two possible exceptions:
DBI Inflation: relativistic brane motion where H changes slowly.
Kahler moduli inflation: slow roll from ‘generic’ approximations.
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
- model comparisons
- naturalness
Silverstein & TongBCSQ, Conlon & Quevedo
nn MbMBAV )/(exp)/(
srM M 1,
Cosmo 07
String Inflation
Although robust against most stringy details, predictions for CMB can be sensitive to specific kinds of physics near horizon exit
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
H-1(t) (t)
Inflation Post-Inflation
Length
Time
p
oscillations 60 e-foldings
10-30 e-foldings
- model comparisons
- naturalness
- robustness
Cosmo 07
String Inflation
Although robust against most stringy details, predictions for CMB can be sensitive to specific kinds of physics near horizon exit
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
- model comparisons
- naturalness
- robustness
Cosmo 07
String Inflation
Although robust against most stringy details, predictions for CMB can be sensitive to specific kinds of physics near horizon exit
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
- model comparisons
- naturalness
- robustness
Cosmo 07
String Inflation
Although robust against most stringy details, predictions for CMB can be sensitive to specific kinds of physics near horizon exit
• Why try to embed inflation into string theory?
• Why is it hard?
• What have we learned?
- model comparisons
- naturalness
- robustness
Cosmo 07
Outlook
• Branes continue to provide a useful approach for naturalness problems.• Dark Energy, Hierarchy Problem, Inflation… more?
• We are very close to finding inflation in explicit controlled string calculations• Possible progress on fine-tunings;
• New insights on reheating (eg cosmic strings);
• Signals largely robust, except near horizon exit
• Small tensor perturbations?
• Possibly even more novel physics can arise!