String Inflation
Is it helping?
C.P. Burgess
Outline
• Helping with what?
• Why build models only a mother could love?
• What might help look like?
•
•
•
•
Mechanisms; robustness
Initial conditions; naturalness;
Reheating and scales; signatures;
Mind-broadening;…
• A tentative scorecard
UniverseNet Lecce 2010
Outline
• Helping with what?
• Why build models only a mother could love?
• What might help look like?
•
•
•
•
Mechanisms; robustness
Initial conditions; naturalness;
Reheating and scales; signatures;
Mind-broadening;…
• A tentative scorecard
UniverseNet Lecce 2010
Outline
• Helping with what?
• Why build models only a mother could love?
• What might help look like?
•
•
•
•
Mechanisms; robustness
Initial conditions; naturalness;
Reheating and scales; signatures;
Mind-broadening;…
• A tentative scorecard
UniverseNet Lecce 2010
Help with what?
• What needs fixing?
• about inflation
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
• What needs fixing?
• about inflation
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
Observation:
• What needs
fixing? horizon and flatness problems (and
possibly defect problem) arise because the co• about inflation
-1/a = (1/aH), grows
moving
Hubble
length,
H
• about strings
during the present Hot Big Bang epoch.
• What might
Length one hope to H (t)
learn?
-1
a  t1/ 2 ; H 1  t
• about inflation
• about strings
(t)
• Why now?
Time
UniverseNet Lecce 2010
Help with what?
Starobinsky; Guth
Linde; Albrecht & Steinhardt
Theyfixing?
would be resolved if H-1/a = (1/aH), were
• What needs
instead to shrink during an earlier epoch.
• about inflation
• about strings
e.g. exponential inflation: a = a0 eHt
• What might
Length one hope to H (t)
learn?
-1
• about inflation
Inflation
• about strings
(t)
(t)
• Why now?
Post-Inflation
a  t1/ 2 ; H 1  t
a  e Ht ; H 1  const.
60 e-foldings
Time
UniverseNet Lecce 2010
Help with what?
Mukhanov, Linde, Hawking, Steinhardt, Guth, Pi,…
• What needs fixing?
• about inflation
• about strings
• What might one hope to
learn?
• about inflation
• about strings
Inflationary Bonus: Simple models provide a good
• Why now?
description of primordial fluctuations.
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
1 2
• What might one hope toL  2   V  
learn?
M p2 V  2m 2


 1
• about inflation
2
V
3
H
• about strings
• Why now?
2
2
g
M
 m2 
16 2
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
*




• What might one hope
to
V  V0 1  2  
 M

learn?
p


• about inflation
• about strings
• Why now?
  1
‘Planck slop’
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings

Tuning: technical naturalnessor control
 * of approximations?
 V0 1  2  
• What might one hopeV to
 M

p


learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings

Technically unnatural: eg theelectroweak
hierarchy
 *
 V0 1  2  
• What might one hopeV to
 M

p
M ~10 GeV


learn?
p
18
• about inflation
M ~ 10strings
GeV
• about
11
Mw102 GeV
• Why now?
m  m 
2
2
0
Leff  m02 H *H  ...
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings

Technically unnatural: eg theelectroweak
hierarchy
 *
 V0 1  2  
• What might one hopeV to
 M

p
M ~10 GeV


learn?
p
18
• about inflation 2
2
2
m

m

k
M

1
M ~ 10strings
GeV
• about
11
Mw102 GeV
• Why now?
m  m 
2
2
0
Leff  m12 H *H  ...
Leff  m02 H *H  ...
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings

Technically unnatural: eg theelectroweak
hierarchy
 *
 V0 1  2  
• What might one hopeV to
 M

p
M ~10 GeV


learn?
p
18
• about inflation 2
2
2
m

m

k
M

1
M ~ 10strings
GeV
• about
11
Mw102 GeV
• Why now?
m  m 
2
2
0
Must cancel to 20
decimal places!!
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
Technically natural: eg size of atoms
 *vs size of nuclei
 V0 1  2  
• What might one hopeV to
 M

p
 me   QCD

learn?
M ~ QCD
• about inflation
• about strings
Mme
• Why now?
 me  m p
UniverseNet Lecce 2010
Help with what?
‘t Hooft
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
Technically natural: eg size of atoms
 *vs size of nuclei
 V0 1  2  
• What might one hopeV to
 M

p
 me   QCD

learn?
M~ 
QCD
• about inflation
M~m
• about strings

Mme
• Why now?
 me  m p
    m 
 me    log  
 4   me 
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
*
depends on the
Whether inflationary models are unnatural


  2  
V to
 Vvery
0  1 high
• What
mightcontent
one hope
particle
at these

M energies.

learn?
p

2
2
g
M
2
• about inflation  m 

H
?
2
16
• about strings
2
String inflationary models tend to be natural in this sense
• Why
now? of supersymmetry, shift symmetry, extra dims
because
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
*
 sounnatural,
 technically.
Tunings to 1 part in 100 are not

 V0 1  2  
• What might one hopeV to
 M

p
learn?
   *
 
• about inflation
• about strings
• Why now?
V  V0 1  c 2  


M
p


  0.01

c  0.01
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
*
 ofapproximations:

Tuning: the real issue is control

V to
 V0 1  2  
• What
might
one
hope
 to inflate
 a given set
if a given potential is asserted
within
M
p


learn?
of approximations, have all contributions been included
• about
to theinflation
required accuracy?
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
Copeland et al,
Kachru, McAllister,….
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
*
 ofapproximations:

Tuning: the real issue is control

V to
 V0 1  2  
• What
might
one
hope
 to inflate
 a given set
if a given potential is asserted
within
M
p


learn?
of approximations, have all contributions been included
• about
to theinflation
required accuracy?
• about strings
*





V  V0 1  c 2  


e.g. Planck slop:
Mp
• Why now?


UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
Are predictions
of simple models robust?
• What might
one hope to
learn?

2
i
j
e.g.   V    Gij     V 
• about inflation

• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
Are predictions
of simple models robust?
• What might
one hope to
learn?
Sometimes special initial conditions required
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
But….
• What needs
fixing?
• about inflation
Simple inflation models require tuned potentials
• about strings
Are predictions
of simple models robust?
• What might
one hope to
learn?
Sometimes special initial conditions required
• about inflation
• about strings
How does reheating work, and what are the degrees
of freedom that are relevant?
• Why now?
UniverseNet Lecce 2010
Help with what?
• What needs
fixing?
String
Theory:
• about inflation
• about strings
Best explored, and
possibly the only,
quantum
theoryto
of gravity
• What might
one hope
learn? at small distances
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
• What needs
fixing?
String
Theory:
• about inflation
• about strings
Best explored, and
possibly the only,
quantum
theoryto
of gravity
• What might
one hope
learn? at small distances
• about inflation
First known theory that
• about strings
could be the theory of
everything
• Why now?
UniverseNet Lecce 2010
Help with what?
• What needs
fixing?
But….
• about inflation
• about strings
How to make contact with
experiment given that Ms
is likely
• What might
one very
hopelarge?
to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
• What needs
fixing?
But….
• about inflation
• about strings
How to make contact with
experiment given that Ms
is likely
• What might
one very
hopelarge?
to
learn?
How does one make
• about inflation
falsifiable predictions
• about strings
with enormous number
of vacua?
• Why now?
UniverseNet Lecce 2010
Help with what?
• What needs
fixing?
Inflation:
impressive phenomenology seeking a
fundamental theory within which to sit;
• about inflation
• about strings
String Theory: an impressive fundamental theory
seeking
• What might
oneexperimental
hope to consequences to test
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
courtesy of Rocky Kolb
• What needs fixing?
• about inflation
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
• What needs fixing?
• about inflation
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What we’d
like string theory to tell us about inflation:
• What needs
fixing?
How generic is it in the landscape?
• about inflation
Initial conditions, flat potentials, …
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What we’d
like string theory to tell us about inflation:
• What needs
fixing?
How generic is it in the landscape?
• about strings
Initial conditions, flat potentials, …
• about inflation
How does reheating work?
Does SM couple strongly enough to inflaton?
• What might one hope to
Do other channels couple even more strongly?
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What we’d
like string theory to tell us about inflation:
• What needs
fixing?
How generic is it in the landscape?
• about strings
Initial conditions, flat potentials, …
• about inflation
How does reheating work?
Does SM couple strongly enough to inflaton?
• What might one hope to
Do other channels couple even more strongly?
learn?
What are the other dimensions doing?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What we’d
like string theory to tell us about inflation:
• What needs
fixing?
How generic is it in the landscape?
• about strings
Initial conditions, flat potentials, …
• about inflation
How does reheating work?
Does SM couple strongly enough to inflaton?
• What might one hope to
Do other channels couple even more strongly?
learn?
What are the other dimensions doing?
• about inflation
How robust are inflationary inferences drawn
• about strings
using simple single-field slow-roll models?
• Why now?
UniverseNet Lecce 2010
Help with what?
What we’d
like string theory to tell us about inflation:
• What needs
fixing?
How generic is it in the landscape?
• about strings
Initial conditions, flat potentials, …
• about inflation
How does reheating work?
Does SM couple strongly enough to inflaton?
• What might one hope to
Do other channels couple even more strongly?
learn?
What are the other dimensions doing?
• about inflation
How robust are inflationary inferences drawn
• about strings
using simple single-field slow-roll models?
• Why now?Are qualitatively new kinds of signatures or
mechanisms possible?
UniverseNet Lecce 2010
Help with what?
• What needs fixing?
• about inflation
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What we’d
like inflation to tell us about string theory:
• What needs
fixing?
• about strings
• aboutPredicting
inflation in the landscape: perhaps some features of
present-day universe correlate with its earlier history
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What we’d
like inflation to tell us about string theory:
• What needs
fixing?
• about strings
• aboutPredicting
inflation in the landscape: perhaps some features of
present-day universe correlate with its earlier history.
• What might one hope to
learn? Inflationary mechanisms can be among other lowenergy modules that guide the search for realistic
• about inflation
vacua among the many string solutions.
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What we’d
like inflation to tell us about string theory:
• What needs
fixing?
• about strings
• aboutPredicting
inflation in the landscape: perhaps some features of
present-day universe correlate with its earlier history.
• What might one hope to
learn? Inflationary mechanisms can be among other lowenergy modules that guide the search for realistic
• about inflation
vacua among the many string solutions.
• about strings
Can hope to learn about time-dependent solutions and
• Why now?non-supersymmetric parts of the landscape.
UniverseNet Lecce 2010
Help with what?
• What needs fixing?
• about inflation
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What isfixing?
so hard about finding inflation in string theory?
• What needs
• about inflation
has many 4D scalars. (brane positions; or moduli)
• aboutItstrings
gmn x   gmn  ; x 
i
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
What isfixing?
so hard about finding inflation in string theory?
• What needs
• about inflation
has many 4D scalars; supersymmetry can give these
• aboutItstrings
very flat potentials
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
Brustein & Steinhardt
What isfixing?
so hard about finding inflation in string theory?
• What needs
• about inflation
has many 4D scalars; supersymmetry can give these
• aboutItstrings
very flat potentials;
BUT: a convincing case for inflation requires reliably
• What might one hope to
knowing the potential that stabilizes moduli
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
Giddings, Kachru & Polchinski
Kachru, Kallosh, Linde & Trivedi
It has recently
• What needs
fixing? become possible to compute the lowenergy potential for all moduli for some string
• about inflation
constructions
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
Giddings, Kachru & Polchinski
Kachru, Kallosh, Linde & Trivedi
It has recently
• What needs
fixing? become possible to compute the lowenergy potential for all moduli for some string
• about inflation
constructions: First done for Type IIB vacua
• about strings
Key ingredients:
• What might
one hope to
learn? D3 and D7 branes &
• aboutorientifolds
inflation
• aboutFluxes
stringssourced by these
branes, wrapping extra
dimensions
• Why now?
UniverseNet Lecce 2010
Help with what?
Giddings, Kachru & Polchinski
It has recently
• What needs
fixing? become possible to compute the lowenergy potential for all moduli for some string
• about inflation
constructions: First done for Type IIB vacua
• about strings
At low energies: a 4D noscale sugra:
• What might
one hope to
learn? K  2 ln V  2 ln t13 / 2  t 23 / 2 
• about inflation
W  W0
• about strings
• Why now?
for moduli Ti=ti + i bi
UniverseNet Lecce 2010
Help with what?
Klebanov & Strassler
• What needs

2
1 / 2
m
n
1/ 2
2
2
2
ds

h

dx
dx

h
dr

r
d

mn
fixing?
• about inflation
• about strings

h  1/ r4
dr 2
ds  r mndx dx  2  d2
r
2
2
m
n
Strongly warped throats
• What might
hopetotospecific
arise inone
response
learn? flux configurations.
• about inflation
• aboutWarped
strings throats strongly
redshift energies à la
• Why now?
Randall & Sundrum
UniverseNet Lecce 2010
Help with what?
Kachru, Kallosh, Linde & Trivedi
Denef & Douglas
Use other
means (wrapped ED3, gaugino
• What needs
fixing?
condensation) to stabilize remaining moduli
• about inflation
• about strings
KKLT regime
• What might
K  2one
ln V hope
2 ln to
t13 / 2  t 23 / 2 
learn?
a1T1
a2T2
W

W

A
e

A
e
• about inflation
0
1
2
• aboutbelieve
stringsapproximations if
W0  A e
• Why now?
aT
 1
UniverseNet Lecce 2010
Help with what?
Balasubramanian, Bergland,
Conlon, Quevedo
Use other
means (wrapped ED3, gaugino
• What needs
fixing?
condensation) to stabilize remaining moduli
• about inflation
• about strings
Large-volume regime:
a to
• What might
one
hope
K  2 ln V   Kloop
V
learn?
a1T1
a2T2
W

W

A
e

A
e
• about inflation
0
1
2
• aboutfor
strings
W0 ~ O(1) can believe
approximations if
• Why now?V  eaT
2
t 2  c / gs
UniverseNet Lecce 2010
Help with what?
KKLT
In bothfixing?
cases minimum is at negative potential.
• What needs
SUSY is unbroken at this minimum for KKLT
• about inflation
but is spontaneously broken there for LV models.
• about strings
• What might one hope to
learn?
• about inflation
• about strings
• Why now?
UniverseNet Lecce 2010
Help with what?
KKLT
CB, Kallosh & Quevedo
In bothfixing?
cases minimum is at negative potential.
• What needs
SUSY is unbroken at this minimum for KKLT
• about inflation
but is spontaneously broken there for LV models.
• about strings
Uplift to zero/positive using:
antibrane
throatto
• What might
oneinhope
learn? (explicit SUSY breaking);
• aboutorinflation
• aboutmagnetized
strings branes
E
(if possible)
U  p
• Why now?
V
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Dvali and Tye
BMNQRZ
KKLMMT
Silverstein & Tong
Several candidates for the inflaton: Most explicitly
Mechanisms
embedded into string theory are open string modes:
Robustness
D3 brane motion along a warped throat
Initiale.g.
Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Baumann et al
•
•
•
•
•
•
•
Several candidates for the inflaton: Most explicitly
Mechanisms
embedded into string theory are open string modes:
Robustness
developed to date: D3 moving in throat under
InitialBest
Conditions
influence of forces due to D7s
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
Emerging Picture
•
•
•
•
•
•
•
CB, Quevedo, Rajesh & Zhang
Blanco-Pillado et al
Conlon & Quevedo
Bond, Kofman & Prokushkin
Kahler moduli can also be candidate inflatons
Mechanisms
Closed string modes: eg
Robustness
volume and shape of extra
Initialdimensions,
Conditions
or their
superpartner axions
Naturalness
Reheating
& scales
eg: Better
Racetrack:
K  2 ln V  2 ln t13 / 2  t 23 / 2 
Signatures
W  W0  A1ea T  A2ea T
Mind broadening
1 1
2 2
in KKLT regime
UniverseNet Lecce 2010
Emerging Picture
•
•
•
•
•
•
•
CB, Quevedo, Rajesh & Zhang
Blanco-Pillado et al
Conlon & Quevedo
Bond, Kofman & Prokushkin
Kahler moduli can also be candidate inflatons
Mechanisms
Closed string modes: eg
Robustness
volume and shape of extra
Initialdimensions,
Conditions
or their
superpartner axions
Naturalness
Reheating
& scales
Less well
developed so far
inasmuch as inflationary
Signatures
tunings are not known to be
Mind achievable
broadening
from explicit
underlying string vacua
UniverseNet Lecce 2010
Emerging Picture
•
•
•
•
•
•
•
All models so far compute the inflationary response to
Mechanisms
the assumed dynamics within the 4D effective field
theory.
Robustness
Initial Conditions H  M
kk
Naturalness
What are
the other dimensions doing?
Reheating
& scales
Signatures
Do we only find 4D effects because we exclusively
Mind broadening
look under a 4D lamppost?
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Inflation generically involves several light fields
Mechanisms
moving in a relatively complicated potential
Robustness
Many more heavy fields exist
Initial Conditions
Naturalness
Do these
Reheating
& destroy
scalesthe
successful inflationary
Signatures
phenomenology?
Mind broadening
Brandenberger et al and many more…
UniverseNet Lecce 2010
What might help look like?
Blanco-Pillado et al
Postma et al
•
•
•
•
•
•
•
Single-field slow-roll analyses capture much of the
Mechanisms
generic predictions for the CMB
Robustness
InitialBut
Conditions
must check: The
presence of multiple
Naturalness
scalars allows in
principle
Reheating
& observable
scales
new features like
Signatures
isocurvature
Mind perturbations,
broadening
nongaussianity, etc
UniverseNet Lecce 2010
What might help look like?
Kaloper, Kleban, Lawrence & Shenker
CB, Cline, Holman & Lemieux
•
•
•
•
•
•
•
Heavier fields tend to decouple from inflationary
Mechanisms
predictions, with contributions of order H2/M2
Robustness
InitialTwo
Conditions
kinds of effects can
be larger than the naïve
Naturalness
H2/M2 suppression:
Reheating
& scales
Non-adiabatic
effects
near horizon exit;
Signatures
or
Mind broadening
2
2
2
 /M where H =  /Mp
H-1(t)
Length
10-30 e-foldings
Inflation
(t)
Post-Inflation
oscillations
60 e-foldings
p
Time
UniverseNet Lecce 2010
What might help look like?
CB, Cline, Holman & Lemieux
•
•
•
•
•
•
•
Heavier fields tend to decouple from inflationary
Mechanisms
predictions, with contributions of order H2/M2
Robustness
InitialTwo
Conditions
kinds of effects can
be larger than the naïve
Naturalness
H2/M2 suppression:
Reheating
& scales
Non-adiabatic
effects
near horizon exit;
Signatures
or
Mind broadening
2
2
2
 /M where H =  /Mp
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Inflation can depend sensitively on inflaton’s initial
Mechanisms
conditions
Robustness
eg: Hybrid inflation
Initial Conditions
mechanisms
Naturalness
No new
Reheating
&insights
scales
yet into initial
Signatures
condition problem:
Mind broadening
eternal inflation?
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Slow rolls appear not to be generic.
Mechanisms
Robustness
Usually requires tuning parameters in the potential. (for
IIB models at least allow lots of values.)
Initialwhich
Conditions
Naturalness
But the basic hierarchy
problem
(large
Reheating
& scales
contributions to masses)
Signatures
is usually addressed by
mechanism like susy or
Mind broadening
shift symmetry
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
String inflation models are baroque in order to keep
Mechanisms
control over all approximations being used.
Some generic weaknesses to models:
Robustness
Initial Conditions
Need for uplifting and control over calculations in
Naturalness
presence of anti-branes
Reheating & scales
Inflation seekers scan through parameters of 4D action
Signatures
as if these are free and not calculable.
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Freese, Frieman & Olinto; Kachru et al
McAllister, Silverstein & Westphal
•
•
•
•
•
•
•
Two possible more natural mechanisms:
Mechanisms
Inflaton as a pseudo Goldstone boson (axion)
Robustness
Veff  A  B  C cos / f 
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
CB, Martineau, Quevedo, Rajesh & Zhang
•
•
•
•
•
•
•
Two possible more natural mechanisms:
Mechanisms
Large field models where inflaton is modulus
Robustness
2
Initial Conditions

r  
B
Leff   2   A  n 
r
r 

Naturalness
2
Reheating & scales


Leff     A  B e / M 
Signatures
since regime where r > ls corresponds to  > M,
Mind broadening
which is a slow roll regime (and large  makes
Planck-slop objection more subtle)
UniverseNet Lecce 2010
What might help look like?
Conlon & Quevedo
Cicoli, CB & Quevedo
•
•
•
•
•
•
•
Possible large-volume realizations:
Mechanisms
Kahler modulus inflation: (t1 >> t2 ~ t3)
Robustness
K  2 ln t 13 / 2  t 23 / 2  t 33 / 2    
Initial Conditions
W  W0  A1ea T  A2ea T  A3ea T
Naturalness Ueff  A  B( / M )n exp  bV a ( / M )n 
Reheating
scales(t1 >> t2 >> t3)
Fibre&
inflation:
SignaturesK  2 ln t11/ 2 t 2  bt1   t 33/ 2    Kloop
Mind broadening
U eff  A  B exp   / M 
1 1
2 2
3 3
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Questions:
Mechanisms
Are all contributions to U known at the required size?
Robustness
Initial Conditions
What is the upper limit to the range allowed for ?
Naturalness
Reheating & scales
For models based on large volume, how does one
Signatures
ensure observably large fluctuations?
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Proper reheating story awaits locating ordinary particles
Mechanisms
somewhere in the inflationary geometry
Robustness
Plausibly (but not necessarily) located on a brane in
warped throat
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
CB, Majumdar, Nolte, Quevedo, Rajesh & Zhang
Karsh & Randall
•
•
•
•
•
•
•
Brane annihilation provides a novel energy release
Mechanisms
including cascade to branes of lower dimension
Robustness
(mechanism for preferring low-dimension branes at
late times like D3s and cosmic strings?)
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Barnaby et al
Kofman & Yi
Chialva, Shiu & Underwood
Langfelder
•
•
•
•
•
•
•
If so, must understand why energy does not prefer to
Mechanisms
go into bulk modes rather than observable ones.
Robustness
Warped reheating: warping may provide a relatively
efficient cascade of energy into the lowest throat.
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Kallosh & Linde
CB, Quevedo, Rajesh & Zhang
•
•
•
•
•
•
•
The problem of scales:
Mechanisms
Robustness
In the available models the string scale, Ms, required
to obtain the right amplitude for primordial scalar
Initial perturbations
Conditionsgives a supersymmetry breaking scale
which is too high to solve the hierarchy problem.
Naturalness
Reheating & scales
eg: for warped models: cannot make 2nd throat too
Signatures
deep if inflation occurs in 1st throat
or: for large-volume models:
Mind broadening
Ms ~ Mp/V1/2;
m3/2 ~ Mp/V ~ Ms/V1/2
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Possible ways out:
Mechanisms
Robustness
Low-scale inflation (German, Ross & Sarkar)
Initial Conditions
Generate inflationary perturbations through other
Naturalness
means
Reheating & scales
Allow Ms to roll to larger values after inflation
Signatures
(Conlon, Kallosh, Linde & Quevedo)
Mind broadening
4D calculation possible in CFT dual to warped throat.
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Sarangi & Tye
Jones, Stoica & Tye
Copeland, Myers & Polchinski
•
•
•
•
•
•
•
Brane annihilation can lead to interesting abundances
Mechanisms
of cosmic strings with interesting properties.
Robustness
nonstandard reconnections; G2 ~ 10-8-10-12
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Because inflation is found in 4D effective theory,
Mechanisms
predictions tend to be contained within those of the
corresponding 4D mechanism
Robustness
InitialSmall-field
Conditions
models
Large-field models
Naturalness
Hybrid&
models
Reheating
scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Kallosh & Linde
Baumann & McAllister
•
•
•
•
•
•
•
Because inflation is found in 4D effective theory,
Mechanisms
predictions tend to be contained within those of the
corresponding 4D mechanism
Robustness
InitialSmall-field
Conditions
models
Large-field models
Naturalness
Hybrid&
models
Reheating
scales
Signatures
Apparently general
prediction?
Mind stringy
broadening
small tensor amplitude
UniverseNet Lecce 2010
What might help look like?
Silverstein & Westphal
McAllister, Silverstein & Westphal
CB, Cicoli & Quevedo
•
•
•
•
•
•
•
Because inflation is found in 4D effective theory,
Mechanisms
predictions tend to be contained within those of the
corresponding 4D mechanism
Robustness
InitialSmall-field
Conditions
models
Large-field models
Naturalness
Hybrid&
models
Reheating
scales
Signatures
Apparently general
prediction?
Mind stringy
broadening
small tensor amplitude
UniverseNet Lecce 2010
What might help look like?
Maldacena & Nunez;
Gibbons; Kachru & Taylor; Wesley
•
•
•
•
•
•
•
Explicit inflationary solutions to higher dimensional
Mechanisms
field equations are difficult to achieve: is this in itself
an example of string theory producing only a subset of
Robustness
what could be found in the swampland?
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Covi, Gomez-Reino, Gross,
Louis, Palma & Srucca
•
•
•
•
•
•
•
Explicit inflationary solutions to higher dimensional
Mechanisms
field equations are difficult to achieve: is this in itself
an example of string theory producing only a subset of
Robustness
what could be found in the swampland?
Initial Conditions
Naturalness
Inflationary classical solutions to 4D supergravity
equations are also difficult to achieve
Reheating & scales
2
2
m
Signatures R f i f j f m f n 
3l 2
ijmn
2
2
3
(
m

H
)
3/ 2
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Several novel features and mechanisms have emerged
Mechanisms
Brane-antibrane annihilation, and the absence of the
Robustness
inflaton in the post-inflationary low-energy theory;
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Myers, Frey & Mazumdar
Buchel & Kofman
•
•
•
•
•
•
•
Several novel features and mechanisms have emerged
Mechanisms
Brane-antibrane annihilation, and the absence of the
Robustness
inflaton in the post-inflationary low-energy theory;
Initial Conditions
AdS/CFT connection: eg: energy dumped into throat
Naturalness
can form evaporating BH there.
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Myers, Frey & Mazumdar
Buchel & Kofman
•
•
•
•
•
•
•
Several novel features and mechanisms have emerged
Mechanisms
Brane-antibrane annihilation, and the absence of the
Robustness
inflaton in the post-inflationary low-energy theory;
Initial Conditions
AdS/CFT connection: eg: energy dumped into throat
Naturalness
can form evaporating BH there.
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Myers, Frey & Mazumdar
Buchel & Kofman
•
•
•
•
•
•
•
Several novel features and mechanisms have emerged
Mechanisms
Brane-antibrane annihilation, and the absence of the
Robustness
inflaton in the post-inflationary low-energy theory;
Initial Conditions
AdS/CFT connection: eg: energy dumped into throat
Naturalness
can form evaporating BH there.
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Silverstein & Tong
•
•
•
•
•
•
•
Several novel features and mechanisms have emerged
Mechanisms
Brane-antibrane annihilation, and the absence of the
Robustness
inflaton in the post-inflationary low-energy theory;
Initial Conditions
AdS/CFT connection: eg: energy dumped into throat
Naturalness
can form evaporating BH there.
Reheating & scales
Signatures
Inflation from relativistic motion (DBI inflation)?
Mind broadening
UniverseNet Lecce 2010
What might help look like?
Veneziano et al
Khoury, Ovrut, Steinhardt & Turok
•
•
•
•
•
•
•
Other ways our minds may yet broaden:
Mechanisms
Are there stringy alternatives to inflation?
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
Outline
• Helping with what?
• Why build models only a mother could love?
• What might help look like?
•
•
•
•
Mechanisms; robustness
Initial conditions; naturalness;
Reheating and scales; signatures;
Mind-broadening;…
• A tentative scorecard
UniverseNet Lecce 2010
What might help look like?
•
•
•
•
•
•
•
Mechanisms
Robustness
Initial Conditions
Naturalness
Reheating & scales
Signatures
Mind broadening
UniverseNet Lecce 2010
Outlook
• There are plausible formulations of inflation in string
theory, but still at the stage of mapping out what is
possible
•
•
•
•
•
Not easy to obtain and keep control over approximations
Possible progress on fine-tunings, but not generically
New insights on reheating (warping, cosmic strings);
Inflationary signals largely robust, except near horizon exit
Examples exist with tensor perturbations, nongaussianity
• Hopefully even more novel physics will emerge…
UniverseNet Lecce 2010
fin
UniverseNet Lecce 2010