Inflation & Cosmology I - A Historical Perspective on Particle Cosmology - SI 2019 - CERN Indico

SI 2019
 20 August, 2019

 Inflation & Cosmology I
- A Historical Perspective on Particle Cosmology -

 Misao Sasaki

 Kavli IPMU, University of Tokyo
 YITP, Kyoto University
 LeCosPA, National Taiwan University

Progress in Particle Cosmology (1)
 1st stage: 1945 ~ 1975
  a  8 G
 2
• 1916~ GR/Friedmann-Lemaitre model K
 H2      2
• 1929 Hubble’s law: V=H0 R a 3 a

• 1946~ Big-Bang theory/Nuclear astrophysics
• 1960~ High redshift objects/Quasars
• 1965 Discovery of relic radiation from Big-Bang
 Cosmic Microwave Background (CMB) ~ 3K
• 1966 Sakharov’s condition
 (but didn’t attract much attention)
 matter-
• 1970~ Big-Bang Nucleosynthesis vs Observed Abundance
 antimatter
 → Existence of Dark Matter (DM) asymmetry
 2

Big Bang Nucleosynthesis (BBN)
George Gamov: pioneer in particle cosmology (1940’s)

 discovery of neutron
 by Chadwick 1932

 • 1st application of nuclear physics
 to cosmology

 • explain light element
 abundance in the Universe

 3

Chushiro Hayashi: father of astro-particle physics in Japan

 • abg incorrectly assumed
 the Universe was totally
 filled by neutrons.
 • Hayashi realized that the
 weak interaction must be
 in thermal equilibrium.
 (1950)
 correct initial cond. for BBN
 nN  m  mP 
  exp   N 
 nP  T 
 m N  mP  1.293 MeV

 nN
  0.2 at T  1010 K
 nP 4

discovery of CMB (1964) = victory of Bing Bang Theory

 Experiment
 • 60’s ~70’s : golden age of particle physics
 • dawn of high energy physics: E GeV
 • accelerator experiments > cosmic ray observations
 CERN, Fermilab, DESI, SLAC, KEK, …
 neutral current 1973, J/y 1974, …
 Theory Nambu ’60
 Goldstone ‘61
 “Spontaneous Symmetry Breakdown”
 • success of Gauge Unification: Weinberg-Salam (1967)
 Standard (Glasho-Weinberg-Salam) Model Strong+Weak+EM
 SU (3)  SU (2) U (1)
 • but no much was done in particle cosmology except for BBN
 computations… 5

Progress in Particle Cosmology (2)
 motivation/
 2nd stage: 1975 ~ 1995 driving force
• 1975 Sato-Sato: Cosmological Constraints on Higgs
• 1977 Sato-Kobayashi: Constraints on Neutrino Mass & Species
• 1977 Yoshimura: Baryogenesis in Grand Unified Theory (GUT)
 Brout, Englert & Gunzig ’77, Starobinsky ’79, Guth ’81,
 Sato ’81, Linde ’81, …
 Dawn of Particle Cosmology/Inflationary Universe
• 1980~ Large Scale Structure : Cold DM (CDM)
 Slow-roll Inflation / Cosmological Perturbation Theory
• 1992 CMB anisotropy by COBE: 1st Evidence for Inflation
 hundreds of models of inflation
 6

Katsuhiko Sato: a great mind of our time
 pioneer of modern particle cosmology

 7

What is Inflation?
 Brout, Englert & Gunzig ’77, Starobinsky ’79, Guth ’81, Sato ’81, Linde ’81,…

 Inflation is a quasi-exponential expansion of the Universe at its
 very early stage; perhaps at t~10-36 sec.
 It is the origin of Hot Bing-Bang Universe
 It was meant to solve the initial condition (singularity, horizon &
 flatness, etc.) problems in Big-Bang Cosmology:
 if any of them can be said to be solved depends on precise
 definitions of the problems.
 Quantum vacuum fluctuations during inflation turn out to play
 the most important role. They give the initial condition for all
 the structures in the Universe.

 Cosmic gravitational wave background is also generated.
 8

Length Scales of Inflationary Universe
 log L End of Inflation
L=H0-1
 superhorizon scales
 k2
 1
 H a
 2 2

 Size of the
 observable
 L=H-1 universe

 k2
 subhorizon scales 1
 H a
 2 2

 log a(t)
 Inflationary Universe Bigbang Universe
 9

Pioneers of Inflation
 Brout, Englert & Gunzig ’77

 温故知新
(learning from the past)

 ds 2  dt 2  a 2 (t )dH(23) ;
 a(t ) H 1 sinh Ht

 Creation of
 Open Universe!
 Now in the context of
String Theory Landscape
 10

Pioneers of Inflation 2
 Starobinsky ‘79 ~ ‘80

 tensor perturbation spectrum
 from de Sitter space

 H
 s
 M pl

 2
  H  GW
PT (k )  
  M pl  rad

 11

Old Inflation
inflation as a 1st order phase transition
 Sato ’81, Guth ’81

 !!

 multiverse!
 12

New (slow-roll) Inflation
+ almost scale-invariant spectrum from vacuum fluctuations
 Linde ’81, Mukhanov & Chibisov ’81

 slow-roll EoM

 13

Slow-roll Inflation
 Linde (1981),…
Universe dominated by a scalar (inflaton) field
For sufficiently flat potential: V()

 8 G  1 2 
 H2  V ( )   2 V ( ) 
 3  
 H 3 2
   1 
 H2 2V ( )
 • H is almost constant ~ exponential expansion = inflation
 •  slowly rolls down the potential: slow-roll (chaotic) inflation
 • Inflation ends when  starts damped oscillation.
  decays into thermal energy (radiation)
 Birth of Hot Bigbang Universe
 14

Length Scales of Inflationary Universe
 log L End of Inflation
L=H0-1
 superhorizon scales
 k2
  H 2

 a2
 Size of the
 observable
 L=H-1 universe

 k2
 subhorizon scales  H 2

 a2
 log a(t)
 Inflationary Universe Bigbang Universe
 15

Generation of curvature perturbation
 scalar field vacuum fluctuation (on “flat” slices): f (on “superhorizon”)
 k2 k2
  f ,k  3H f ,k  2  f ,k  0 :  f ,k  const . as 2 2  0
 a (t ) H a
 comoving curvature perturbation Rc ~ - Newton potential
•  is frozen on “flat” (R=0) 3-surface (t=const. hypersurface)
 H
• Inflation ends/damped osc starts on  =const. 3-surface.   f
 
 c

 t
 T  const.,  c 0
 hot bigbang universe
  0
 
   0
end of  0
inflation
    f  0 
   0
 xi 16

Intermission: going back and forth…
 Nuffield Workshop
 June-July 1982

 apparently, a lot of confusion
 even among “big names”.

 The history of the derivation of the spectrum of adiabatic perturbations in new inflation,
 as presented in the talk by M.S. Turner at the Nuffield workshop in June 1982. To the best
 of my knowledge, the only person who did not change his results during the workshop
 was Alexei Starobinsky.

 figure and text: courtesy of V. Mukhanov 17

Curvature Perturbation Formula
 now often
 Mukhanov-Sasaki variable: m
 denoted by z

 at MD stage
 3(1  w) 3
   m for w  0
 3w  5 5

  
 v  a  a (a  Ha)
 a m
 H
 m
 18

Theoretical Predictions
• Amplitude of curvature perturbation:

 H2
 c  Mukhanov (1985), MS (1986)
 2 k /a  H

• Power spectrum index: M pl 
 1
 ~ 2.4 1018 GeV: Planck mass
 8 G
 2
 4 k H  2  V  V 2 
 3 2
 nS 1
 P (k )     Ak ; nS  1  M P  2 3 2 
 ( 2 )3 S
  2  k /a  H  V V 
 Stewart-Lyth (1993)
• Tensor (gravitational wave) spectrum:
 4 k 3 1 PS (k ) r
 P ( k )  Ak nT
 ; n     Liddle-Lyth (1992)
 (2 )3
 T T
 8 PT (k ) 8
 “consistency relation” 19

Progress in Particle Cosmology (3)
 3rd stage: 1995~ 2015
• 1995 Hubble Deep Field: z ~ 4-5
• 1998 2dF Galaxy Redshift Survey
 3x105 galaxies, z~0.2
• 1998 Accelerated Expansion (SCP/HZT)
• 2003 Accurate CMB angular spectrum (WMAP)
 Confirming Flatness of the Universe
 Strong evidence for Dark Energy
• 2005~
 2005~ Cosmic
 Cosmic (String Theory)Landscape
 (String Theory) Landscape!
• 2000~ SDSS I/II/III, 2014- SDSS-IV, …
 > 106 galaxies, high precision LSS data
• 2013 High precision CMB spectrum (Planck)
 Very strong evidence for Inflation
 20

CMB anisotropy spectrum
 Planck 2015 XI

 LCDM

 21

Planck+LSS constraints on inflation
 Planck 2015 XX

 V  2

 d log[k 3 PS (k )]
 ns  1 
 scalar spectral index: ns ~ 0.96 d log k
 tensor-to-scalar ratio: r < 0.1 r
 PT (k )
 simplest V   2 model is almost excluded PS (k )
 22

Summary: Current Status
 Standard (single-field, slow-roll) inflation predicts almost scale-
 invariant Gaussian curvature perturbations.
 Observational data are consistent with theoretical predictions.
• almost scale-invariant spectrum: nS  0.965  0.005 (68% CL)
• highly Gaussian fluctuations: f NL
 local
  2.5  5.7 (68% CL)
 3 local 2
  gauss  f NL gauss 
 5
 Simple standard models seem to be almost excluded…
• detection of f NL
 local
  O(1) would kill all the standard models.
 Tensor (gravitational wave) perturbation remains to be detected
 P (k ) 
 r T ~ 0.05
 PS (k) 23

Progress in Particle Cosmology (4)
 4th stage: 2015 ~ 20??
• 2015 First detection of GWs from Binary Black Holes (LIGO)
 Dawn of GW Astronomy
• 2017 First detection of GWs & EMWs from Binary Neutron Stars
 Multi-messenger Astronomy (LIGO+VIRGO)
• 2020+ Upgraded LIGO+VIRGO +KAGRA start operating
• 2020+ Deep & Wide LSS surveys (HSC-SSP/LSST/… )
 Data precision will reach

signature of primordial GWs
spacetime(~graviton) vacuum fluctuations from inflation
 GWs: quadrupolar in nature Starobinsky (1979)

 B-mode polarization in CMB anisotropy
 Seljak & Zaldarriaga (1996)

 • E-mode (even parity)

 • B-mode (odd parity)
 = cannot be produced from
 density fluctuations

 25

Cosmic Landscape/Multiverse?
string theory suggests an intriguing picture of the early universe

 taken from http://ineedfire.deviantart.com/art/Psychedelic-Multiverse-104313536

 Maybe we live in one of these vacua…
 26

27

 Swampland conjecture?
 ∇ < / ; = (1) Obied, Ooguri, Spodyneiko & Vafa ‘18

 ∇ < / ; = (1)
 Ooguri, Palti, Shiu & Vafa ‘18
or
 − ′ 
 min(∇ ∇ ) ≤ 2 ; ′ = (1)
 
 In particular, de Sitter (dS) space is in swampland!
 If dS exists in nature,
 either swampland conjecture is false
 or string theory is false !

 let us assume (hope?) that the conjecture is false!

Universe jumps around string landscape by quantum tunneling
 expansion rate
 • it can go up to a vacuum with larger v
 de Sitter (dS) space ~ thermal state with T =H/2
 SO(4,1)
 • if tunnels to a vacuum with v 0
 • inside a bubble with v >0 is Open dS universe
 SO(3,1)
 v multiverse!

0
 Sato, Kodama, MS & Maeda (’81)
 28

What if this is the case?
 a few possibilities N: number of e-folds
 1. inflation after tunneling was short enough (N~60)
 2 3
 K ,0  1  0  10 ~ 10 “open universe”
 signatures in large angle CMB anisotropies?
 Kanno, MS & Tanaka (‘13), White, Zhang & MS (’14), …

 2. inflation after tunneling was long enough (N>>60)
  K ,0  1  0 1 “flat universe”
 signatures from bubble collisions
 Sugimura, Yamauchi & MS (‘12), …

 3. quantum entanglement among multiverse?
 Maldacena & Pimentel (’13), Kanno (‘14), …
 29

length scales in open inflation
 current comoving
 Hubble radius

 curvature radius
 log L
 break scale in P(k)

 H-1

 log N

 curvature fast-roll phase slow-roll phase
dominated phase
 30

Inflationary cosmology in 21st Century
  High Precision Cosmology
 • gravitational waves from Inflation
 • extra dimensions / string cosmology
 • origin of dark energy
 • ···
 Gravitational Wave Astronomy has begun
 • LIGO (+VIRGO) detected GWs from BH & NS binaries
 Era of Multi-messenger Astronomy
 fundamental laws of nature may be revealed.
 (“ultimate” theory?)
 inflation = testbed for ultimate theory
 31