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