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Cosmology Now and Tomorrow. Misao Sasaki (YITP, Kyoto University). KASI-YITP Joint-Workshop: Cosmology Now and Tomorrow 17 -18 Feb 2012. Cosmology Now and Tomorrow. Misao Sasaki (YITP, Kyoto University). KASI-YITP Joint-Workshop: Cosmology Now and Tomorrow 17 -18 Feb 2012.

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Cosmology now and tomorrow

Cosmology Now and Tomorrow

Misao Sasaki

(YITP, Kyoto University)

KASI-YITP Joint-Workshop:

Cosmology Now and Tomorrow

17 -18 Feb 2012

Cosmology now and tomorrow1

Cosmology Now and Tomorrow

Misao Sasaki

(YITP, Kyoto University)

KASI-YITP Joint-Workshop:

Cosmology Now and Tomorrow

17 -18 Feb 2012


Cosmology now and tomorrow2

Cosmology Now and Tomorrow

Misao Sasaki

(YITP, Kyoto University)

KASI-YITP Joint-Workshop:

Cosmology Now and Tomorrow

17 -18 Feb 2012


– personal, biased perspective –

Current status
current status

  • big bang theory has been firmly established

CMB spectrum at T=2.725K

  • strong evidence for inflation

only to be confirmed (by tensor modes?)

  • “standard model”


WMAP 7yr

Current and future issues
current and future issues

I. GR cosmology

  • perturbation theory

  • numerical cosmology

I do NOT touch Dark Energy/Modified Gravity

recent developments in MG

→ R Kimura

II. Inflation

  • multi-field, non-canonical/minimal

  • conformal frame (in-)dependence

III. String Theory Landscape

  • observational signatures?

I gr cosmology
I. GR Cosmology

  • perturbation theory

linear theory has been extremely successful over the past 20-30 years

quantization and evolution of perturbations from inflation

single-field slow-roll inflation

Mukhanov ’85, MS ’86,...

Lyth-Liddle ’92, Stewart-Lyth ‘93

CMB anisotropy

Sunyaev & Zeldovich ’70, ....



conformal distance to

Last Scattering Surface

WMAP 7yr

growth of density perturbations (>~ 10 Mpc)

Peebles ’80, ..., Wang & Steinhardt ‘98


only a few papers, a lot to be done

  • need for NL theory is growing

Non-gaussianity from inflation

testing/constraining models of inflation

2nd and higher order perturbation theory

→ JC Hwang

higher order effects in CMB spectrum

no systematic studies, need to be developed

Naruko et al. in progress

(NL) GR effects on cosmological observables

Meures & Bruni ‘11, Jeong, Schmidt & Hirata ’11,...


practically nothing has been done yet

inhomogeneous universe models

  • Numerical GR Cosmology

testing TLB (anti-Copernican) model

quantifying GR effects in LSS formation


perturbative? Post Newtonian?

BH universe

BH dominated (“vacuum”) universe

→ CM Yoo

(primordial) BH formation

Shibata & MS ’99, ...(but spherically sym)

2D & 3D codes to be developed

Ii inflation
II. Inflation

  • multi-field/non-canonical/non-minimal models

  • PLANCK will announce the first result by Feb 2013,

    exactly 1 year from now. So be prepared !

  • construct as many models as possible which are

    compatible with current WMAP data, and which can be

    tested by PLANCK etc. (not too distant future)

spectral index, tensor perturbation, non-Gaussianity,

ad-iso correlation, primordial BH,...

→ Alabidi, Saito, Stewart, Yamaguchi

any other new signatures?

Makino & MS ‘91, ... ,

Gong, Hwang, Park, MS & Song ‘11

  • Linear theory

  • conformal (in-)dependence of cosmological perturbations

tensor-type perturbation

Definition of hijis apparently W-independent.

vector-type perturbation

Definitions of Bjand Hjare asloW-independent.

tensor & vector perturbations are

conformal frame-independent

scalar-type perturbation

Definitions of B and E are W-independent.

But AandRare W-dependent!


  • The important, curvature perturbation Rc , conserved on

    superhorizon scales, is defined on comoving hypersurfaces.

uniform f (df = 0)


if W=W(f)

  • For scalar-tensor theory with

we have

Rc=Rdf=0 is W-independent!

generalization to nonlinear case is straightforward



  • multi-component case

general case is discussed in Gong et al. (’11)

  • Is distinction between adiabatic and isocurvature

    perturbations conformally invariant?

Yes, if we consider trajectories

in field space, because it is



But this assumes reduction

of phase space to field space:

The assumption seems violated in general, eg, when

different comps have different curvature couplings.

→ Minamitsuji & White, in progress

Iii string theory landscape
III. String theory landscape



Lerche, Lust & Schellekens (’87), Bousso & Pochinski (’00),

Susskind, Douglas, KKLT (’03), ...

  • There are ~ 10500 vacua in string theory

  • vacuum energy rv may be positive or negative

  • typical energy scale ~ MP4

  • some of them have rv <<MP4



Is there any way to know what kind of landscape we live in?

Or at least to know what kind of

neighborhood we live in?

Distribution function in flux space
distribution function in flux space

Vacua with enhanced gauge symmetry

by courtesy of T. Eguchi

may explain the origin of gauge symmetry

(SU(3)xSU(2)xU(1)) in our Universe

De sitter ds anti de sitter ads
de Sitter (dS) & Anti-de Sitter (AdS)

  • dS space: rv>0, O(4,1) symmetry

  • AdS space: rv<0, O(3,2) symmetry

collapses within t~1/H



  • A universe jumps around in the landscape by quantum


  • it can go up to a vacuum with larger rv

( dS space ~ thermal state with T =H/2p )

  • if it tunnels to a vacuum with negative rv ,

    it collapses within t ~ MP/|rv|1/2.

  • so we may focus on vacua with positive rv: dS vacua


Sato, MS, Kodama & Maeda (’81)


  • Anthropic landscape

  • Not all of dS vacua are habitable.

“anthropic” landscape

Susskind (‘03)

  • A universe jumps around in the landscape and settles

    down to a final vacuum with rv,f ~ MP2H02 ~(10-3eV)4.

rv,f must notbe larger than this value in order to

account for the formation of stars and galaxies.

  • Just before it has arrived the final vacuum (=present universe), it must have gone through an era of (slow-roll) inflation and reheating, to create “matter and radiation.”

rvac → rmatter ~ T4: birth of Hot Bigbang Universe

false vacuum decay via O(4) symmetric (CDL) instanton

Coleman & De Luccia (‘80)

O(4) O(3,1)

inside bubble is an open universe

bubble wall

false vacuum

Creation of open universe
creation of open universe

open (hyperbolic) space

bubble wall

analytic continuation


  • Natural outcome would be a universe with W0 <<1.

  • “empty” universe: no matter, no life

  • Anthropic principle suggests that # of e-folds of inflation

    inside the bubble (N=HDt) should be ~ 50 – 60 : just

    enough to make the universe habitable.

Garriga, Tanaka & Vilenkin (‘98), Freivogel et al. (‘04)

  • Observational data excluded open universe with W0 <1.

  • Nevertheless, the universe may be slightly open:

may be tested by PLANCK+BAO

Colombo et al. (‘09)

What if 1-W0 is actually confirmed

to be non-zero:~10-2 -10-3?

revisit open inflation!

see if we can say anything about


effect of tunneling on large angular scale CMB

Yamauchi, Linde, Naruko, MS & Tanaka ’11

CMB cold/hot spots = bubble collision?

Aguirre & Johnson ’09, Kleban, Levi & Sigurdson ’11,...

Non-Gaussianity from bubbles?

Blanco-Pillado & Salem ’10, Sugimura et al. in progress

Tunneling probability / resonant tunneling?

Tye & Wohns ’09, Brown & Dahlen ‘11

Measure problem?

Garriga & Vilenkin ‘08, Freivogel ’11, Vilenkin ’11, ....

any others?


  • develop GR cosmology further:

perturbative, non-perturbative, numerical, observational...

(GR can be replace by MG)

  • propose testable inflation models

non-minimal, non-canonical, multi-field, ....

  • look for signatures of string theory landscape

................ ! ... ?