# accelerating universes and the emerging landscape of string theory

Embed Size (px)

TRANSCRIPT

An Inflationary Model In String TheoryTheory

apart is increasing with time.

New Discovery

"for the discovery of the

accelerating expansion of the

suggests that the rate of expansion

should be slowing down. Not

Accelerating.

be dominating the universe.

It is called Dark Energy.

The acceleration is thought to be

driven by dark energy, but what that

dark energy is remains an enigma -

perhaps the greatest in physics

today.

is Accelerating?

• Cosmic Microwave background

Most of the Universe is made up of

unknown forms of matter and energy:

•67% : Dark Energy – completely

unfamiliar. Must have negative

LHC experiment that is now underway)

•4% Familiar Baryonic Matter.

2011 Nobel Laureates in

is unknown to science. And

everything is possible again.

Cosmic Microwave Background Radiation

•Discovered by Penzias and

any terrestrial experiment!

the Cosmic Microwave Background

sky have been measured, with a

precision:

NASA/WMAP science team

WMAP 7-Year Data

model with about six parameters

including:

Kowalski et. Al. Taken From Particle

Data Book

Dark Energy.

•If this energy is positive it gives rise

to acceleration

pressure.

Pressure

CMB, Green BAO (Kowalski et. Al. (2008)).

•Negative pressure is strange!

cause an implosion.

leads to acceleration!

•But required value 2X gm/cc very

small.

Cosmological Constant problem.

)29(10

(except for gravity).

calculate the answer.

from first principles we need a theory of

gravity consistent with the rules of

quantum mechanics.

Physics at the longest of distance

scales is intimately tied to physics

at the shortest of distance scales!

Another Motivation:

theory could not give rise to

accelerating universes.

Moduli Stabilisation.

Compactifications. (~100)

compact space

Internal

directions

Non-compact

directions

physical parameters, like

degeneracy.

degeneracy is lifted.

Moduli Stabilisation

Mechanics.

E.g.

lifts the classical degenracy.

is due to Supersymmetry.

supersymmetry must be broken

constant.

•But resulting potential is hard to

control.

be calculated one gets typically runaway like

situations.

minimum with a positive value for the

potential.

flat directions.

behavior in the potential.

Accelerating Universe and Moduli

•Turn on Fluxes along the small extra

directions.

(Including Higher Forms, )

on size and shape of compactification.

Internal

directions

Non-compact

directions

Any Value of R1,R2 Allowed: Moduli

R1

R2

sphere

S. Kachru, R. Kallosh, A.Linde,

S.P.Trivedi,

Result:

Constant Can Indeed Arise in String

Theory.

understanding these different

confidence that the construction, and

others like it, do make sense.

The Construction

said.

rigorously ensure deSitter vacua do

exist in string theory.

need a deeper understanding akin to

what we have today for negative

cosmological constant vacua.

Many, Many, Universes

different vacua.

•Preliminary estimate,

(Douglas, Denef,..).

thermal fluctuation in desitter space.

Bousso Polchinkski

Constant

natural units.

Cosmological Constant:

•But values very much bigger than the

one observed would not lead to life.

•Galaxies would not form. (Weinberg

1987).

•In what sense is this an explanation?

•Is it predictive?

the other constants of Nature as well?

•In what sense then is string theory

predictive?

Implications of the Landscape Cont’d

Personal Views:

of last resort.

symmetries, are superior because they are

predictive.

is no other reasonable explanation for the

cosmological constant.

string theory more fully.

time dependent situations

constants, especially small values.

help find vacua of the kind we live in

and allow us to test string theory.

• Cosmologists have discovered that the

universe is accelerating.

in string theory. Their construction is

based on turning on fluxes .

Summary

possibilities described by a landscape.

•And provides an unconventional

explanation for the cosmological

theoretical model characterised by

some value for , k,

and a few other

Personal Views:

many predictions.

thinking in particle physics, based on

symmetries, are quite likely to continue to

be of great relevance.

Six Parameters:

(reionisation depth)

100cr

1cr if W_0 <<1. With 10^(100) vacua this leaves

many possibilities.

•In what sense is String Theory

predictive?

Anthropic Principle?

Personal Views:

goals of string theory.

correct? For this we need to make a

prediction which is borne out.

apart is increasing with time.

New Discovery

"for the discovery of the

accelerating expansion of the

suggests that the rate of expansion

should be slowing down. Not

Accelerating.

be dominating the universe.

It is called Dark Energy.

The acceleration is thought to be

driven by dark energy, but what that

dark energy is remains an enigma -

perhaps the greatest in physics

today.

is Accelerating?

• Cosmic Microwave background

Most of the Universe is made up of

unknown forms of matter and energy:

•67% : Dark Energy – completely

unfamiliar. Must have negative

LHC experiment that is now underway)

•4% Familiar Baryonic Matter.

2011 Nobel Laureates in

is unknown to science. And

everything is possible again.

Cosmic Microwave Background Radiation

•Discovered by Penzias and

any terrestrial experiment!

the Cosmic Microwave Background

sky have been measured, with a

precision:

NASA/WMAP science team

WMAP 7-Year Data

model with about six parameters

including:

Kowalski et. Al. Taken From Particle

Data Book

Dark Energy.

•If this energy is positive it gives rise

to acceleration

pressure.

Pressure

CMB, Green BAO (Kowalski et. Al. (2008)).

•Negative pressure is strange!

cause an implosion.

leads to acceleration!

•But required value 2X gm/cc very

small.

Cosmological Constant problem.

)29(10

(except for gravity).

calculate the answer.

from first principles we need a theory of

gravity consistent with the rules of

quantum mechanics.

Physics at the longest of distance

scales is intimately tied to physics

at the shortest of distance scales!

Another Motivation:

theory could not give rise to

accelerating universes.

Moduli Stabilisation.

Compactifications. (~100)

compact space

Internal

directions

Non-compact

directions

physical parameters, like

degeneracy.

degeneracy is lifted.

Moduli Stabilisation

Mechanics.

E.g.

lifts the classical degenracy.

is due to Supersymmetry.

supersymmetry must be broken

constant.

•But resulting potential is hard to

control.

be calculated one gets typically runaway like

situations.

minimum with a positive value for the

potential.

flat directions.

behavior in the potential.

Accelerating Universe and Moduli

•Turn on Fluxes along the small extra

directions.

(Including Higher Forms, )

on size and shape of compactification.

Internal

directions

Non-compact

directions

Any Value of R1,R2 Allowed: Moduli

R1

R2

sphere

S. Kachru, R. Kallosh, A.Linde,

S.P.Trivedi,

Result:

Constant Can Indeed Arise in String

Theory.

understanding these different

confidence that the construction, and

others like it, do make sense.

The Construction

said.

rigorously ensure deSitter vacua do

exist in string theory.

need a deeper understanding akin to

what we have today for negative

cosmological constant vacua.

Many, Many, Universes

different vacua.

•Preliminary estimate,

(Douglas, Denef,..).

thermal fluctuation in desitter space.

Bousso Polchinkski

Constant

natural units.

Cosmological Constant:

•But values very much bigger than the

one observed would not lead to life.

•Galaxies would not form. (Weinberg

1987).

•In what sense is this an explanation?

•Is it predictive?

the other constants of Nature as well?

•In what sense then is string theory

predictive?

Implications of the Landscape Cont’d

Personal Views:

of last resort.

symmetries, are superior because they are

predictive.

is no other reasonable explanation for the

cosmological constant.

string theory more fully.

time dependent situations

constants, especially small values.

help find vacua of the kind we live in

and allow us to test string theory.

• Cosmologists have discovered that the

universe is accelerating.

in string theory. Their construction is

based on turning on fluxes .

Summary

possibilities described by a landscape.

•And provides an unconventional

explanation for the cosmological

theoretical model characterised by

some value for , k,

and a few other

Personal Views:

many predictions.

thinking in particle physics, based on

symmetries, are quite likely to continue to

be of great relevance.

Six Parameters:

(reionisation depth)

100cr

1cr if W_0 <<1. With 10^(100) vacua this leaves

many possibilities.

•In what sense is String Theory

predictive?

Anthropic Principle?

Personal Views:

goals of string theory.

correct? For this we need to make a

prediction which is borne out.