Title with LASS picture

Concluding remarks

Angel M. UrangaCERN, Geneva and IFT, Madrid

LASS 2007

String theory has come a long way...From the simple description of oscillating

strings that interact via pants ...

To the strange world of compactificationor the intriguing crossroads of string duality

Supergravity

Conformal field theory

Surprising maths

Branes

Dualities

Quantum GravityBlack holes

Theory of strong interactions in old

and new avatar

Theory ofall interactions

String theory has come a long way...

Useful to recall development of the fieldAnd it is the theory who has guided us most of the way

Theory of strong interactions,but spin 2 mode

Beautiful maths:Calabi-Yau geometry,

mirror symmetry

Theory of quantum gravity,but 10d and supersymmmetry

But moduli...

Compactification,extra dimensions

Supersymmetry andSupergravity

New model buildingusing D-branes

AdS/CFT and holographystrong interactions again!

New views on black holes

Flux compactifications andlandscape of vacua

Beyond perturbation theory:branes, dualities and all that

D-branes

Future of string theory?

IRHorizon UV

boundary

e.g. confinement in terms of dual black holes!

String theory, via the gauge/gravity correspondence has provided new ways to think about strongly coupled gauge theories, leading to a new picture of IR QCD

Strings and QCD

This picture is leading to quantitative characterization of the quark gluon plasma in heavy ion collisions in RHIC, and soon in ALICE at LHC

• Drag force when heavy quark moves through plasma • Etc ...

The hot QCD connection

• Low viscosity/entropy ratio !1

4π

Even some extreme quantitative agreements

Choptuik critical exponents in black hole formationMBH ! (p − p

∗)2γ

Critical exponent of saturation in Pomeron exchange

γ5d = 0.412 ± 1%

γBFKL = 0.4095

!k2

!k1

saturation scale =

(

|!k1|

|!k2|

)γ

Probably many more surprises to come!

Alvarez-Gaume, Gomez, Vazquez-Mozo

To achieve decoupling of scales, need to go beyond supergravity approximation

⇒ Need string theory in backgrounds with RR fluxAdS5 × S

5 may be within reach via modern techniques (pure spinors)

Some open questions

ΛIR ! MUV e−

1

gsN

Berkovits

• All gauge/string duals are infrared deformations of theories which are asymptotically conformal/AdS

• Need to identify quantities which are robust within universality class

Decisive step towards solving the information problem

Quantum gravity String theory leads to succesful counting of number of

microscopic states for many supersymmetric (or nearly supersymmetric) black holes

Also, quantitative implementation of insightful ideas of black hole physics ➱ Holography

How do the properties of the holographic dimension appear? e.g. locality, etc⇒ Implications for spacetime as a derived concept

How do the microstates look like at strong coupling? (intriguing proposal: smooth horizonless geometries?)

Schwarzschild black hole as hydrogen atom of Quantum Gravity

• Need to extend to more realistic black holes

Some open questions• Detailed dictionaries need to be developed

Strings and Cosmology

- Flatness, homogeneity,...- Dark matter- Dark energy

The Standard Model of Cosmology ΛCDM explains evolution of our Universe in very good agreement with all observations (e.g. WMAP data)

Throat inflation

String theory leads to appealing microscopic scenarios of inflation, with a simple interpretation of the inflaton, and its flatness

String cosmology

D3 D3

Φ

Brane-antibrane inflation

Cosmic strings In many models of brane inflation, relic F- and D-

strings remain as cosmic strings, possibly observable in future CMB experiments

Much work to understand properties of string network

Some open questions

• Genuine predictions of stringy inflation and comparison with experiment

(e.g. non-Gaussianities in DBI inflation; networking properties of stringy cosmic strings)

• Need better understanding of time-dependent backgrounds and Big-Bang-like singularities (at similar level as we understand black holes)

• String cosmology and initial conditions?

• Dark matter? (susy LSP?...?) Dark energy? (fine tuned cosmological constant?)

Strings and Particle Physics

- Hierarchy- Why 3 families- Why gauge interactions- Parameters- ...

The Standard Model of Particle Physics describes the behaviour of particles in amzing agreement with all observations over a wide range of scales

Intersecting branes Heterotic models

E8 × E8

String theory leads to appealing constructions with low-energy physics very close to that of the (MS)SM

Stringy Standard Model(s)

Much progress in understanding the origin of qualitative features of the SM: chiral matter, multiple families, gauge and Yukawa couplings

• Long-standing problems in this are being addressed Moduli stabilization, supersymmetry breaking

• Need a similar insight towards quantitative statements- How to achieve a specific texture of fermion masses- estimate of patterns of eg soft masses in susy- ...

The LHC effect

In Fall 2007 the LHC accelerator starts running

How can string theory and LHC talk to each other?

String theory underlies some of the best motivated scenarios for physics beyond the SM, that will be searched for at LHC- Supersymmetry- Large extra dimensions- Warped extra dimensions

In fact, they are already talking to each other

LHC will tell us which idea is correct, thus helping in future string model building(Still possible that real answer is something nobody thought about ...)

Afraid of the anthropic landscape?

Maybe but...Analogy with general relativity: Existence of many solutions does not bother us...`Just’ a matter of describing the right one

(really need to address the `why’?)

Many many many vacua of string theory(characterization is ongoing)

- Not likely to determine unique vacuum from first principles- No predictivity in the theory?

- Forced to study full string landscape? (statistics)- Need anthropic principle?

Main driving force up to now: understand the theory (already quite mature, although still quite Mysterious)

Much has been learned over the years

Next additional driving force: Understand relation with the world (cosmology, beyond SM, hot QCD, ...)

String theory is in good shape

Future of string theory?

...is in the young generation of students who is just starting to learn how to play with strings

Future of string theory...

Painting by Pamela Murphywww.pamelamurphystudio.