lecture by pietro frè and alexander s. sorin
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Full Integrability of Supergravity Billiards: the arrow of time, asymptotic states and trapped surfaces in the cosmic evolution. Lecture by Pietro Frè and Alexander S. Sorin In connection with the nomination for the JINR prize 2008. - PowerPoint PPT PresentationTRANSCRIPT
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Full Integrability of Supergravity Billiards:
the arrow of time, asymptotic states and trapped surfaces in the cosmic evolution
Lecture by Pietro Frè andAlexander S. Sorin
In connection with the nomination for the JINR prize 2008
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Standard Cosmology Standard
cosmology is based on the cosmological principle.
Homogeneity Isotropy
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Evolution of the scale factorwithout cosmological
constant
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From 2001 we know that the Universe is spatially flat (k=0) and
that it is dominated by dark energy.
Most probably there has been inflation
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The scalar fields drive inflation while rolling down from a maximum to a minimum
• Exponential expansion during slow rolling
• Fast rolling and exit from inflation
• Oscillations and reheating of the Universe
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The isotropy and homogeneity are proved by
the CMB spectrum
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WMAP measured anisotropies of CMB
The milliKelvin angular variations of CMB temperature are the inflation blown upimage of Quantum fluctuations of the gravitational potential and the seeds of large scale cosmological structures
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Accelerating Universe dominated by Dark Energy
Equation of State
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Non isotropic Universes This is what happens if there is
isotropy ! Relaxing isotropy an entire new
world of phenomena opens up In a multidimensional world, as string
theory predicts, there is no isotropy among all dimensions!
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Cosmic Billiards before 2003A challenging phenomenon, was proposed, at the beginning of this millenium, by a number of authors under the name of cosmic billiards. This proposal was a development of the pioneering ideas of Belinskij, Lifshits and Khalatnikov, based on the Kasner solution of Einstein equations. The Kasner solution corresponds to a regime, where the scale factors of a D-dimensional universe have an exponential behaviour . Einstein equations are simply solved by imposing quadratic algebraic constraints on the coefficients . An inspiring mechanical analogy is at the root of the name billiards.
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Some general considerations on roots and gravity.......
String Theory implies D=10 space-time dimensions.
Hence a generalization of the standard cosmological metric is of the type:
In the absence of matter the conditions for this metric to be Einstein are:
Now comes an idea at first sight extravagant.... Let us imagine that
are the coordinates of a ball moving linearly with constant velocity
What is the space where this fictitious ball moves
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ANSWER:The Cartan subalgebra of a rank 9 Lie algebra.
h1
h2
h9
What is this rank 9 Lie algebra?
It is E9 , namely an affine extension of the Lie algebra E8
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Lie algebras and root systems
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Lie algebras are classified.......by the properties of simple roots. For instance for A3 we have 1, 2 , 3 such that...........
1
23
2+3
1+2
1+2 +3
It suffices to specify the scalar products of simple roots
And all the roots are given
For instance for A3
There is a simple way of representing these scalar
products:Dynkin diagrams
1 2 3
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Algebras of the type
4
1 6 5 3 2 1
1 2 1
exist for any
Algebras of the type exist only for
E series (exceptional)
In an euclidean space we cannot fit more than 8 linear independent vectors with angles of 120 degrees !!The group Er is the duality group of String
Theory in dimension D = 10 – r + 1
In D=3 we have E8
Then what do we have for D=2 ?
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We have E9 !How come? More than 8 vectors cannot be fitted in an euclidean space at the prescribed angles !
Yes! Euclidean!! Yet in a non euclidean space we can do that !!
Do you remember the condition on the exponent pi = (velocity of the little ball)
where
If we diagonalize the matrix Kij we find the eigenvalues
Here is the non-euclidean signature in the Cartan subalgebra of E9. It is an infinite dimensional algebra ( = infinite number of roots!!)
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Now let us introduce also the roots......
h1
h2
h9
There are infinitely many, but the time-like ones are in finite number. There are 120 of them as in E8. All the others are light-like
Time like roots, correspond to the light fields of Superstring Theory different from the diagonal metric: off-diagonal components of the metric and p-form fields
When we switch on the roots, the fictitious cosmic ball no longer goes on straight lines. It bounces!!
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The cosmic Billiard
The Lie algebra roots correspond to off-diagonal elements of the metric, or to matter fields (the p+1 forms which couple to p-branes)
Switching a root we raise a wall on which the cosmic ball bounces
Or, in frontal view
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Before 2003: Rigid Billiards
h-space CSA of the U algebra
walls hyperplanes orthogonalto positive roots (hi)
bounces Weyl reflections
billiard region Weyl chamber
The Supergravity billiard is completely determined by U-duality group
Smooth billiards:
Asymptotically any time—dependent solution defines a zigzag in ln ai space
Damour, Henneaux, Nicolai 2002 --
Exact cosmological solutions can be constructed using U-duality (in fact billiards are exactly integrable)
bounces Smooth Weyl reflections
walls Dynamical hyperplanes
Frè, Sorin,
and collaborators, 2003-2008
series of papers
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What is the meaning of the smooth cosmic billiard ?
• The number of effective dimensions varies dynamically in time!
• Some dimensions are suppressed for some cosmic time and then enflate, while others contract.
• The walls are also dynamical. First they do not exist then they raise for a certain time and finally decay once again.
• The walls are euclidean p-branes! (Space-branes)
• When there is the brane its parallel dimensions are big and dominant, while the transverse ones contract.
• When the brane decays the opposite occurs
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Cosmic Billiards in 2008 The billiard phenomenon is the generic feature of all exact solutions of
supergravity restricted to time dependence. We know all solutions where two scale factors are equal. In this case
one-dimensional model on the coset U/H. We proved complete integrability.
We established an integration algorithm which provides the general integral.
We discovered new properties of the moduli space of the general integral. This is the compact coset H/Gpaint , further modded by the relevant Weyl group. This is the Weyl group WTS of the Tits Satake subalgebra UTS ½ U.
There exist both trapped and (super)critical surfaces. Asymptotic states of the universe are in one-to-one correspondence with elements of WTS.
Classification of integrable supergravity billiards into a short list of universality classes.
Arrow of time. The time flow is in the direction of increasing the disorder:
Disorder is measured by the number of elementary transpositions in a Weyl group element.
Glimpses of a new cosmological entropy to be possibly interpreted in terms of superstring microstates, as it happens for the Bekenstein-Hawking entropy of black holes.
Results established by P.Frè and A.Sorin
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Main PointsDefinition
Statement
Because t-dependentsupergravity field equationsare equivalent to thegeodesic equations fora manifold
U/H
Because U/H is alwaysmetrically equivalent toa solvable group manifold exp[Solv(U/H)]and this defines acanonical embedding
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What is a - model ?It is a theory of maps from one manifold to another one:
World manifold W:coordinates
Target manifold M:
coordinates I
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Starting from D=3 (D=2 and D=1, also) all the (bosonic) degrees of freedom are scalars
The bosonic Lagrangian of both Type IIA and Type IIB reduces, upon toroidal dimensional reduction from D=10 to D=3, to the gravity coupled sigma model
)16()8(8
SOE
targetM With the target manifold being the maximally non-compact coset space
8
5
1 2 3 4 6 7
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The discovered PrincipleThe relevantWeyl group is thatof the Tits Satakeprojection. It isa property of a universality class of theories.
There is an interesting topology of parameter space for the LAX EQUATION
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The Weyl group of a Lie algebra• Is the discrete group generated by all
reflections with respect to all roots• Weyl(L) is a discrete subgroup of the
orthogonal group O(r) where r is the rank of L.
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The mathematical ingredients Dimensional reduction to D=3 realizes the
identification SUGRA = -model on U/H The mechanism of Kac Moody extensions The solvable parametrization of non-
compact U/H The Tits Satake projection The Lax representation of geodesic
equations and the Toda flow integration algorithm
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Full IntegrabilityLax pair representation
and the integration algorithm
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Lax Representation andIntegration Algorithm
Solvable cosetrepresentative
Lax operator (symm.)
Connection (antisymm.)
Lax Equation
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Parameters of the time flows
From initial data we obtain the time flow (complete integral)
Initial data are specified by a pair: an element of the non-compact CartanSubalgebra and an element of maximal compact group:
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Properties of the flowsThe flow is isospectral
The asymptotic values of the Lax operator are diagonal (Kasner epochs)
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Proposition
Trappedsubmanifolds
ARROW OFTIME
Parameter space
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Example. The Weyl group of
Sp(4)» SO(2,3)
Available flowson 3-dimensionalcritical surfaces
Available flows on edges, i.e. 1-dimensional critical surfaces
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An example of flow on a critical surface for SO(2,4). 2 , i.e. O2,1 = 0
Future
PAST
Plot of 1 ¢ hPlot of 1 ¢ h
Future infinity is 8 (the highest Weyl group element), but at past infinitywe have 1 (not the highest) = criticality
Zoom on this region
Trajectory of the cosmic ball
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Future
PAST
Plot of 1 ¢ h
Plot of 1 ¢ h
O2,1 ' 0.01 (Perturbation of
critical surface)
There is an extra primordialbounce and we have the lowest Weyl group element 5 at
t = -1
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END of this RECITALThank you for your
attention
In case of request of request…..there is encore…..
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For subject lovers
More details on the underlying
Mathematical Structure
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Duality AlgebrasThe algebraic structure of duality
algebras in D<4dimensions
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Structure of the Duality Algebra in D=3
Universal, comes from Gravity
Comes from
vectors in D=4
Symplectic metric in d=2 Symplectic metric in 2n dim
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Affine and Hyperbolic algebrasand the cosmic billiard
We do not have to stop to D=3 if we are just interested in time dependent backgrounds
We can step down to D=2 and also D=1 In D=2 the duality algebra becomes an
affine Kac-Moody algebra In D=1 the duality algebra becomes an
hyperbolic Kac Moody algebra Affine and hyperbolic symmetries are
intrinsic to Einstein gravity
(Julia, Henneaux, Nicolai, Damour)
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N=8 E8(8)
N=6 E7(-5)
N=5 E6(-14)
N=4
SO(8,n+2)
N=3
SU(4,n+1)
Duality algebras for diverse N(Q) from D=4 to D=3
E7(7)
SO*(12)
SU(1,5)
SL(2,R)£SO(6,n)
SU(3,n) £ U(1)Z
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What happens for D<3?
7
9
5
6
8
4
7
3
6
2
5
1
4
8
3 D
Exceptional E11- D series for N=8 give a hint
E8
Julia 1981
2
E9 = E8Æ
UD
GL(2,R)SL(2) + SL(3)SL(5)
E4 E3
SO(5,5)
E5E6E7
0
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This extensions is affine!
UD=4
W0
The new triplet is connected to the vector root with a single line,since the SL(2)MM commutes with UD=4
2 exceptions: pure D=4 gravity and N=3 SUGRA
UD=4
W1
0
W2
0 1
The new affine triplet: (LMM0, LMM
+, LMM-)
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N=8 E8(8)
N=6 E7(-5)
N=5 E6(-14)
N=4
SO(8,n+2)
N=3
SU(4,n+1)
D=4
E7(7)
SO*(12)
SU(1,5)
SL(2,R)£SO(6,n)
SU(3,n) £ U(1)Z
E9(9)
E7
E6
SO(8,n+2)
D=3 D=2
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The Tits Satake projection
A fondamental ingredientto single out the universality
classes and the relevant Weyl group
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root system
of rank r1
ProjectionSeveral roots of the higher system have the same projection.These are painted copies of the same wall.The Billiard dynamics occurs in the rank r2 system
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Two type of roots
1
2
3
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To say it in a more detailed way:
Non split algebras arise as duality algebras in non maximal supergravities N< 8
r – split rank
Under the involutive automorphism that defines the non split real section
compact rootsnon compact rootsroot pairs
Non split real algebras are represented by Satake diagrams
For example, for N=6 SUGRAwe have E7(-5)
Compact simple rootsdefine a sugalgebraHpaint
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The paint group
The subalgebra of external automorphisms:
is compact and it is the Lie algebra of the paint group
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Paint group in diverse dimensions
The paint group survives under dimensional reduction, that adds only non-compact directions to the scalar manifold
D=3D=4
It means that the Tits Satake projection commutes with the dimensional reduction
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The SolvableParametrization
Crucial for integrability is the remarkable relation between
non-compact cosets U/H and
Solvable Group Manifolds exp[Solv]
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Solvable Lie Algebras: i.e. triangular matrices• What is a solvable Lie algebra A ?• It is an algebra where the derivative series ends after some steps• i.e. D[A] = [A , A] , Dk[A] = [Dk-1[A] , Dk-1[A] ]• Dn[A] = 0 for some n > 0 then A = solvable
THEOREM: All linear representations of a solvable Lie algebra admit a basis whereevery element T 2 A is given by an upper triangular matrix For instance the
upper triangular matrices of this
type form a solvable subalgebra
SolvN ½ sl(N,R)
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The solvable parametrizationThere is a fascinating theorem which provides an identification of the geometryof moduli spaces with Lie algebras for (almost) all supergravity theories.
THEOREM: All non compact (symmetric) coset manifolds are metrically equivalent to a solvable group manifold
• There are precise rules to construct Solv(U/H)• Essentially Solv(U/H) is made by
• the non-compact Cartan generators Hi 2 CSA K and• those positive root step operators E which are not orthogonal to the non
compact Cartan subalgebra CSA K
Splitting the Lie algebra U into the maximal compact subalgebra H plus the orthogonal complement K
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Maximally split cosets U/H U/H is maximally split if CSA = CSA K is
completelly non-compact Maximally split U/H occur if and only if SUSY
is maximal # Q =32. In the case of maximal susy we have (in D-
dimensions the E11-D series of Lie algebras For lower supersymmetry we always have
non-maximally split algebras U