Pentahedral Volume, Chaos, and Quantum Gravity

Transcription

1 Pentahedral Volume, Chaos, and Quantum Gravity Hal Haggard May 30, 2012

2 Volume Polyhedral Volume (Bianchi, Doná and Speziale): ˆV Pol = The volume of a quantum polyhedron

3 Outline 1 Pentahedral Volume 2 Chaos & Quantization 3 Volume Dynamics and Quantum Gravity

4 Outline 1 Pentahedral Volume 2 Chaos & Quantization 3 Volume Dynamics and Quantum Gravity

5 Minkowski s theorem: polyhedra The area vectors of a convex polyhedron determine its shape: A A n = 0.

6 Minkowski s theorem: polyhedra The area vectors of a convex polyhedron determine its shape: A A n = 0. Only an existence and uniqueness theorem.

7 Minkowski s theorem: a tetrahdedron Interpret the area vectors of tetrahedron as angular momenta: A 1 + A 2 + A 3 + A 4 = 0 For fixed areas A 1,..., A 4 each area vector lives in S 2. Symplectic reduction of (S 2 ) 4 gives rise to the Poisson brackets: {f, g} = 4 l=1 ( f A l A g ) l A l

8 Minkowski s theorem: a tetrahdedron For fixed areas A 1,..., A 4 p = A 1 + A 2 q = Angle of rotation generated by p: {q, p} = 1

9 Dynamics Take as Hamiltonian the Volume: H = V 2 = 2 9 A 1 ( A 2 A 3 )

10 Bohr-Sommerfeld quantization Require Bohr-Sommerfeld quantization condition, S = pdq = (n )2π. γ Area of orbits given in terms of complete elliptic integrals, ( 4 ) 4 S(E) = a i K(m) + b i Π(αi 2, m) E i=1 i=1

11 V Tet = A 1 ( A 2 A 3 ) A 1 = j + 1/2 A 2 = j + 1/2 A 3 = j + 1/2 A 4 = j + 3/2 4 2 = Numerical = Bohr-Som [PRL 107, ]

12 Table j 1 j 2 j 3 j 4 Loop gravity Bohr- Accuracy Sommerfeld % % % % % % % % % % % %

13 Volume of a pentahedron A pentahedron can be completed to a tetrahedron

14 Volume of a pentahedron A pentahedron can be completed to a tetrahedron α, β, γ > 1 found from, α A 1 + β A 2 + γ A 3 + A 4 = 0 e.g. = α = A 4 ( A 2 A 3 )/ A 1 ( A 2 A 3 )

15 Volume of a pentahedron A pentahedron can be completed to a tetrahedron The volume of the prism is then, 2 ( ) V = αβγ (α 1)(β 1)(γ 1) A 1 ( A 3 2 A 3 )

16 Adjacency and reconstruction What s most difficult about Minkowski reconstruction? Adjacency! Remarkable side effect of introducing α, β and γ: they completely solve the adjacency problem!

17 Determining the adjacency Let W ijk = A i ( A j A k ). Different closures imply, α 1 A1 + β 1 A2 + γ 1 A3 + A 4 = 0, α α 1 = W 234 W 123 β β 1 = W 134 W 123 γ γ 1 = W 124 W 123 α 2 A1 + β 2 A2 + A 3 + γ 2 A4 = 0, α 2 = W 234 W 124 = α γ β 2 = W 134 W 124 = β γ γ 2 = W 123 W 124 = 1 γ They are mutually incompatible!

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19 Cylindrical consistency Smaller graphs and the associated observables can be consistently included into larger ones Cylindrical consistency is non-trivially implemented for the polyhedral volume

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22 Outline 1 Pentahedral Volume 2 Chaos & Quantization 3 Volume Dynamics and Quantum Gravity

23 EBK quantization Sommerfeld and Epstein extended Bohr s condition, L = n, as we have seen T S = p dq dt = nh dt 0 and applied it to bounded, separable systems with d degrees of freedom, Ti 0 p i dq i dt dt = n ih, i = 1,..., d Here the T i are the periods of each of the coordinates. Einstein(!) was not satisfied. These conditions are not invariant under phase space changes of coordinates.

24 EBK quantization II Motivating example: central force problems In configuration space trajectories cross

25 EBK quantization II Motivating example: central force problems Momenta are distinct at such a crossing

26 EBK quantization II Motivating example: central force problems In phase space the distinct momenta lift to the two sheets of a torus

27 EBK quantization III Following Poincaré, Einstein suggested that we use the invariant d p i dq i i=1 to perform the quantization. The topology of the torus remains under coordinate changes, and so the quantization condition should be, S i = p d q = n i h. C i

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29 Surface of section Visualizing dynamics with a surface of section

30 KAM: Weak perturbation of an integrable system Break up of those tori foliated by trajectories with rational frequency ratios

31 KAM: Weak perturbation of an integrable system Break up of those tori foliated by trajectories with rational frequency ratios Toroidal Islands and island chains are left within a sea of chaos

32 Outline 1 Pentahedral Volume 2 Chaos & Quantization 3 Volume Dynamics and Quantum Gravity

33 Phase space of the pentahedron I The pentahedron has two fundamental degrees of freedom, The angles generated by p 1 = A 1 + A 2 and p 2 = A 3 + A 4.

34 Phase space of the pentahedron II For fixed p 1 and p 2 these angles sweep out a torus. The phase space consists of tori over a convex region of the p 1 p 2 -plane.

35 Volume is nonlinear The volume is a very nonlinear function of any of the variables we have considered: 2 ( ) V = αβγ (α 1)(β 1)(γ 1) A 3 1 ( A 2 A 3 ) Recall, α = A 4 ( A 2 A 3 ) A 1 ( A 2 A 3 ), similarly for β, γ Forced to integrate it numerically.

36 Numerical integration Fortunately, the angular momenta can be lifted into the phase space of a collection of harmonic oscillators. This allows the use of a geometric (i.e. symplectic) integrator. Explicit Euler: u n+1 = u n + h a(u n ) Implicit Euler: u n+1 = u n + h a(u n+1 ) Symplectic Euler: u n+1 = u n + h a(u n, v n+1 ) v n+1 = v n + h b(u n, v n+1 ) Implementation: Symplectic integrator preserves face areas to machine precision and volume varies in 14th digit

37 Volume dynamics: first results A Schlegel diagram projects a 3D polyhedron into one of its faces (left panel): A Schlegel move merges two vertices of the diagram and and splits them apart in a different manner. This is precisely how the volume dynamics changes adjacency.

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39 Poincaré section of pentahedral volume dynamics

40 Guess: Analogy with billiards systems suggests that the dynamics will be mixed, containing chaos

41 Conclusions Minkowski reconstruction for 5 vectors solved There is cylindrical consistency in the polyhedral picture and it is non-trivial The classical polyhedral volume is only twice continuously differentiable Can explore the classical dynamics of the volume operator in the case of a polyhedron with 5 faces Does this dynamics exhibit chaos?