THETA FUNCTIONS AND KNOTS Răzvan Gelca

Transcription

1 THETA FUNCTIONS AND KNOTS Răzvan Gelca

2 THETA FUNCTIONS AND KNOTS Răzvan Gelca based on joint work with Alejandro Uribe and Alastair Hamilton

3 B. Riemann: Theorie der Abel schen Funktionen

4 Riemann s work on elliptic integrals (based on insights of Abel and Jacobi): Study integrals u(x) = R(x, y)dt where y(x) is defined by a polynomial equation P (x, y) = 0 (elliptic for P cubic or cuartic).

5 Riemann s work on elliptic integrals (based on insights of Abel and Jacobi): Switch to complex coordinates.

6 Riemann s work on elliptic integrals (based on insights of Abel and Jacobi): Switch to complex coordinates. Study line integrals u(x) = x a R(z(t), w(t))dt where w(z) is defined by a polynomial equation F (z, w) = 0.

7 Riemann s work on elliptic integrals (based on insights of Abel and Jacobi): Switch to complex coordinates. Study line integrals u(x) = x a R(z(t), w(t))dt where w(z) is defined by a polynomial equation F (z, w) = 0. Because w lives naturally on a Riemann surface.

8 Example: For the Weierstrass curve the Riemann surface is a torus: w 2 = z(z 1)(z λ)

9 Abel, Jacobi: It is more interesting to study the inverse functions of elliptic integrals.

10 Abel, Jacobi: It is more interesting to study the inverse functions of elliptic integrals. These are called elliptic functions.

11 Abel, Jacobi: It is more interesting to study the inverse functions of elliptic integrals. These are called elliptic functions. Elliptic functions are doubly periodic meromorphic functions; they live on tori.

12 Abel, Jacobi: It is more interesting to study the inverse functions of elliptic integrals. These are called elliptic functions. Elliptic functions are doubly periodic meromorphic functions; they live on tori. The building blocks of elliptic functions are theta functions.

13 Riemann surface ζ 1, ζ 2,..., ζ g basis for Hol 1 (Σ g ), such that a j ζ k = δ jk, and Π is the matrix with entries b j ζ k. Jacobian variety J (Σ g ) = C g /span of columns of (I g, Π). Riemann s theta series: θ(z) = e 2πi[1 2 n Πn+n z]. n Z g (where x y = x T y = x 1 y 1 + x 2 y x n y n.)

14 Riemann surface ζ 1, ζ 2,..., ζ g basis for Hol 1 (Σ g ), such that a ζ j k = δ jk, and Π is the matrix with entries b ζ j k. Jacobian variety J (Σ g ) = C g /span of columns of (I g, Π). Riemann s theta series: θ µ (z) = 2( µ N +n ) Π( µ N +n )+( µ N +n ) z] g, µ Z n Z g e 2πi[1 (where x y = x T y = x 1 y 1 + x 2 y x n y n.) N.

15 Classical theta functions

16 There are two group actions on the space of theta functions

17 There are two group actions on the space of theta functions one that arises from the symmetries of the Riemann surface Carl G.J. Jacobi

18 There are two group actions on the space of theta functions one that arises from the symmetries of the Riemann surface Carl G.J. Jacobi and one that arises from the group law on the Jacobian torus André Weil

19 There is a quantum mechanical model (see e.g. which Y. Manin) in

20 There is a quantum mechanical model (see e.g. which Y. Manin) in theta functions are states (aka wave functions, they are vectors in the Hilbert space of the quantization)

21 There is a quantum mechanical model (see e.g. which Y. Manin) in theta functions are states the second group action arises from the quantization of exponentials on the Jacobian variety (the quantized exponentials are linear operators on the Hilbert space)

22 There is a quantum mechanical model (see e.g. which Y. Manin) in theta functions are states the second group action arises from the quantization of exponentials on the Jacobian variety the first group action arises from the quantization of changes of coordinates.

23 There is a quantum mechanical model (see e.g. which Y. Manin) in theta functions are states the second group action arises from the quantization of exponentials on the Jacobian variety the first group action arises from the quantization of changes of coordinates. This is similar to the quantization of several free particles (the Schrödinger representation and the metaplectic representation). It arises from quantizing g one-dimensional particles with periodic positions and momenta.

24 There is a quantum mechanical model (see e.g. which Y. Manin) in theta functions are states the second group action arises from the quantization of exponentials on the Jacobian variety the first group action arises from the quantization of changes of coordinates. Planck s constant is N 1, N even integer. The classical phase space is the Jacobian variety associated to a genus g surface (which is a 2g-dimensional torus).

25 States: linear combinations of θ µ (z) = 2( µ N +n )Π( µ N +n )+( µ N +n )z] g, µ Z n Z g e 2πiN[1 Operators: quantized exponentials Op (e 2πi(px+qy)) θ µ = e πi N pq 2πi N µq θ µ+p. N.

26 States - obtained via geometric quantization: θ µ (z) = 2( µ N +n )Π( µ N +n )+( µ N +n )z] g, µ Z n Z g e 2πiN[1 Operators - obtained via Weyl quantization: Op (e 2πi(px+qy)) θ µ = e πi N pq 2πi N µq θ µ+p. N.

27 States: θ µ (z) = Operators: n Z g e 2πiN[1 Op 2( µ N +n )Π( µ N +n )+( µ N +n )z], µ Z g (e 2πi(px+qy)) θ µ = e πi N pq 2πi N µq θ µ+p. N. Op (e 2πi(px+qy)+πi N k) θ µ = e πi N pq 2πi N µq+πi N k θ µ+p. This is the action of a finite Heisenberg group.

28 The finite Heisenberg group, which we denote by H(Z g N ), is a quotient of {(p, q, k) p, q Z g, k Z} (p, q, k)(p, q, k ) = (p + p, q + q, k + k + pq qp )

29 The finite Heisenberg group, which we denote by H(Z g N ), is a quotient of {(p, q, k) p, q Z g, k Z} (p, q, k)(p, q, k ) = (p + p, q + q, k + k + pq qp ) Theorem ( Stone-von Neumann ) The representation of H(Z g N ) on theta functions is the unique unitary irreducible representation of this group in which (0, 0, k) acts as multiplication by e πi N k.

30 The finite Heisenberg group, which we denote by H(Z g N ), is a quotient of {(p, q, k) p, q Z g, k Z} (p, q, k)(p, q, k ) = (p + p, q + q, k + k + pq qp ) Theorem ( Stone-von Neumann ) The representation of H(Z g N ) on theta functions is the unique unitary irreducible representation of this group in which (0, 0, k) acts as multiplication by e πi N k. Corollary Each homeomorphism of the Riemann surface induces a unitary map on theta functions. This gives rise to the action of the modular group on theta functions.

31 Theorem ( Stone-von Neumann ) The representation of H(Z g N ) on theta functions is the unique unitary irreducible representation of this group in which (0, 0, k) acts as multiplication by e πi N k. Observation (G.-Uribe): This theorem implies that all the information about the action of the quantized exponentials and the action of the mapping class group of the surface is contained in H(Z g N ).

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33 exponentials on the Jacobian elements of the first homology group of the surface curves on the Riemann surface

34 exponentials on the Jacobian elements of the first homology group of the surface curves on the Riemann surface The group of exponential functions on the Jacobian variety is isomorphic to the first homology group of the Riemann surface, e 2πi(px+qy) (p, q) Z 2g = H 1 (Σ g, Z), where the equality Z 2g = H 1 (Σ g, Z) is realized using the cannonical basis on which periods are computed.

35 exponentials on the Jacobian elements of the first homology group of the surface curves on the Riemann surface The group of exponential functions on the Jacobian variety is isomorphic to the first homology group of the Riemann surface, e 2πi(px+qy) (p, q) Z 2g = H 1 (Σ g, Z), where the equality Z 2g = H 1 (Σ g, Z) is realized using the cannonical basis on which periods are computed.

36 exponentials on the Jacobian elements of the first homology group of the surface curves on the Riemann surface The group of exponential functions on the Jacobian variety is isomorphic to the first homology group of the Riemann surface, e 2πi(px+qy) (p, q) Z 2g = H 1 (Σ g, Z), where the equality Z 2g = H 1 (Σ g, Z) is realized using the cannonical basis on which periods are computed.

37 exponentials on the Jacobian elements of the first homology group of the surface curves on the Riemann surface The group of exponential functions on the Jacobian variety is isomorphic to the first homology group of the Riemann surface, e 2πi(px+qy) (p, q) Z 2g = H 1 (Σ g, Z), where the equality Z 2g = H 1 (Σ g, Z) is realized using the cannonical basis on which periods are computed.

38 Multiplication in the Heisenberg group

39 Multiplication in the Heisenberg group Op ( e 2πix) Op (e 2πiy) = e πi ( N Op e 2πi(x+y)).

40 Multiplication in the Heisenberg group Op ( e 2πix) Op (e 2πiy) = e πi ( N Op e 2πi(x+y)). So the Heisenberg group is a group of curves!

41 The representation of the Heisenberg group H(Z g 2N ) on theta functions arises as an induced representation.

42 The representation of the Heisenberg group H(Z g 2N ) on theta functions arises as an induced representation. Extend the character χ : {(0, 0, k) k Z 2N } C, to a maximal abelian subgroup of H(Z g 2N ). χ((0, 0, k)) = e πi N k

43 The representation of the Heisenberg group H(Z g 2N ) on theta functions arises as an induced representation. Extend the character χ : {(0, 0, k) k Z 2N } C, χ((0, 0, k)) = e πi N k to a maximal abelian subgroup of H(Z g 2N ). Example: the subgroup with elements of the form (0, q, k).

44 The representation of the Heisenberg group H(Z g 2N ) on theta functions arises as an induced representation. Extend the character χ : {(0, 0, k) k Z 2N } C, χ((0, 0, k)) = e πi N k to a maximal abelian subgroup of H(Z g 2N ). The representation induced by χ is the left regular action of the Heisenberg group on a quotient of its group algebra by relations of the form uu χ(u ) 1 u = 0, for u in the maximal abelian subgroup.

45 The representation of the Heisenberg group H(Z g 2N ) on theta functions arises as an induced representation. H(Z g 2N ): group of curves C[H(Zg 2N )]: algebra of curves space of theta functions as a quotient of C[H(Z g 2N )] obtained by filling the inside of the surface.

46 The representation of the Heisenberg group H(Z g 2N ) on theta functions arises as an induced representation. H(Z g 2N ): group of curves C[H(Zg 2N )]: algebra of curves space of theta functions as a quotient of C[H(Z g 2N )] obtained by filling the inside of the surface. We need to add framing to the curves!

47 The representation of the Heisenberg group H(Z g 2N ) on theta functions arises as an induced representation. group of curves algebra of curves fill the inside of the surface The theta functions θ Π µ (z) are

48 The representation of the Heisenberg group H(Z g 2N ) on theta functions arises as an induced representation. group of curves algebra of curves fill the inside of the surface The theta functions θ Π µ (z) are The space of theta functions is a skein module of the handlebody.

49 The representation of the Heisenberg group on theta functions arises as an induced representation. group of curves algebra of curves fill the inside of the surface The theta functions θµ Π (z) are The space of theta functions is a skein module of the handlebody. The notion of a skein module was introduced by J. Przytycki: Factor the space of framed links by skein relations.

50 The representation of the Heisenberg group on theta functions arises as an induced representation. group of curves algebra of curves fill the inside of the surface The theta functions θµ Π (z) are The space of theta functions is a skein module of the handlebody. Factor the vector space with basis the framed links inside the handlebody by the skein relations:

51 The action of the mapping class group If h is a homeomorphism of the surface, then h acts linearly on the first homology group, and so it acts on exponentials. Because of the Stone-von Neumann theorem there exists an automorphism on the space of theta functions, F(h), such that Op(h f) = F(h) 1 Op(f)F(h).

52 The action of the mapping class group If h is a homeomorphism of the surface, then h acts linearly on the first homology group, and so it acts on exponentials. Because of the Stone-von Neumann theorem there exists an automorphism on the space of theta functions, F(h), such that Op(h f) = F(h) 1 Op(f)F(h). The map F(h) is a discrete Fourier transform. The above equation is known in the theory of pseudo-differential operators as an exact Egorov identity.

53 The action of the mapping class group If h is a homeomorphism of the surface, then h acts linearly on the first homology group, and so it acts on exponentials. Because of the Stone-von Neumann theorem there exists an automorphism on the space of theta functions, F(h), such that Op(h f) = F(h) 1 Op(f)F(h). This can be translated into topological language, and interpreted in terms of handle slides in dimension 4.

54 Handleslide in dimension 3 for 1-handles:

55 Handleslide in dimension 3 for 1-handles: Attaching a 2-handle to a 3-ball:

56 Handleslide in dimension 3 for 1-handles: Handleslide in dimension 3 for 2-handles:

57 Handleslide in dimension 3 for 1-handles: Handleslide in dimension 3 for 2-handles:

58 Every 3-dimensional manifold can be obtained as the boundary of a 4-dimensional handlebody obtained by attaching 2-handles to a 4-dimensional ball. Handleslides Kirby calculus

59 Every 3-dimensional manifold can be obtained as the boundary of a 4-dimensional handlebody obtained by attaching 2-handles to a 4-dimensional ball. Handleslides Kirby calculus This yields the 3-manifold invariants and the topological quantum field theory of abelian Chern-Simons theory. Theorem. (G.-Hamilton) There is a UNIQUE topological quantum field theory that unifies, for Riemann surfaces of all genera, the spaces of theta functions, and the actions of finite Heisenberg groups and modular groups.

60 Finite Heisenberg group 2D Theta functions 3D Discrete Fourier transforms 4D

61 Finite Heisenberg group 2D Theta functions 3D Discrete Fourier transforms 4D

62 Finite Heisenberg group 2D Theta functions 3D Discrete Fourier transforms 4D

63 Finite Heisenberg group 2D Theta functions 3D Discrete Fourier transforms 4D With Hamilton and Uribe we were able to recover the main constructs of Edward Witten s abelian Chern-Simons theory.

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67 Knot diagrams have a symmetry, called the third Reidemeister move.

68 Knot diagrams have a symmetry, called the third Reidemeister move.

69 Knot diagrams have a symmetry, called the third Reidemeister move.

70 Knot diagrams have a symmetry, called the third Reidemeister move.

71 Knot diagrams have a symmetry, called the third Reidemeister move. This has been related to the Bethe Ansatz and the Yang-Baxter equation in statistical physics.

72 Knot diagrams have a symmetry, called the third Reidemeister move. This has been related to the Bethe Ansatz and the Yang-Baxter equation in statistical physics.

73 Vladimir Drinfeld related this symmetry to quantum groups.

74 Vladimir Drinfeld related this symmetry to quantum groups. So there is a quantum group that models the space of theta functions, the action of the finite Heisenberg group, and of the modular group.

75 Vladimir Drinfeld related this symmetry to quantum groups. So there is a quantum group that models the space of theta functions, the action of the finite Heisenberg group, and of the modular group. This quantum group is associated to U(1).

76 The quantum group associated to theta functions is the Hopf algebra C[Z 2N ] = C[K]/K 2N = 1, with comultiplication, counit and antipode defined by (K j ) = K j K j, ɛ(k j ) = 1, S(K j ) = K 2N j.

77 The quantum group associated to theta functions is the Hopf algebra C[Z 2N ] = C[K]/K 2N = 1, with comultiplication, counit and antipode defined by (K j ) = K j K j, ɛ(k j ) = 1, S(K j ) = K 2N j. This quantum group was first introduced by Murakami, Ohtsuki, Okada to model their 3-manifold invariant.

78 The quantum group associated to theta functions is the Hopf algebra C[Z 2N ] = C[K]/K 2N = 1, with comultiplication, counit and antipode defined by (K j ) = K j K j, ɛ(k j ) = 1, S(K j ) = K 2N j. This quantum group was first introduced by Murakami, Ohtsuki, Okada to model their 3-manifold invariant. The irreducible representations of this quantum group are V j, j = 0, 1,..., 2N 1, K v = e πi N v.

79 The quantum group associated to theta functions is the Hopf algebra C[Z 2N ] = C[K]/K 2N = 1, with comultiplication, counit and antipode defined by (K j ) = K j K j, ɛ(k j ) = 1, S(K j ) = K 2N j. This quantum group was first introduced by Murakami, Ohtsuki, Okada to model their 3-manifold invariant. The irreducible representations of this quantum group are V j, j = 0, 1,..., 2N 1, K v = e πi N v. This quantum group is NOT a modular Hopf algebra!

80 Theta functions are knots and links inside the handlebody colored by representations of this quantum group.

81 Theta functions are knots and links inside the handlebody colored by representations of this quantum group. The Heisenberg group is represented by curves on the boundary colored by irreducible representations.

82 Theta functions are knots and links inside the handlebody colored by representations of this quantum group. The Heisenberg group is represented by curves on the boundary colored by irreducible representations. The discrete Fourier transforms of the action of the modular group are represented by certain curves on the boundary colored by elements of the representation ring of the quantum group.

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