Riemann surfaces. Ian Short. Thursday 29 November 2012

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1 Riemann surfaces Ian Short Thursday 29 November 2012

2 Complex analysis and geometry in the plane

3 Complex differentiability

4 Complex differentiability

5 Complex differentiability

6 Complex differentiability

7 Complex differentiability f (z + w ) = f (z ) + f 0 (z )w + "(w )

8 Complex differentiability f (z + w ) = f (z ) + f 0 (z )w + "(w )

9 Complex differentiability f (z + w ) = f (z ) + f 0 (z )w + "(w )

10 Complex differentiability f (z + w ) = f (z ) + f 0 (z )w + "(w ) Conformal : analytic and bijective

11 Complex differentiability f (z + w ) = f (z ) + f 0 (z )w + "(w ) Conformal : analytic and bijective

12 Complex differentiability f (z + w ) = f (z ) + f 0 (z )w + "(w ) Conformal : analytic and bijective

13 Topologically equivalent domains

14 Topologically equivalent domains

15 Topologically equivalent domains

16 Conformally equivalent domains?

17 Conformally equivalent domains z 7! az + b, ad bc 6= 0 cz + d

18 Riemann mapping theorem

19 Holes and punctures?

20 Holes and punctures?

21 Koebe's theorem

22 Koebe's theorem

23 Koebe's theorem Fixed points, Koebe uniformization and circle packings Zheng-Xu He and Oded Schramm The Annals of Mathematics, 1993

24 The hyperbolic plane

25 The hyperbolic plane (a; b) = inf n R jdz j y o : path from a to b

26 The hyperbolic plane (a; b) = inf n R jdz j y o : path from a to b

27 Quasi-isometric graph

28 Quasi-isometric graph

29 Quasi-isometric graph

30 Disc model of the hyperbolic plane

31 Three geometries

32 Three geometries curvature + 0

33 Three geometries curvature + 0 triangle angles > <

34 Three geometries curvature + 0 triangle angles > < parallel lines 0 1 1

35 Three geometries curvature + 0 triangle angles > < parallel lines circumference 2 sin r 2r 2 sinh r

36 Surfaces

37 Surfaces

38 Surfaces

39 Surfaces

40 Classification of compact surfaces

41 Classification of compact surfaces Conway's ZIP proof George K. Francis & Jerey R. Weeks American Mathematical Monthly, 1999

42 Classification of surfaces

43 Jacob's ladder

44 The infinite Loch Ness monster

45 Riemann surfaces

46 Riemann surfaces

47 Riemann surfaces

48 Riemann surfaces

49 Plane domains

50 The Riemann sphere

51 Analytic maps on Riemann surfaces

52 Analytic maps on Riemann surfaces

53 Analytic maps on Riemann surfaces

54 Analytic maps on Riemann surfaces Conformal : analytic and bijective

55 Lego Riemann surfaces

56 Algebraic curves w 7 = z 3 2z 2 + z

57 Quotient spaces

58 Cylinder G = hz 7! z + 1i

59 Cylinder G = hz 7! z + 1i

60 Cylinder G = hz 7! z + 1i

61 Torus G = hz 7! z + 1; z 7! z + ii

62 Torus G = hz 7! z + 1; z 7! z + ii

63 Torus G = hz 7! z + 1; z 7! z + ii

64 Cylinder G = hz 7! z + 1i

65 Cylinder G = hz 7! z + 1i

66 Cylinder G = hz 7! z + 1i

67 Cylinder G = hz 7! z + 1i

68 Cylinder G = hz 7! 2z i

69 Cylinder G = hz 7! 2z i

70 Cylinder G = hz 7! 2z i

71 Cylinder G = hz 7! 2z i

72 The modular surface G = hz 7! z + 1; z 7! 1 z i

73 The modular surface G = hz 7! z + 1; z 7! 1 z i

74 The modular surface G = hz 7! z + 1; z 7! 1 z i

75 The uniformisation theorem

76 The uniformisation theorem The uniformisation theorem.

77 The uniformisation theorem The uniformisation theorem. Each Riemann surface is conformally equivalent to =G, where is either S, C, or H,

78 The uniformisation theorem The uniformisation theorem. Each Riemann surface is conformally equivalent to =G, where is either S, C, or H, and G is a discrete group of conformal isometries of that acts without xed points.

79 The uniformisation theorem The uniformisation theorem. Each Riemann surface is conformally equivalent to =G, where is either S, C, or H, and G is a discrete group of conformal isometries of that acts without xed points. Further, G is isomorphic to the fundamental group of =G.

80 Spherical Riemann surfaces S=G, where G discrete and has no xed points

81 Euclidean Riemann surfaces C=G, where G discrete and has no xed points

82 Hyperbolic Riemann surfaces

83 Hyperbolic Riemann surfaces

84 Hyperbolic Riemann surfaces Poincaré's theorem. If the sum of each set of equivalent angles is 2, then the group generated by the side pairings is discrete, without xed points, and the polygon is a fundamental region.

85 Geometry of Riemann surfaces

86 Geometry of Riemann surfaces sinh sinh 1

87 Conformal maps

88 Pick's version of Schwarz's lemma

89 Pick's version of Schwarz's lemma S (f (z ); f (w )) R (z ; w )

90 Pick's version of Schwarz's lemma S (f (z ); f (w )) R (z ; w )

91 Group of conformal symmetries

92 Group of conformal symmetries

93 Group of conformal symmetries Conformal symmetry group of R = H=G is N (G)=G

94 Conformal symmetries of compact Riemann surfaces Hurwitz bound. A compact Riemann surface of genus g 2 has no more than 84(g 1) conformal symmetries.

95 Conformal symmetries of compact Riemann surfaces Hurwitz bound. A compact Riemann surface of genus g 2 has no more than 84(g 1) conformal symmetries. Intersting exercise. Prove from the RiemannHurwitz formula that an analytic map from a compact Riemann surface (genus 2) to itself is either constant or a conformal symmetry.

96 Conformal symmetries of multiply connected domains

97 Schwarz reflection principle and Möbius maps

98 Schwarz reflection principle and Möbius maps

99 Schwarz reflection principle and Möbius maps

100 Schwarz reflection principle and Möbius maps

101 Schwarz reflection principle and Möbius maps z 7! az + b cz + d a; b; c; d 2 C ad bc = 1

102 Connectivity 3+

103 Connectivity 3+

104 Connectivity 3+

105 Connectivity 3+ Conformal symmetry group is nite group of Möbius transformations

106 Finite groups of Möbius transformations

107 Finite groups of Möbius transformations

108 Finite groups of Möbius transformations

109 Finite groups of Möbius transformations

110 Finite groups of Möbius transformations

111 Finite groups of Möbius transformations

112 Finite groups of Möbius transformations

113 Finite groups of Möbius transformations

114 Finite groups of Möbius transformations

115 Finite groups of Möbius transformations

116 Finite groups of Möbius transformations

117 Finite groups of Möbius transformations

118 Finite orthogonal groups

119 Finite orthogonal groups

120 Finite orthogonal groups

121 Finite orthogonal groups

122 Finite orthogonal groups

123 Finite orthogonal groups

124 Literature

125 Literature Riemann surfaces, Ahlfors & Sario classic

126 Literature Riemann surfaces, Ahlfors & Sario classic Introduction to Riemann surfaces, Springer old

127 Literature Riemann surfaces, Ahlfors & Sario classic Introduction to Riemann surfaces, Springer old Complex functions, Jones & Singerman good

128 Literature Riemann surfaces, Ahlfors & Sario classic Introduction to Riemann surfaces, Springer old Complex functions, Jones & Singerman good Riemann surfaces, Farkas & Kra hard

129 Literature Riemann surfaces, Ahlfors & Sario classic Introduction to Riemann surfaces, Springer old Complex functions, Jones & Singerman good Riemann surfaces, Farkas & Kra hard Lectures on Riemann surfaces, Forster don't know

130 Literature Riemann surfaces, Ahlfors & Sario classic Introduction to Riemann surfaces, Springer old Complex functions, Jones & Singerman good Riemann surfaces, Farkas & Kra hard Lectures on Riemann surfaces, Forster don't know Algebraic curves and Riemann surfaces, Miranda good

131 Literature Riemann surfaces, Ahlfors & Sario classic Introduction to Riemann surfaces, Springer old Complex functions, Jones & Singerman good Riemann surfaces, Farkas & Kra hard Lectures on Riemann surfaces, Forster don't know Algebraic curves and Riemann surfaces, Miranda good Riemann surfaces, Donaldson new

132 Literature Riemann surfaces, Ahlfors & Sario classic Introduction to Riemann surfaces, Springer old Complex functions, Jones & Singerman good Riemann surfaces, Farkas & Kra hard Lectures on Riemann surfaces, Forster don't know Algebraic curves and Riemann surfaces, Miranda good Riemann surfaces, Donaldson new A primer on Riemann surfaces, Beardon good

133 Literature Riemann surfaces, Ahlfors & Sario classic Introduction to Riemann surfaces, Springer old Complex functions, Jones & Singerman good Riemann surfaces, Farkas & Kra hard Lectures on Riemann surfaces, Forster don't know Algebraic curves and Riemann surfaces, Miranda good Riemann surfaces, Donaldson new A primer on Riemann surfaces, Beardon good Acknowledgements Many ideas due to Alan Beardon.

134 Thank you!

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