30 research outputs found
Soliton Spheres
Soliton spheres are immersed 2-spheres in the conformal 4-sphere S^4=HP^1
that allow rational, conformal parametrizations f:CP^1->HP^1 obtained via
twistor projection and dualization from rational curves in CP^{2n+1}. Soliton
spheres can be characterized as the case of equality in the quaternionic
Pluecker estimate. A special class of soliton spheres introduced by Taimanov
are immersions into R^3 with rotationally symmetric Weierstrass potentials that
are related to solitons of the mKdV-equation via the ZS-AKNS linear problem. We
show that Willmore spheres and Bryant spheres with smooth ends are further
examples of soliton spheres. The possible values of the Willmore energy for
soliton spheres in the 3-sphere are proven to be W=4pi*d with d a positive
integer but not 2,3,5, or 7. The same quantization was previously known
individually for each of the three special classes of soliton spheres mentioned
above.Comment: 49 pages, 43 figure
Conformal maps from a 2-torus to the 4-sphere
We study the space of conformal immersions of a 2-torus into the 4-sphere.
The moduli space of generalized Darboux transforms of such an immersed torus
has the structure of a Riemann surface, the spectral curve. This Riemann
surface arises as the zero locus of the determinant of a holomorphic family of
Dirac type operators parameterized over the complexified dual torus. The kernel
line bundle of this family over the spectral curve describes the generalized
Darboux transforms of the conformally immersed torus. If the spectral curve has
finite genus the kernel bundle can be extended to the compactification of the
spectral curve and we obtain a linear 2-torus worth of algebraic curves in
projective 3-space. The original conformal immersion of the 2-torus is
recovered as the orbit under this family of the point at infinity on the
spectral curve projected to the 4-sphere via the twistor fibration.Comment: 27 pages, 5 figure
Constrained Willmore Surfaces
Constrained Willmore surfaces are conformal immersions of Riemann surfaces
that are critical points of the Willmore energy under compactly
supported infinitesimal conformal variations. Examples include all constant
mean curvature surfaces in space forms. In this paper we investigate more
generally the critical points of arbitrary geometric functionals on the space
of immersions under the constraint that the admissible variations
infinitesimally preserve the conformal structure. Besides constrained Willmore
surfaces we discuss in some detail examples of constrained minimal and volume
critical surfaces, the critical points of the area and enclosed volume
functional under the conformal constraint.Comment: 17 pages, 8 figures; v2: Hopf tori added as an example, minor changes
in presentation, numbering changed; v3: new abstract and appendix, several
changes in presentatio
The spectral curve of a quaternionic holomorphic line bundle over a 2-torus
A conformal immersion of a 2-torus into the 4-sphere is characterized by an
auxiliary Riemann surface, its spectral curve. This complex curve encodes the
monodromies of a certain Dirac type operator on a quaternionic line bundle
associated to the immersion. The paper provides a detailed description of the
geometry and asymptotic behavior of the spectral curve. If this curve has
finite genus the Dirichlet energy of a map from a 2-torus to the 2-sphere or
the Willmore energy of an immersion from a 2-torus into the 4-sphere is given
by the residue of a specific meromorphic differential on the curve. Also, the
kernel bundle of the Dirac type operator evaluated over points on the 2-torus
linearizes in the Jacobian of the spectral curve. Those results are presented
in a geometric and self contained manner.Comment: 36 page
Möbius invariante FlĂŒsse von Tori in S4
Diese Arbeit beschreibt, wie BĂ€cklund- und Darbouxtransformationen sowie SolitonenflĂŒsse fĂŒr allgemeine konforme Immersionen von Riemannschen FlĂ€chen in die 4-SphĂ€re definiert werden können. Dabei wird detailliert auf den Zusammenhang zu den klassischen Transformationstheorien fĂŒr Isotherm- und WillmoreflĂ€chen eingegangen, die als SpezialfĂ€lle in der neuen Theorie enthalten sind. Das Hauptinteresse dieser Arbeit gilt den globalen Eigenschaften der Transformationen im Fall konformer Immersionen von Riemannschen FlĂ€chen des Geschlechts 1. Es wird gezeigt, dass im Fall konformer Immersionen eines Torus mit NormalbĂŒndel vom Grad 0 sowohl BĂ€cklund- als auch Darbouxtransformationen das Willmorefunktional und das sogenannte Spektrum erhalten. FĂŒr diese Immersionen wird eine Spektralkurve definiert, welche die Menge der Darbouxtransformationen der Immersion parametrisiert und eine natĂŒrliche Interpretation als holomorphe Kurve in erlaubt. Die SolitonenflĂŒsse werden als spezielle Deformationen quaternionisch projektiver Strukturen eingefĂŒhrt. Es werden Evolutionsgleichungen fĂŒr die Invarianten hergeleitet, die nach dem Fundamentalsatz der FlĂ€chentheorie in der 4--dimensionalen Möbiusgeometrie eine konforme Immersion bis auf Möbiustransformation eindeutig beschreiben. Als Beispiel wird gezeigt, dass der Davey--Stewartson--Fluss fĂŒr FlĂ€chen, im Fall von Zylindern, RotationsflĂ€chen und Kegeln ĂŒber Kurven in 3--dimensionalen Raumformen, den bekannten Rauch--Ring--Fluss fĂŒr Raumkurven ergibt und dass analog der Novikov--Veselov--Fluss dem mKdV--Fluss fĂŒr Raumkurven entspricht. AbschlieĂend werden die beiden folgenden SĂ€tze bewiesen: der erste Satz besagt, dass ein Torus in der 4--SphĂ€re, der in einer 3--SphĂ€re enthalten ist, genau dann unter dem Davey--Stewartson--Fluss stationĂ€r ist, wenn er isotherm und constrained Willmore ist. Der zweite Satz zeigt, dass man den Davey--Stewartson--Fluss unter bestimmten Annahmen als Grenzwert von Darbouxtransformationen erhĂ€lt.This thesis describes, how BĂ€cklund and Darboux transformations as well as soliton flows can be defined for general conformal immersions of Riemann surfaces into the 4-sphere. This generalizes the classical transformation theories fĂŒr isothermic und Willmore surfaces. The emphasis is on the global theory for conformal immersions of tori