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628
Lectures on 2D YangMills Theory, Equivariant Cohomology and Topological Field Theories
, 1996
"... These are expository lectures reviewing (1) recent developments in twodimensional YangMills theory and (2) the construction of topological field theory Lagrangians. Topological field theory is discussed from the point of view of infinitedimensional differential geometry. We emphasize the unifying ..."
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Cited by 141 (11 self)
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These are expository lectures reviewing (1) recent developments in twodimensional YangMills theory and (2) the construction of topological field theory Lagrangians. Topological field theory is discussed from the point of view of infinitedimensional differential geometry. We emphasize the unifying role of equivariant cohomology both as the underlying principle in the formulation of BRST transformation laws and as a central concept in the geometrical interpretation of topological field theory path integrals.
New Publickey Cryptosystem Using Braid Groups
 Advances in cryptology—CRYPTO 2000 (Santa Barbara, CA), 166–183, Lecture Notes in Comput. Sci. 1880
, 2000
"... Abstract. The braid groups are infinite noncommutative groups naturally arising from geometric braids. The aim of this article is twofold. One is to show that the braid groups can serve as a good source to enrich cryptography. The feature that makes the braid groups useful to cryptography includes ..."
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Cited by 125 (4 self)
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Abstract. The braid groups are infinite noncommutative groups naturally arising from geometric braids. The aim of this article is twofold. One is to show that the braid groups can serve as a good source to enrich cryptography. The feature that makes the braid groups useful to cryptography includes the followings: (i) The word problem is solved via a fast algorithm which computes the canonical form which can be efficiently manipulated by computers. (ii) The group operations can be performed efficiently. (iii) The braid groups have many mathematically hard problems that can be utilized to design cryptographic primitives. The other is to propose and implement a new key agreement scheme and public key cryptosystem based on these primitives in the braid groups. The efficiency of our systems is demonstrated by their speed and information rate. The security of our systems is based on topological, combinatorial and grouptheoretical problems that are intractible according to our current mathematical knowledge. The foundation of our systems is quite different from widely used cryptosystems based on number theory, but there are some similarities in design. Key words: public key cryptosystem, braid group, conjugacy problem, key exchange, hard problem, noncommutative group, oneway function, public key infrastructure 1
Braid Groups are Linear
 J. Amer. Math. Soc
, 2001
"... The braid group Bn can be dened as the mapping class group of the npunctured disk. A group is said to be linear if it admits a faithful representation into a group of matrices over R. Recently Daan Krammer has shown that a certain representation of the braid groups is faithful for the case n = ..."
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Cited by 120 (7 self)
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The braid group Bn can be dened as the mapping class group of the npunctured disk. A group is said to be linear if it admits a faithful representation into a group of matrices over R. Recently Daan Krammer has shown that a certain representation of the braid groups is faithful for the case n = 4. In this paper, we show that it is faithful for all n. 1.
Infinitesimal presentations of the Torelli groups
 Ha2] [HL] [KM] [Jo83
, 1997
"... 2. Braid groups in positive genus 601 3. Relative completion of mapping class groups 603 4. Mixed Hodge structures on Torelli groups 608 ..."
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Cited by 95 (14 self)
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2. Braid groups in positive genus 601 3. Relative completion of mapping class groups 603 4. Mixed Hodge structures on Torelli groups 608
The computational Complexity of Knot and Link Problems
 J. ACM
, 1999
"... We consider the problem of deciding whether a polygonal knot in 3dimensional Euclidean space is unknotted, capable of being continuously deformed without selfintersection so that it lies in a plane. We show that this problem, unknotting problem is in NP. We also consider the problem, unknotting pr ..."
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Cited by 78 (9 self)
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We consider the problem of deciding whether a polygonal knot in 3dimensional Euclidean space is unknotted, capable of being continuously deformed without selfintersection so that it lies in a plane. We show that this problem, unknotting problem is in NP. We also consider the problem, unknotting problem of determining whether two or more such polygons can be split, or continuously deformed without selfintersection so that they occupy both sides of a plane without intersecting it. We show that it also is in NP. Finally, we show that the problem of determining the genus of a polygonal knot (a generalization of the problem of determining whether it is unknotted) is in PSPACE. We also give exponential worstcase running time bounds for deterministic algorithms to solve each of these problems. These algorithms are based on the use of normal surfaces and decision procedures due to W. Haken, with recent extensions by W. Jaco and J. L. Tollefson.
Higherdimensional algebra VI: Lie 2algebras,
, 2004
"... The theory of Lie algebras can be categorified starting from a new notion of ‘2vector space’, which we define as an internal category in Vect. There is a 2category 2Vect having these 2vector spaces as objects, ‘linear functors’ as morphisms and ‘linear natural transformations ’ as 2morphisms. We ..."
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Cited by 77 (15 self)
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The theory of Lie algebras can be categorified starting from a new notion of ‘2vector space’, which we define as an internal category in Vect. There is a 2category 2Vect having these 2vector spaces as objects, ‘linear functors’ as morphisms and ‘linear natural transformations ’ as 2morphisms. We define a ‘semistrict Lie 2algebra ’ to be a 2vector space L equipped with a skewsymmetric bilinear functor [·, ·]: L × L → L satisfying the Jacobi identity up to a completely antisymmetric trilinear natural transformation called the ‘Jacobiator’, which in turn must satisfy a certain law of its own. This law is closely related to the Zamolodchikov tetrahedron equation, and indeed we prove that any semistrict Lie 2algebra gives a solution of this equation, just as any Lie algebra gives a solution of the Yang–Baxter equation. We construct a 2category of semistrict Lie 2algebras and prove that it is 2equivalent to the 2category of 2term L∞algebras in the sense of Stasheff. We also study strict and skeletal Lie 2algebras, obtaining the former from strict Lie 2groups and using the latter to classify Lie 2algebras in terms of 3rd cohomology classes in Lie algebra cohomology. This classification allows us to construct for any finitedimensional Lie algebra g a canonical 1parameter family of Lie 2algebras g � which reduces to g at � = 0. These are closely related to the 2groups G � constructed in a companion paper.
Compact Stein surfaces with boundary as branched covers of B4
, 2000
"... We prove that Stein surfaces with boundary coincide up to orientation preserving diffeomorphisms with simple branched coverings of B 4 whose branch set is a positive braided surface. As a consequence, we have that a smooth oriented 3manifold is Stein fillable iff it has a positive openbook decompo ..."
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Cited by 73 (6 self)
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We prove that Stein surfaces with boundary coincide up to orientation preserving diffeomorphisms with simple branched coverings of B 4 whose branch set is a positive braided surface. As a consequence, we have that a smooth oriented 3manifold is Stein fillable iff it has a positive openbook decomposition.
Vassiliev Homotopy String Link Invariants
, 1995
"... . We investigate Vassiliev homotopy invariants of string links, and nd that in this particular case, most of the questions left unanswered in [3] can be answered armatively. In particular, Vassiliev invariants classify string links up to homotopy, and all Vassiliev homotopy string link invariants co ..."
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Cited by 62 (4 self)
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. We investigate Vassiliev homotopy invariants of string links, and nd that in this particular case, most of the questions left unanswered in [3] can be answered armatively. In particular, Vassiliev invariants classify string links up to homotopy, and all Vassiliev homotopy string link invariants come from marked surfaces as in [3], using the same construction that in the case of knots gives the HOMFLY and Kauman polynomials. Alongside, the Milnor invariants of string links are shown to be Vassiliev invariants, and it is reproven, by elementary means, that Vassiliev invariants classify braids. Contents 1. Introduction 1 2. Vassiliev invariants of string links 3 2.1. A brief review of [3] 3 2.2. Vassiliev invariants of string links 4 3. Vassiliev homotopy string link invariants 5 4. Vassiliev invariants classify braids 9 4.1. Braids 9 4.2. Braids with double points 11 5. On the Milnor invariants 13 5.1. Vassiliev invariants classify string links up to homotopy 13 5.2. The Milnor ...