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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 31 (1990), S. 757-762 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Conformally invariant nonlinear wave equations in four dimensions, corresponding to multicomponent massless scalar fields with a quartic interaction, are studied. It is proved that the scattering operator S on the space H of finite-Einstein-energy Cauchy data has infinitely many fixed points, as well as periodic points of all orders. There are also Φ∈H such that SnΦ is almost periodic, but not periodic and Φ∈H such that SnΦ is not almost periodic. It is also proved that H admits no conformally invariant Kähler metrics, but infinitely many distinct Kähler metrics invariant under the Poincaré group and scale transformations. Moreover, it is proved that time evolution for these nonlinear wave equations is completely integrable on the space H.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 247-257 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Spin and statistics for topological solitons in nonlinear sigma models are studied using topological methods based on the classical configuration space. Taking as space the connected d-manifold X, and considering nonlinear sigma models with the connected manifold M as target space, topological solitons are given by elements of πd(M). Any topological soliton α∈πd(M) determines a quotient Statn(X,α) of the group of framed braids with n strands on X, such that a framed braid determines a contractible path in the n-soliton sector of the configuration space if and only if its image in Statn(X,α) is the identity. In particular, when M=S2, as in the O(3) nonlinear sigma model with Hopf term, and α∈π2(S2) is a generator, we compute that Statn(R2,α)=Z, while Statn(S2,α)=Z2n. Thus one expects the phase exp(iθ) for interchanging two solitons of type α on S2 to satisfy the constraint θ=kπ/n, k∈Z, when n such solitons are present. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 39 (1998), S. 1251-1271 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We extend ideas developed for the loop representation of quantum gravity to diffeomorphism-invariant gauge theories coupled to fermions. Let P→Σ be a principal G-bundle over space and let F be a vector bundle associated to P whose fiber is a sum of continuous unitary irreducible representations of the compact connected gauge group G, each representation appearing together with its dual. We consider theories whose classical configuration space is A×F, where A is the space of connections on P and F is the space of sections of F, regarded as a collection of Grassmann-valued fermionic fields. We construct the "quantum configuration space" A¯×F¯ as a completion of A×F. Using this, we construct a Hilbert space L2(A¯×F¯) for the quantum theory on which all automorphisms of P act as unitary operators, and determine an explicit "spin network basis" of the subspace L2((A¯×F¯)/G¯) consisting of gauge-invariant states. We represent observables constructed from holonomies of the connection along paths together with fermionic fields and their conjugate momenta as operators on L2((A¯×F¯)/G¯). We also construct a Hilbert space Hdiff of diffeomorphism-invariant states using the group averaging procedure of Ashtekar, Lewandowski, Marolf, Moura˜o and Thiemann. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 6073-6105 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The study of topological quantum field theories increasingly relies upon concepts from higher-dimensional algebra such as n-categories and n-vector spaces. We review progress towards a definition of n-category suited for this purpose, and outline a program in which n-dimensional topological quantum field theories (TQFTs) are to be described as n-category representations. First we describe a "suspension'' operation on n-categories, and hypothesize that the k-fold suspension of a weak n-category stabilizes for k≥n+2. We give evidence for this hypothesis and describe its relation to stable homotopy theory. We then propose a description of n-dimensional unitary extended TQFTs as weak n-functors from the "free stable weak n-category with duals on one object'' to the n-category of "n-Hilbert spaces.'' We conclude by describing n-categorical generalizations of deformation quantization and the quantum double construction. © 1995 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Letters in mathematical physics 38 (1996), S. 129-143 
    ISSN: 1573-0530
    Keywords: 57N13 ; 81T43 ; 83C45 ; topological quantum field theory ; BF theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract Starting from a Lie group G whose Lie algebra is equipped with an invariant nondegenerate symmetric bilinear form, we show that four-dimensional BF theory with cosmological term gives rise to a TQFT satisfying a generalization of Atiyah's axioms to manifolds equipped with principal G-bundle. The case G=GL(4,ℝ) is especially interesting because every 4-manifold is then naturally equipped with a principal G-bundle, namely its frame bundle. In this case, the partition function of a compact oriented 4-manifold is the exponential of its signature, and the resulting TQFT is isomorphic to that constructed by Crane and Yetter using a state sum model, or by Broda using a surgery presentation of four-manifolds.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Letters in mathematical physics 21 (1991), S. 117-121 
    ISSN: 1573-0530
    Keywords: 81E10 ; 81C12 ; 53A30
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract Let ϕ denote the conformally invariant neutral free scalar field on ℝ×S n. The ‘naive’ lightcone Hamiltonian for a ϕp interaction is given by ∭c∶ϕp⋅, where C denotes a lightcone in ℝ×S n, and the Wick power is relative to the free vacuum. We show that this sesquilinear form annihilates the free vacuum if n≥3 is odd, p〉2, and p(n−1)≡0 mod 4.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Letters in mathematical physics 23 (1991), S. 133-141 
    ISSN: 1573-0530
    Keywords: 81R50 ; 16O80 ; 16W30 ; 17B37
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract From a vector spaceV equipped with a Yang-Baxter operatorR one may form the r-symmetric algebraS R V=TV/〈v ⊗w−R(v ⊗w)〉, which is a quantum vector space in the sense of Manin, and the associated quantum matrix algebraM R V=T(End(V))/〈f ⊗g−R(f ⊗g)R -1〉. In the case whenR satisfies a Hecke-type identityR 2=(1−q)R+q, we construct a differential calculus Ω R V forS R V which agrees with that constructed by Pusz, Woronowicz, Wess, and Zumino whenR is essentially theR-matrix of GL q (n). Elements of Ω R V may be regarded as differential forms on the quantum vector spaceS R V. We show that Ω R V isM R V-covariant in the sense that there is a coaction Φ*: Ω R V →M R V ⊗ Ω R V with Φ*d=(1 ⊗ d)Φ* extending the natural coaction Φ:S R V →M R V ⊗S R V.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Letters in mathematical physics 26 (1992), S. 43-51 
    ISSN: 1573-0530
    Keywords: 81T13 ; 57M25 ; 20F36
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract The Vassiliev-Gusarov link invariants of finite type are known to be closely related to perturbation theory for Chern-Simons theory. In order to clarify the perturbative nature of such link invariants, we introduce an algebra V x containing elements g i satisfying the usual braid group relations and elements a i satisfying g i−g infi sup-1 =εa i, where ε is a formal variable that may be regarded as measuring the failure of g infi sup2 to equal 1. Topologically, the elements a i signify intersections. We show that a large class of link invariants of finite type are in one-to-one correspondence with homogeneous Markov traces on V x. We sketch a possible application of link invariants of finite type to a manifestly diffeomorphisminvariant perturbation theory for quantum gravity in the loop representation.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Letters in mathematical physics 31 (1994), S. 205-212 
    ISSN: 1573-0530
    Keywords: 58F08 ; 70H35
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract Using basic ideas from algebraic geometry, we extend the methods of Lagrangian and symplectic mechanics to treat a large class of discrete mechanical systems, that is, systems such as cellular automata in which time proceeds in integer steps and the configuration space is discrete. In particular, we derive an analog of the Euler-Lagrange equation from a variational principle, and prove an analog of Noether's theorem. We also construct a symplectic structure on the analog of the phase space, and prove that it is preserved by time evolution.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Letters in mathematical physics 31 (1994), S. 213-223 
    ISSN: 1573-0530
    Keywords: 81T13 ; 83C45 ; 81S40 ; 81T08
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract LetP →M be a principalG-bundle. We construct well-defined analogs of Lebesgue measure on the spaceA of connections onP and Haar measure on the groupG of gauge transformations. More precisely, we define algebras of ‘cylinder functions’ on the spacesA,G, andA/G, and define generalized measures on these spaces as continuous linear functionals on the corresponding algebras. Borrowing some ideas from lattice gauge theory, we characterize generalized measures onA,G, andA/G in terms of graphs embedded inM. We use this characterization to construct generalized measures onA andG whenG is compact. The ‘uniform’ generalized measure onA is invariant under the group of automorphisms ofP. It projects down to the generalized measure onA/G considered by Ashtekar and Lewandowski in the caseG = SU(n). The ‘generalized Haar measure’ onG is right- and left-invariant as well as Aut(P)-invariant. We show that averaging any generalized measure onA against generalized Haar measure gives aG-invariant generalized measure onA.
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