|  Approaches to Quantum Field Theory | 
Canonical Quantization > s.a. canonical quantum mechanics
  [including group quantization]; geometric quantization.
  * Idea: Choose a
    Hilbert space of states \(\cal H\) which carries a representation of
    an algebra of observables; The fields are operator-valued distributions,
    that have to be smeared in order to give well-defined predictions.
  * Schrödinger picture:
    States are functionals on the quantum configuration space, which is not the
    classical one of C2 functions on a spacelike
    hypersurface but, e.g., for scalar fields, the space of tempered distributions.
  * Caveat: Evolution cannot
    be unitarily implemented between arbitrary curved Cauchy surfaces!
  * Operators: In order to be
    well-defined, the usual field operators must be smeared with 3D distributions.
  @ Schrödinger picture:
    Stoyanovsky in(04)mp/02 [Schrödinger equation as variational differential equation];
    Corichi et al CQG(03)gq/02 [curved spacetime ambiguities];
    Solomon qp/03 [vs Heisenberg];
    Stoyanovsky a1008;
    > s.a. representations of quantum mechanics.
  @ Arbitrary spacelike slices: Torre & Varadarajan PRD(98)ht/97,
    CQG(99)ht/98;
    Helfer ht/99,
    ht/99.
  @ Covariant, based on de Donder-Weyl:
    Nikolić EPJC(05)ht/04;
    von Hippel & Wohlfarth EPJC(06)ht/05.
  @ Choice of representation: Ashtekar & Isham PLB(92) [inequivalent algebras];
    Florig & Summers PLMS(00);
    Czachor & Wilczewski IJTP(07)qp/05 [and experiment].
  @ Precanonical quantization: Kanatchikov ATMP-a1112,
    ATMP-a1312 [and the Schrödinger wave functional];
    > s.a. approaches to quantum gravity.
  @ General-boundary formulation: Oeckl PRD(06)ht/05;
    Oeckl Sigma(12)-a1009 [holomorphic quantization, linear field theory];
    Colosi & Dohse JGP(17)-a1011 [S-matrix, curved spacetimes];
    Oeckl JGP(12)-a1104 [affine holomorphic quantization];
    Oeckl ATMP(15)-a1201 [Schrödinger-Feynman quantization],
    AIP(12)-a1210 [reverse-engineering quantum field theory];
    Banisch et al CQG(13)-a1310 [Unruh-DeWitt detector and vacuum];
    Colosi & Oeckl a2009 [fully local description];
    Colosi & Oeckl a2104 [quantization of the evanescent sector];
    > s.a. quantization of gauge theories;
      klein-gordon fields in AdS spacetime.
  @ Light-front quantization: 
    Collins a1801 [non-triviality of the vacuum];
    Mannheim et al a2005,
    Polyzou a2102
      [comparison with instant-time quantization].
  @ Variations, generalizations: Rayner CQG(90) [loop-based, gravity and scalar field];
    Solovyov et al ht/04 [loop-based];
    Manrique et al CQG(06)
      [loop quantization and 2D Ising field theory];
    Adorno & Klauder IJMPA(14)-a1403 [enhanced quantization, for bosons, fermions, and anyons].
  @ Related topics: Banai JMP(87);
    Danos ht/97 [particles and systems].
  > Specific theories:
    see canonical quantum gravity; klein-gordon fields;
    types of quantum fields [including affine quantization, polymer variables].
  > Related topics:
    see fock space; green
    functions; symplectic structures in physics,
    and types.
Covariant Quantization
  > s.a. klein-gordon fields; quantum gravity.
  * Steps: Define
    pure frequency solutions, 1-particle Hilbert space, creation and
    annihilation operators, full Hilbert space with Fock structure.
  * Bosons: The commutation
    relations between annihilation and creation operators are [a(f),
    a*(g)] = (f | g), [a(f),
    a(g)] = 0; The a(f)s are unbounded (this
    can be seen from the commutation relations), and one has to generate the
    algebra using exp[i (α a + α*a*)].
  * Fermions: The
    annihilation and creation operators satisfy the anticommutation relations
    {a(f), a*(g)} = (f | g),
    {a(f), a(g)} = 0; The a(f)s
    are bounded.
Other Approaches
  > s.a. algebraic and axiomatic; formalism and techniques
  [including non-perturbative approach]; perturbative approach.
  @ Relationships: Teleki & Noga ht/06 [operator and path integral].
  @ Phase space approach: Zachos & Curtright PTPS(99)ht-conf.
  @ Without infinities / renormalization: Takook IJMPE(05)gq/00 [λφ4];
    Stefanovich AP(01);
    Biswas ht/05 [composite particles];
    Wang ChPC(11)-a1006 [extended particles];
    Klauder MPLA(12)-a1112 [curing the mutually-singular-measures problem];
    Czachor a1209;
    Teufel & Tumulka a1505 [Hamiltonians with new boundary conditions];
    Galvan a1607 [interaction Laplacian method];
    Prabhu a1905
      [using statistical mechanics, finite vacuum energy density].
  @ Classical non-local model:
    Morgan qp/01 [for Klein-Gordon],
    qp/01 [for electromagnetism].
  @ Other approaches:
    Czachor qp/99 [single oscillator];
    Brodsky FdP(02)ht/01 [Heisenberg matrix formulation];
    Gurău et al AHP(09)-a0807 [based on marked trees];
    Stoyanovsky in(07)-a0901;
    Floerchinger a1004 [as a bilocal statistical field theory];
    Johnson a1203;
    Anselmi EPJC(13)-a1205 [general field-covariant approach, and renormalization];
    Sulis a1502 [process algebra approach];
    Tilloy a1702
      [as a Lorentz invariant statistical field theory];
    Sorkin IJGMP(17)-a1703 [based on the Wightman function];
    > s.a. Fermionic Projector.
  @ World-line approach: Rylov ht/01;
    Gies & Hämmerling PRD(05) [spin-gauge field coupling, QED].
  @ PT-symmetric scalar field theory:
    Shalaby & Al-Thoyaib PRD(10)-a0901 [and the cosmological constant];
    Bender et PRD(12)-a1201.
  @ Generalizations: Yurtsever CQG(94)gq/93 [quantum field theory on a topology, and small-scale structure];
    > s.a. generalized quantum field theories.
  > Related topics: see
    Hopf Algebra; path integrals;
    quantum field theory [conceptual]; quantum fields in
    curved spacetime; stochastic quantization.
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