|  Integrable Systems | 
In General > s.a. integrable
  quantum systems; types of integrable systems.
  * Idea: (Liouville) A system
    with n degrees of freedom is integrable if it has n conserved
    quantities in involution (commuting); Then in principle the Hamilton equations
    can be reduced to quadratures.
  * Lax pair / equation: An
    integrable Hamiltonian system has an associated Lax pair of matrices
    S and U, satisfying the equation dS/dt
    = [S,U], equivalent to the dynamical equations for the
    system; As a consequence, the quantities
    Ik:=
    k−1
    tr S k
    are a sequence of invariants of the system.
  * Relationships: The non-linear
    equations of motion / field equations are the integrability conditions for
    systems of linear differential equations with a spectral parameter.
  * Conserved quantities:
    If the system is in the form H = gab
    pa pb
    and ka is a Killing vector field of
    gab, I1
    = ka pa;
    If kab is a Killing tensor, ...
Special Concepts and Techniques
  @ General references: Haak JMP(94) [symmetries, generalized Bäcklund transformations];
    Fokas & Gelfand ed-96 [algebraic];
    Mironov ht/96-conf [group theoretic];
    Rasin & Schiff JPA(13) [Gardner method to generate symmetries and conservation laws];
    > s.a. random matrices.
  @ Symmetries: Chavchanidze JPA(04)mp/03 [non-Noether];
    Rastelli a1001
      [on S2, with Platonic symmetries];
    > s.a. symmetries.
  @ Approximating a non-integrable one:
    Kaasalainen & Binney PRL(94).
  @ Relationships between wave equations, AKS theorem:
    Symes PhyD(80).
  @ Related topics: Dullin & Wittek JPA(94) [actions, numerical calculation];
    Bogoyavlenskij CMP(96) [tensor invariants];
    Labrunie & Conte JMP(96) [finding integrals];
    Alvarez et al NPB(98)ht/97 [new approach];
    Fock et al JHEP(00)ht/99 [duality];
    Leach et al JNMP(00)n.SI [from Yang-Baxter];
    Nutku & Pavlov JMP(02)ht/01 [multi-Lagrangians];
    Maciejewski & Przybylska PLA(11) [integrable deformations].
  > Related topics: see harmonic maps;
    KAM Theorem and weak chaos [perturbations];
    Painlevé Analysis; symplectic structures [KdV].
References
  @ General: Das 89,
    & Okubo AP(89),
    & Huang JMP(90);
    Perelomov 90;
    Zakharov ed-91;
    Dorfman 93;
    Frønsdal FP(93);
    Fiorani IJGMP(08)-a0802 [rev, including recent developments];
    Zuparic PhD(09)-a0908 [and quantum];
    Gómez-Ullate et al ed-JPA(10)#43;
    Tudoran JGP(12)-a1106 [unified formulation];
    Doikou IJMPA(12)-a1110 [rev];
    Torrielli JPA-a1606-ln.
  @  Lax equations / pairs:
    Cariñena & Martínez IJMPA(94);
    Rosquist gq/94,
    Rosquist & Goliath GRG(98)gq/97 [tensorial interpretation];
    Baleanu & Baskal MPLA(00)gq/01;
    Przybylska JGP(01) [generalization];
    Sakovich nlin.SI/01 [true and fake];
    Cariglia et al PRD(13)-a1210 [on a curved manifold, geometric formulation].
  @ Geometrical aspects: Pyatov & Solodukhin ed-96;
    Strachan JGP(97)ht/96 [deformed differential calculus];
    Prykarpatsky & Mykytiuk 98 [and Lie-algebraic approach];
    Lesfari JGP(99) [algebraic geometry];
    Grant JGP(01) [Grassmannn structures];
    Clementi & Pettini ap/01;
    Motter & Letelier PRD(02) [coordinate invariance of integrability];
    Cieslinski et al ed-JPA(09) [non-linearity and geometry];
    Ibort & Marmo TMP(12)-a1203.
  @ Space of integrable theories: Mironov & Morozov PLB(02)ht/01 [canonical transformations and flows].
Generalizations
  * Quasi-integrable systems: Classical
    quasi-integrable systems are ones that can be considered ads integrable systems
    with an added non-integrable small perturbation; They have Lyapunov times orders
    of magnitude shorter than their ergodic time, the most clear example being the
    Solar System.
  * Nekhoroshev theorem: An
    n-degree-of-freedom system, with k constants of the motion
    in involution, k ≤ n, has persistent k-dimensional
    invariant tori, and local partial action-angle coordinates, under suitable
    non-degeneracy conditions; Thus, it interpolates between the Poincaré-Lyapunov
    theorem (k = 1) and the Liouville-Arnold theorem (k = n);
    The crucial tool for the proof is a generalization of the Poincaré map.
  @ Partially solvable systems: Gaeta AP(02) [Nekhoroshev theorem];
    Shabat et al ed-04.
  @ Quasi-integrable systems: Ferreira & Zakrzewski JHEP(11)-a1011 [example];
    Goldfriend & Kurchan a1909 [quantum].
  @ Nearly-integrable systems: Fasso & Sansonetto a1601 [almost-symplectic].
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