acta physica slovaca

Acta Physica Slovaca 61, No.2, 129-271 (2011) (142 pages)


Zoltán Bajnok1, Ladislav Šamaj2
    1 Theoretical Physics Research Group, Hungarian Academy of Sciences, Eotvos University, 1117 Budapest, Hungary
    2 Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava, Slovakia

Full text: ::pdf :: (Received 23 May 2011, accepted 24 May 2011)

Abstract: This is the third part of a three-volume introductory course about integrable systems of interacting bodies. The emphasis is put onto the method of Thermodynamic Bethe ansatz. Two kinds of integrable models are studied. Systems of itinerant electrons, forming a part of Condensed Matter Physics, involve the Hubbard lattice model of electrons with short-ranged one-site interactions (Sect. 20) and the s-d exchange Kondo model (Sect. 21), describing the scattering of conduction electrons on a spin-s impurity. Methods and basic concepts used in Quantum Field Theory are explained on the integrable (1 + 1)-dimensional sine-Gordon model. We start with the classical description of the model in Sect. 22, analyze its finite energy field configurations (soliton, anti-soliton and breathers) and show its classical integrability. The model is quantized by using two schemes: the conformal (Sect. 23) and Lagrangian (Sect. 24) quantizations. The scattering matrix of the sine-Gordon theory is derived at the full quantum level in the bootstrap scheme and is compared to its classical limit in Sect. 25. The parameters of the scattering matrix are related to those of the Lagrangian by calculating the ground-state energy in an applied magnetic field in two ways: Conformal perturbation theory and Thermodynamic Bethe ansatz (Sect. 26). The relation of the sine-Gordon theory to the XXZ Heisenberg model, which provides a complete solution of the sine-Gordon model in a finite volume, is pointed out in Sect. 27. The obtained results are applied in Sect. 28. to the derivation of the exact thermodynamics for the (symmetric) two-component Coulomb gas; this is the first classical two-dimensional fluid with exactly solvable thermodynamics.

PACS: 02.30.Ik, 05.30.Fk, 05.30.Jp, 05.50.+q, 75.10.Jm
Keywords: Integrable systems, Scattering matrix, Thermodynamic Bethe ansatz, Hubbard model, Kondo effect, Sine-Gordon model, Conformal quantization, Two-dimensional Coulomb gas.
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