Nonlinear Bogolyubov-Valatin transformations: Two modes

• Published in: Annals of physics Vol. 326; no. 11; pp. 2868 - 2933
• Main Authors: Scharnhorst, K., van Holten, J.-W.
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01.11.2011; Elsevier BV
• Subjects: Algebra; ANGULAR MOMENTUM; Canonical transformation; CANONICAL TRANSFORMATIONS; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CLIFFORD ALGEBRA; DIRAC OPERATORS; Equivalence; Fermion; FERMIONS; Group [formula omitted]; HAMILTONIANS; LIE GROUPS; Mathematical analysis; MATHEMATICAL OPERATORS; MATRICES; Matrix methods; Nonlinear Bogolyubov-Valatin transformation; NONLINEAR PROBLEMS; Nonlinear spin transformation; Nonlinearity; PARTICLE PROPERTIES; Physics; QUANTUM OPERATORS; R MATRIX; SPIN; SU GROUPS; SU-4 GROUPS; SUPERSYMMETRY; SYMMETRY; SYMMETRY GROUPS; TENSORS; TRANSFORMATIONS; Group SU; Group S O ( 6 ; R ); Fermion; Clifford algebra; Nonlinear Bogolyubov-Valatin transformation; Canonical transformation; Nonlinear spin transformation
• ISSN: 0003-4916; 1096-035X
• DOI: 10.1016/j.aop.2011.05.001

Extending our earlier study of nonlinear Bogolyubov-Valatin transformations (canonical transformations for fermions) for one fermionic mode, in the present paper, we perform a thorough study of general (nonlinear) canonical transformations for two fermionic modes. We find that the Bogolyubov-Valatin group for n = 2 fermionic modes, which can be implemented by means of unitary SU ( 2 n = 4 ) transformations, is isomorphic to S O ( 6 ; R ) / Z 2 . The investigation touches on a number of subjects. As a novelty from a mathematical point of view, we study the structure of nonlinear basis transformations in a Clifford algebra [specifically, in the Clifford algebra C ( 0 , 4 ) ] entailing (supersymmetric) transformations among multivectors of different grades. A prominent algebraic role in this context is being played by biparavectors (linear combinations of products of Dirac matrices, quadriquaternions, sedenions) and spin bivectors (antisymmetric complex matrices). The studied biparavectors are equivalent to Eddington’s E -numbers and can be understood in terms of the tensor product of two commuting copies of the division algebra of quaternions H . From a physical point of view, we present a method to diagonalize any arbitrary two-fermion Hamiltonians. Relying on Jordan-Wigner transformations for two-spin- 1 2 and single-spin- 3 2 systems, we also study nonlinear spin transformations and the related problem of diagonalizing arbitrary two-spin- 1 2 and single-spin- 3 2 Hamiltonians. Finally, from a calculational point of view, we pay due attention to explicit parametrizations of SU ( 4 ) and S O ( 6 ; R ) matrices (of respective sizes 4×4 and 6×6) and their mutual relation. ► Reveals the structure of nonlinear canonical transformations for two fermionic modes. ► Studies nonlinear basis transformations in a Clifford algebra. ► Focuses on methodological and structural aspects. ► Presents a new approach to the diagonalization of 4×4 matrix Hamiltonians. ► Presents the relation between explicit parametrizations of SU ( 4 ) and S O ( 6 ; R ) matrices.