Light-front Ward-Takahashi identity for two-fermion systems
- Departamento de Fisica, Instituto Tecnologico de Aeronautica, 12.228-900 Sao Jose dos Campos, Sao Paulo (Brazil)
- Dipartimento di Fisica, Universita di Roma 'Tor Vergata' and Istituto Nazionale di Fisica Nucleare, Sezione Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione Roma I, Piazzale A. Moro 2, I-00185 Roma (Italy)
- Institute for Theoretical Physics, Leibniz University, D-30167 Hannover (Germany)
We propose a three-dimensional electromagnetic current operator within light-front dynamics that satisfies a light-front Ward-Takahashi identity for two-fermion systems. The light-front current operator is obtained by a quasipotential reduction of the four-dimensional current operator and acts on the light-front valence component of bound or scattering states. A relation between the light-front valence wave function and the four-dimensional Bethe-Salpeter amplitude both for bound or scattering states is also derived, such that the matrix elements of the four-dimensional current operator can be fully recovered from the corresponding light-front ones. The light-front current operator can be perturbatively calculated through a quasipotential expansion, and the divergence of the proposed current satisfies a Ward-Takahashi identity at any given order of the expansion. In the quasipotential expansion the instantaneous terms of the fermion propagator are accounted for by the effective interaction and two-body currents. We exemplify our theoretical construction in the Yukawa model in the ladder approximation, investigating in detail the current operator at the lowest nontrivial order of the quasipotential expansion of the Bethe-Salpeter equation. The explicit realization of the light-front form of the Ward-Takahashi identity is verified. We also show the relevance of instantaneous terms and of the pair contribution to the two-body current and the Ward-Takahashi identity.
- OSTI ID:
- 21205134
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 77, Issue 11; Other Information: DOI: 10.1103/PhysRevD.77.116010; (c) 2008 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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