A unified approach to the analysis of quantum phase transitions in some
different Curie-Weiss models is proposed such that they are treated and
analyzed under the same general scheme. This approach takes three steps:
balancing the quantum Hamiltonian by an appropriate factor, rewriting the
Hamiltonian in terms of SU(2) operators only, and obtention of a classical
Hamiltonian. SU(2) operators are obtained from creation and annihilation
operators as linear combinations in the case of fermions and as an inverse
Holstein-Primakoff transformation in the case of bosons. This scheme is
successfully applied to Lipkin, pairing, Jaynes-Cummings, bilayer, and
Heisenberg models.Comment: 24 pages, 6 figures, submitted for publication on August 29, 2017
Some errors concerning the Jaynes-Cummings model need to be fixe