Search results for "Solvable models"
showing 3 items of 3 documents
Conformal and non-conformal symmetries in 2D dilaton gravity
1996
We introduce new extra symmetry transformations for generic 2D dilaton-gravity models. These symmetries are non-conformal but special linear combinations of them turn out to be the extra (conformal) symmetries of the CGHS model and the model with an exponential potential. We show that one of the non-conformal extra symmetries can be converted into a conformal one by means of adequate field redefinitions involving the metric and the derivatives of the dilaton. Finally, by expressing the Polyakov-Liouville effective action in terms of an auxiliary invariant metric, we construct one-loop models which maintain the extra symmetry of the classical action. © 1997 Elsevier Science B.V.
Superradiant Quantum Phase Transition for an Exactly Solvable Two-Qubit Spin-Boson Model
2023
A spin-boson-like model with two interacting qubits is analysed. The model turns out to be exactly solvable since it is characterized by the exchange symmetry between the two spins. The explicit expressions of eigenstates and eigenenergies make it possible to analytically unveil the occurrence of first-order quantum phase transitions. The latter are physically relevant since they are characterized by abrupt changes in the two-spin subsystem concurrence, in the net spin magnetization and in the mean photon number.