Supersymmetry in Thermo Field Dynamics

By considering the enlarged thermal system including the heat bath, it is shown that this system has supersymmetry which is not broken at finite temperature. The super algebra is constructed and the Hamiltonian is expressed as the anti-commutator of two kinds of super charges. With this Hamiltonian and the thermal vacuum $\mid 0(\beta)>$, this supersymmetry is found to be preserved.Comment: 12 pages, Latex fil

Noncommutative Thermofield Dynamics

The real-time operator formalism for thermal quantum field theories, thermofield dynamics, is formulated in terms of a path-integral approach in non-commutative spaces. As an application, the two-point function for a thermal non-commutative $\lambda \phi^4$ theory is derived at the one-loop level. The effect of temperature and the non-commutative parameter, competing with one another, is analyzed.Comment: 13 pages; to be published in IJMP-A

Dynamical mapping method in nonrelativistic models of quantum field theory

The solutions of Heisenberg equations and two-particles eigenvalue problems for nonrelativistic models of current-current fermion interaction and $N, \Theta$ model are obtained in the frameworks of dynamical mapping method. The equivalence of different types of dynamical mapping is shown. The connection between renormalization procedure and theory of selfadjoint extensions is elucidated.Comment: 14 page

Finite Temperature Density Matrix Renormalization using an enlarged Hilbert space

We apply a generalization of the time-dependent DMRG to study finite temperature properties of several quantum spin chains, including the frustrated $J_1-J_2$ model. We discuss several practical issues with the method, including use of quantum numbers and finite size effects. We compare with transfer-matrix DMRG, finding that both methods produce excellent results.Comment: 4 pages and 4 figure

QED symmetries in real-time thermal field theory

We study the discrete and gauge symmetries of Quantum Electrodynamics at finite temperature within the real-time formalism. The gauge invariance of the complete generating functional leads to the finite temperature Ward identities. These Ward identities relate the eight vertex functions to the elements of the self-energy matrix. Combining the relations obtained from the $Z_2$ and the gauge symmetries of the theory we find that only one out of eight longitudinal vertex functions is independent. As a consequence of the Ward identities it is shown that some elements of the vertex function are singular when the photon momentum goes to zero.Comment: New version as it will appear in Phys RevD 19 pages, RevTex, 1figur

Action and Hamiltonian for eternal black holes

We present the Hamiltonian, quasilocal energy, and angular momentum for a spacetime region spatially bounded by two timelike surfaces. The results are applied to the particular case of a spacetime representing an eternal black hole. It is shown that in the case when the boundaries are located in two different wedges of the Kruskal diagram, the Hamiltonian is of the form $H = H_+ - H_-$, where $H_+$ and $H_-$ are the Hamiltonian functions for the right and left wedges respectively. The application of the obtained results to the thermofield dynamics description of quantum effects in black holes is briefly discussed.Comment: 24 pages, Revtex, 5 figures (available upon request

Perturbative Quantum Field Theory at Positive Temperatures: An Axiomatic Approach

It is shown that the perturbative expansions of the correlation functions of a relativistic quantum field theory at finite temperature are uniquely determined by the equations of motion and standard axiomatic requirements, including the KMS condition. An explicit expression as a sum over generalized Feynman graphs is derived. The canonical formalism is not used, and the derivation proceeds from the beginning in the thermodynamic limit. No doubling of fields is invoked. An unsolved problem concerning existence of these perturbative expressions is pointed out.Comment: 17pages Late

Scattering in an environment

The cross section of elastic electron-proton scattering taking place in an electron gas is calculated within the Closed Time Path method. It is found to be the sum of two terms, one being the expression in the vacuum except that it involves dressing due to the electron gas. The other term is due to the scattering particles-electron gas entanglement. This term dominates the usual one when the exchange energy is in the vicinity of the Fermi energy. Furthermore it makes the trajectories of the colliding particles more consistent and the collision more irreversible, rendering the scattering more classical in this regime.Comment: final version to appear in Phys. Rev.

Meson - nucleon vertex form factors at finite temperature

In this paper the dependence of meson-nucleon-nucleon vertex form factors is studied as a function of termperature. The results are obtained starting from a zero temperature Bonn potential. The temperature dependence of the vertex form factors and radii is studied in the thermofield dynamics, a real-time operator formalism of finite temperature field theory. It is anticipated that these results will have an impact on the study of relativistic heavy-ion collisions as the critical temperature for the phase transition from hadronic to quark-gluon system is approached.Comment: 19 pages, Revtex, 11 figures (Ps), 171k

Influence of modal loss on the quantum state generation via cross-Kerr nonlinearity

In this work we investigate an influence of decoherence effects on quantum states generated as a result of the cross-Kerr nonlinear interaction between two modes. For Markovian losses (both photon loss and dephasing), a region of parameters when losses still do not lead to destruction of non-classicality is identified. We emphasize the difference in impact of losses in the process of state generation as opposed to those occurring in propagation channel. We show moreover, that correlated losses in modern realizations of schemes of large cross-Kerr nonlinearity might lead to enhancement of non-classicality.Comment: To appear in PR