Generalizations of the thermal Bogoliubov transformation

The thermal Bogoliubov transformation in thermo field dynamics is generalized in two respects. First, a generalization of the $\alpha$--degree of freedom to tilde non--conserving representations is considered. Secondly, the usual $2\times2$ Bogoliubov matrix is extended to a $4\times4$ matrix including mixing of modes with non--trivial multiparticle correlations. The analysis is carried out for both bosons and fermions.Comment: 20 pages, Latex, Nordita 93/33

String Entanglement and D-branes as Pure States

We study the entanglement of closed strings degrees of freedom in order to investigate the microscopic structure and statistics of objects as D-branes. By considering the macroscopic pure state (MPS) limit, whenever the entanglement entropy goes to zero (in such a way that the macroscopic properties of the state are preserved), we show that boundary states may be recovered in this limit and, furthermore, the description through closed string (perturbative) degrees of freedom collapses. We also show how the thermal properties of branes and closed strings could be described by this model, and it requires that dissipative effects be taken into account. Extensions of the MPS analysis to more general systems at finite temperature are finally emphasized.Comment: 14 pages. Minor improvements. Published in Phys. Rev.

Wigner functions of thermo number state, photon subtracted and added thermo vacuum state at finite temperature

Based on Takahashi-Umezawa thermo field dynamics and the order-invariance of Weyl ordered operators under similar transformations, we present a new approach to deriving the exact Wigner functions of thermo number state, photon subtracted and added thermo vacuum state. We find that these Wigner functions are related to the Gaussian-Laguerre type functions of temperature, whose statistical properties are then analysed.Comment: 10 pages and 2 figure

No-cloning theorem in thermofield dynamics

We discuss the relation between the no-cloning theorem from quantum information and the doubling procedure used in the formalism of thermofield dynamics (TFD). We also discuss how to apply the no-cloning theorem in the context of thermofield states defined in TFD. Consequences associated to mixed states, von Neumann entropy and thermofield vacuum are also addressed.Comment: 16 pages, 3 figure

Strong CP violation and chiral symmetry breaking in hot and dense quark matter

We investigate chiral symmetry breaking and strong CP violation effects in the phase diagram of strongly interacting matter. We demonstrate the effect of strong CP violating terms on the phase structure at finite temperature and densities in a 3-flavor Nambu-Jona-Lasinio (NJL) model including the Kobayashi-Maskawa-t'Hooft (KMT) determinant term. This is investigated using an explicit structure for the ground state in terms of quark-antiquark condensates for both in the scalar and the pseudoscalar channels. CP restoring transition with temperature at zero baryon density is found to be a second order transition at $\theta = \pi$ while the same at finite chemical potential and small temperature turns out to be a first order transition. Within the model, the tri-critical point turns out to be $(T_c,\mu_c)\simeq(273,94)$ MeV at $\theta = \pi$ for such a transition.Comment: 10 pages, 12 figure

Diagonalization of full finite temperature Green's function by quasi-particles

For thermal systems, standard perturbation theory breaks down because of the absence of stable, observable asymptotic states. We show, how the introduction of {\it statistical} quasi-particles (stable, but not observable) gives rise to a consistent description. Statistical and spectral information can be cleanly separated also for interacting systems.Comment: 9 pages in standard LaTe

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

The unmasking of thermal Goldstone bosons

The problem of extracting the modes of Goldstone bosons from a thermal background is reconsidered in the framework of relativistic quantum field theory. It is shown that in the case of spontaneous breakdown of an internal bosonic symmetry a recently established decomposition of thermal correlation functions contains certain specific contributions which can be attributed to a particle of zero mass.Comment: 7 pages, LaTeX; new and considerably strengthened results after Eq. (14); to appear in Phys. Rev.

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