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

TFD Approach to Bosonic Strings and DPD_{P}-branes

In this work we explain the construction of the thermal vacuum for the bosonic string, as well that of the thermal boundary state interpreted as a $D_{p}$-brane at finite temperature. In both case we calculate the respective entropy using the entropy operator of the Thermo Field Dynamics Theory. We show that the contribution of the thermal string entropy is explicitly present in the $D_{p}$-brane entropy. Furthermore, we show that the Thermo Field approach is suitable to introduce temperature in boundary states.Comment: 6 pages, revtex, typos are corrected. Prepared for the Second Londrina Winter School-Mathematical Methods in Physics, August 25-30, 2002, Londrina-Pr, Brazil. To appear in a special issue of IJMP

A New Kind of Uniformly Accelerated Reference Frames

A new kind of uniformly accelerated reference frames with a line-element different from the M{\o}ller and Rindler ones is presented, in which every observer at $x, y, z=$consts. has the same constant acceleration. The laws of mechanics are checked in the new kind of frames. Its thermal property is studied. The comparison with the M{\o}ller and Rindler uniform accelerated reference frames is also made.Comment: 10 pages, 2 figures. to appear in Int. J. Mod. Phys.

Maximum Entanglement in Squeezed Boson and Fermion States

A class of squeezed boson and fermion states is studied with particular emphasis on the nature of entanglement. We first investigate the case of bosons, considering two-mode squeezed states. Then we construct the fermion version to show that such states are maximum entangled, for both bosons and fermions. To achieve these results, we demonstrate some relations involving squeezed boson states. The generalization to the case of fermions is made by using Grassmann variables.Comment: 4 page

Spectra of Quarkonia at Finite Temperature

Finite-temperature spectra of heavy quarkonia are calculated by combining potential model and thermofield dynamics formalisms. The mass spectra of the heavy quarkonia with various quark contents are calculated. It is found that binding mass of the quarkonium decreases as temperature increases.Comment: 12 pages, 1 figure. To appear Mod.Phys.Lett.

Thermal DD-Brane Boundary States from Green-Schwarz Superstrings

In this paper we thermalize the type II superstrings in the GS formulation by applying the TFD formalism. The thermal boundary conditions on the thermal Hilbert space are obtained from the BPS $D$-brane boundary conditions at zero temperature. We show that thermal boundary states can be obtained by thermalization from the BPS $D$-branes at zero temperature. These new states can be interpreted as thermal $D$-branes. Next, we discuss the supersymmetry breaking of the thermal string in the TFD approach. We identify the broken supersymmetry with the $\epsilon$-transformation while the $\eta$-transformation is preserved. Also, we compute the thermal partition function and the entropy of the thermal string.Comment: 23 pages, LATeX fil

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

Lepton charge and neutrino mixing in pion decay processes

We consider neutrino mixing and oscillations in quantum field theory and compute the neutrino lepton charge in decay processes where neutrinos are generated. We also discuss the proper definition of flavor charge and states and clarify the issues of the possibility of different mass parameters in field mixing.Comment: 13 page

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

A Novel phase in the phase structure of the (gϕ4+hϕ6)1+1(g\phi^4 + h\phi^6)_{1+1} field theoretic model

In view of the newly discovered and physically acceptable $PT$ symmetric and non-Hermitian models, we reinvestigated the phase structure of the ($g\phi^{4}+h\phi^{6}$)$_{1+1}$ Hermitian model. The reinvestigation concerns the possibility of a phase transition from the original Hermitian and $PT$ symmetric phase to a non-Hermitian and $PT$ symmetric one. This kind of phase transition, if verified experimentally, will lead to the first proof that non-Hermitian and $PT$ symmetric models are not just a mathematical research framework but are a nature desire. To do the investigation, we calculated the effective potential up to second order in the couplings and found a Hermitian to Non-Hermitian phase transition. This leads us to introduce, for the first time, hermiticity as a symmetry which can be broken due to quantum corrections, \textit{i.e.}, when starting with a model which is Hermitian in the classical level, quantum corrections can break hermiticity while the theory stays physically acceptable. In fact, ignoring this phase will lead to violation of universality when comparing this model predictions with other models in the same class of universality. For instance, in a previous work we obtained a second order phase transition for the $PT$ symmetric and non-Hermitian $(-g\phi^{4})$ and according to universality, this phase should exist in the phase structure of the ($g\phi^{4}+h\phi^{6}$) model for negative $g$. Finally, among the novelties in this letter, in our calculation for the effective potential, we introduced a new renormalization group equation which describes the invariance of the bare vacuum energy under the change of the scale. We showed that without this invariance, the original theory and the effective one are inequivalent.Comment: 13 pages, 4 figure