751 research outputs found
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
Spectral properties of a spin-incoherent Luttinger Liquid
We present time-dependent density matrix renormalization group (DMRG) results
for strongly interacting one dimensional fermionic systems at finite
temperature. When interactions are strong the characteristic spin energy can be
greatly suppressed relative to the characteristic charge energy, allowing for
the possibility of spin-incoherent Luttinger liquid physics when the
temperature is high compared to the spin energy, but small compared to the
charge energy. Using DMRG we compute the spectral properties of the model
at arbitrary temperatures with respect to both spin and charge energies. We
study the full crossover from the Luttinger liquid regime to the
spin-incoherent regime,focusing on small , where the signatures of
spin-incoherent behavior are more manifest. Our method allows us to access the
analytically intractable regime where temperature is of the order of the spin
energy, . Our results should be helpful in the interpretation of
experiments that may be in the crossover regime, , and apply to
one-dimensional cold atomic gases where finite-temperature effects are
appreciable. The technique may also be used to guide the development of
analytical approximations for the crossover regime.Comment: 7 pages, 5 figure
Confined Phase In The Real Time Formalism And The Fate Of The World Behind The Horizon
In the real time formulation of finite temperature field theories, one
introduces an additional set of fields (type-2 fields) associated to each field
in the original theory (type-1 field). In hep-th/0106112, in the context of the
AdS-CFT correspondence, Maldacena interpreted type-2 fields as living on a
boundary behind the black hole horizon. However, below the Hawking-Page
transition temperature, the thermodynamically preferred configuration is the
thermal AdS without a black hole, and hence there are no horizon and boundary
behind it. This means that when the dual gauge theory is in confined phase, the
type-2 fields cannot be associated with the degrees of freedom behind the black
hole horizon. I argue that in this case the role of the type-2 fields is to
make up bulk type-2 fields of classical closed string field theory on AdS at
finite temperature in the real time formalism.Comment: v2: cases divided into sections with more detailed explanations.
considerably enlarged with examples and a lot of figures. sec 4.1.2 for
general closed cut-out circuits and appendix A for a sample calculation newly
added. many minor corrections and clarifying comments. refs added. v3: refs
and related discussion added. 1+46 pages, 26 figures. published versio
Vacuum structure for expanding geometry
We consider gravitational wave modes in the FRW metrics in a de Sitter phase
and show that the state space splits into many unitarily inequivalent
representations of the canonical commutation relations. Non-unitary time
evolution is described as a trajectory in the space of the representations. The
generator of time evolution is related to the entropy operator. The
thermodynamic arrow of time is shown to point in the same direction of the
cosmological arrow of time. The vacuum is a two-mode SU(1,1) squeezed state of
thermo field dynamics. The link between expanding geometry, squeezing and
thermal properties is exhibited.Comment: Latex file, epsfig, 1 figure, 21 page
Condensation in Globally Coupled Populations of Chaotic Dynamical Systems
The condensation transition, leading to complete mutual synchronization in
large populations of globally coupled chaotic Roessler oscillators, is
investigated. Statistical properties of this transition and the cluster
structure of partially condensed states are analyzed.Comment: 11 pages, 4 figures, revte
Thermal Bogoliubov transformation in nuclear structure theory
Thermal Bogoliubov transformation is an essential ingredient of the thermo
field dynamics -- the real time formalism in quantum field and many-body
theories at finite temperatures developed by H. Umezawa and coworkers. The
approach to study properties of hot nuclei which is based on the extension of
the well-known Quasiparticle-Phonon Model to finite temperatures employing the
TFD formalism is presented. A distinctive feature of the QPM-TFD combination is
a possibility to go beyond the standard approximations like the thermal
Hartree-Fock or the thermal RPA ones.Comment: 8 pages, Proceedings of the International Bogolyubov Conference
"Problems of Theoretical and Mathematical Physics", August 23 -- 27, 2009,
Dubna, Russi
Cortical phase transitions, non-equilibrium thermodynamics and the time-dependent Ginzburg-Landau equation
The formation of amplitude modulated and phase modulated assemblies of
neurons is observed in the brain functional activity. The study of the
formation of such structures requires that the analysis has to be organized in
hierarchical levels, microscopic, mesoscopic, macroscopic, each with its
characteristic space-time scales and the various forms of energy, electric,
chemical, thermal produced and used by the brain. In this paper, we discuss the
microscopic dynamics underlying the mesoscopic and the macroscopic levels and
focus our attention on the thermodynamics of the non-equilibrium phase
transitions. We obtain the time-dependent Ginzburg-Landau equation for the
non-stationary regime and consider the formation of topologically non-trivial
structures such as the vortex solution. The power laws observed in functional
activities of the brain is also discussed and related to coherent states
characterizing the many-body dissipative model of brain.Comment: 19 pages, 4 figures, research pape
Quantum-classical crossover in electrodynamics
A classical field theory is proposed for the electric current and the
electromagnetic field interpolating between microscopic and macroscopic
domains. It represents a generalization of the density functional for the
dynamics of the current and the electromagnetic field in the quantum side of
the crossover and reproduces standard classical electrodynamics on the other
side. The effective action derived in the closed time path formalism and the
equations of motion follow from the variational principle. The polarization of
the Dirac-see can be taken into account in the quadratic approximation of the
action by the introduction of the deplacement field strengths as in
conventional classical electrodynamics. Decoherence appears naturally as a
simple one-loop effect in this formalism. It is argued that the radiation time
arrow is generated from the quantum boundary conditions in time by decoherence
at the quantum-classical crossover and the Abraham-Lorentz force arises from
the accelerating charge or from other charges in the macroscopic or the
microscopic side, respectively. The functional form of quantum renormalization
group, the generalization of the renormalization group method for the density
matrix, is proposed to follow the scale dependence through the
quantum-classical crossover in a systematical manner.Comment: new references added, few sign errors fixed, to appear in Physical
Review
Massless Thirring model in canonical quantization scheme
It is shown that the exact solvability of the massless Thirring model in the
canonical quantization scheme originates from the intrinsic linearizability of
its Heisenberg equations in the method of dynamical mappings. The corresponding
role of inequivalent representations of free massless Dirac field is
elucidated.Comment: 10 page
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