6,765 research outputs found
Onset of classical behaviour after a phase transition
We analyze the onset of classical behaviour in a scalar field after a
continuous phase transition, in which the system-field, the long wavelength
order parameter of the model, interacts with an environment of its own
short-wavelength modes. We compute the decoherence time for the system-field
modes from the master equation and compare it with the other time scales of the
model. Within our approximations the decoherence time is in general the
smallest dynamical time scale. Demanding diagonalisation of the decoherence
functional produces identical results. The inclusion of other environmental
fields makes diagonalisation occur even earlier.Comment: Seven pages, no figures. Contributed talk to the Second International
Workshop DICE2004, Piombino, Italy. To be published in the Brazilian Journal
of Physic
Decoherence in a Two Slit Diffraction Experiment with Massive Particles
Matter-wave interferometry has been largely studied in the last few years.
Usually, the main problem in the analysis of the diffraction experiments is to
establish the causes for the loss of coherence observed in the interference
pattern. In this work, we use different type of environmental couplings to
model a two slit diffraction experiment with massive particles. For each model,
we study the effects of decoherence on the interference pattern and define a
visibility function that measures the loss of contrast of the interference
fringes on a distant screen. Finally, we apply our results to the experimental
reported data on massive particles .Comment: 6 pages, 3 figure
Geometrical properties of Riemannian superspaces, observables and physical states
Classical and quantum aspects of physical systems that can be described by
Riemannian non degenerate superspaces are analyzed from the topological and
geometrical points of view. For the N=1 case the simplest supermetric
introduced in [Physics Letters B \textbf{661}, (2008),186] have the correct
number of degrees of freedom for the fermion fields and the super-momentum
fulfil the mass shell condition, in sharp contrast with other cases in the
literature where the supermetric is degenerate. This fact leads a deviation of
the 4-impulse (e.g. mass constraint) that can be mechanically interpreted as a
modification of the Newton's law. Quantum aspects of the physical states and
the basic states and the projection relation between them, are completely
described due the introduction of a new Majorana-Weyl representation of the
generators of the underlying group manifold. A new oscillatory fermionic effect
in the part of the vaccum solution involving the chiral and antichiral
components of this Majorana bispinor is explicitly shown.Comment: 16 pags. 3 figures. To Anna Grigorievna Kartavenko and Academic
Professor Alexei Norianovich Sissakian, in memoria
How Phase Transitions induce classical behaviour
We continue the analysis of the onset of classical behaviour in a scalar
field after a continuous phase transition, in which the system-field, the long
wavelength order parameter of the model, interacts with an environment, of its
own short-wavelength modes and other fields, neutral and charged, with which it
is expected to interact. We compute the decoherence time for the system-field
modes from the master equation and directly from the decoherence functional
(with identical results). In simple circumstances the order parameter field is
classical by the time the transition is complete.Comment: 10 pages, 1 figure: To be published in the International Journal of
Theoretical Physics (2005) as part of the Proceedings of the "Peyresq Physics
9" meeting (2004) on "Micro and Macro structures of spacetime",ed. E.
Verdague
4D quantum black hole physics from 2D models?
Minimally coupled 4D scalar fields in Schwarzschild space-time are
considered. Dimensional reduction to 2D leads to a well known anomaly induced
effective action, which we consider here in a local form with the introduction
of auxiliary fields. Boundary conditions are imposed on them in order to select
the appropriate quantum states (Boulware, Unruh annd Israel-Hartle-Hawking).
The stress tensor is then calculated and its comparison with the expected 4D
form turns out to be unsuccessful. We also critically discuss in some detail a
recent controversial result appeared in the literature on the same topic.Comment: latex, 13 pages; misprints corrected, references adde
Rotating charged Black Holes in Einstein-Born-Infeld theories and their ADM mass
In this work, the solution of the Einstein equations for a slowly rotating
black hole with Born-Infeld charge is obtained. Geometrical properties and
horizons of this solution are analyzed. The conditions when the ADM mass (as in
the nonlinear static cases) and the ADM angular momentum of the system have
been modified by the non linear electromagnetic field of the black hole, are
considered.Comment: Final version and figures in journal. References and comments adde
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