43,786 research outputs found
Parametric Competition in non-autonomous Hamiltonian Systems
In this work we use the formalism of chord functions (\emph{i.e.}
characteristic functions) to analytically solve quadratic non-autonomous
Hamiltonians coupled to a reservoir composed by an infinity set of oscillators,
with Gaussian initial state. We analytically obtain a solution for the
characteristic function under dissipation, and therefore for the determinant of
the covariance matrix and the von Neumann entropy, where the latter is the
physical quantity of interest. We study in details two examples that are known
to show dynamical squeezing and instability effects: the inverted harmonic
oscillator and an oscillator with time dependent frequency. We show that it
will appear in both cases a clear competition between instability and
dissipation. If the dissipation is small when compared to the instability, the
squeezing generation is dominant and one can see an increasing in the von
Neumann entropy. When the dissipation is large enough, the dynamical squeezing
generation in one of the quadratures is retained, thence the growth in the von
Neumann entropy is contained
A note on the infrared behavior of the compactified Ginzburg--Landau model in a magnetic field
We consider the Euclidean large- Ginzburg--Landau model in dimensions,
() of them being compactified. For D=3, the system can be supposed
to describe, in the cases of d=1, d=2, and d=3, respectively, a superconducting
material in the form of a film, of an infinitely long wire having a rectangular
cross-section and of a brick-shaped grain. We investigate the fixed-point
structure of the model, in the presence of an external magnetic field. An
infrared-stable fixed points is found, which is independent of the number of
compactified dimensions. This generalizes previous work for type-II
superconducting filmsComment: LATEX, 6 pages no figures. arXiv admin note: 80% of text overlaps
with arXiv:1102.139
- …