50,352 research outputs found
Phase space solutions in scalar-tensor cosmological models
An analysis of the solutions for the field equations of generalized
scalar-tensor theories of gravitation is performed through the study of the
geometry of the phase space and the stability of the solutions, with special
interest in the Brans-Dicke model. Particularly, we believe to be possible to
find suitable forms of the Brans-Dicke parameter omega and potential V of the
scalar field, using the dynamical systems approach, in such a way that they can
be fitted in the present observed scenario of the Universe.Comment: revtex, 2 pages, 4 eps figures, to appear in Brazilian Journal of
Physics (proceedings of the Conference 100 Years of Relativity, Sao Paulo,
Brazil, August 2005
Correlated electrons systems on the Apollonian network
Strongly correlated electrons on an Apollonian network are studied using the
Hubbard model. Ground-state and thermodynamic properties, including specific
heat, magnetic susceptibility, spin-spin correlation function, double occupancy
and one-electron transfer, are evaluated applying direct diagonalization and
quantum Monte Carlo. The results support several types of magnetic behavior. In
the strong-coupling limit, the quantum anisotropic spin 1/2 Heisenberg model is
used and the phase diagram is discussed using the renormalization group method.
For ferromagnetic coupling, we always observe the existence of long-range
order. For antiferromagnetic coupling, we find a paramagnetic phase for all
finite temperatures.Comment: 7 pages, 8 figure
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
Coupled scalar fields Oscillons and Breathers in some Lorentz Violating Scenarios
In this work we discuss the impact of the breaking of the Lorentz symmetry on
the usual oscillons, the so-called flat-top oscillons, and the breathers. Our
analysis is performed by using a Lorentz violation scenario rigorously derived
in the literature. We show that the Lorentz violation is responsible for the
origin of a kind of deformation of the configuration, where the field
configuration becomes oscillatory in a localized region near its maximum value.
Furthermore, we show that the Lorentz breaking symmetry produces a displacement
of the oscillon along the spatial direction, the same feature is present in the
case of breathers. We also show that the effect of a Lorentz violation in the
flat-top oscillon solution is responsible by the shrinking of the flat-top.
Furthermore, we find analytically the outgoing radiation, this result indicates
that the amplitude of the outgoing radiation is controlled by the Lorentz
breaking parameter, in such away that this oscillon becomes more unstable than
its symmetric counterpart, however, it still has a long living nature
On the study of oscillons in scalar field theories: A new approach
In this work we study configurations in one-dimensional scalar field theory,
which are time-dependent, localized in space and extremely long-lived called
oscillons. It is investigated how the action of changing the minimum value of
the field configuration representing the oscillon affects its behavior. We find
that one of the consequences of this procedure, is the appearance of a pair of
oscillon-like structures presenting different amplitudes and frequencies of
oscillation. We also compare our analytical results to numerical ones, showing
excellent agreement
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