1,284 research outputs found
Wyman's solution, self-similarity and critical behaviour
We show that the Wyman's solution may be obtained from the four-dimensional
Einstein's equations for a spherically symmetric, minimally coupled, massless
scalar field by using the continuous self-similarity of those equations. The
Wyman's solution depends on two parameters, the mass and the scalar charge
. If one fixes to a positive value, say , and let
take values along the real line we show that this solution exhibits critical
behaviour. For the space-times have eternal naked singularities,
for one has a Schwarzschild black hole of mass and finally
for one has eternal bouncing solutions.Comment: Revtex version, 15pages, 6 figure
The anomaly-induced effective action and natural inflation
The anomaly-induced inflation (modified Starobinsky model) is based on the
application of the effective quantum field theory approach to the Early
Universe. We present a brief general review of the model and show that it does
not require a fine-tuning for the parameters of the theory or initial data,
gives a real chance to meet a graceful exit to the FRW phase and also has
positive features with respect to the metric perturbations.Comment: Invited talk at the International Workshop on Astroparticle and High
Energy Physics, October 14 - 18, 2003, Valencia, Spai
Anomalous Hall effect in NiPt thin films
We study Hall effect in sputtered NixPt1-x thin films with different Ni
concentrations. Temperature, magnetic field and angular dependencies are
analyzed and the phase diagram of NiPt thin films is obtained. It is found that
films with sub-critical Ni concentration exhibit cluster-glass behavior at low
temperatures with a perpendicular magnetic anisotropy below the freezing
temperature. Films with over-critical Ni concentration are ferromagnetic with
parallel anisotropy. At the critical concentration the state of the film is
strongly frustrated. Such films demonstrate canted magnetization with the easy
axis rotating as a function of temperature. The magnetism appears via
consecutive paramagnetic - cluster glass - ferromagnetic transitions, rather
than a single second-order phase transition. But most remarkably, the
extraordinary Hall effect changes sign at the critical concentration. We
suggest that this is associated with a reconstruction of the electronic
structure of the alloy at the normal metal - ferromagnet quantum phase
transition.Comment: 12 pages, 17 figure
Supersymmetrization of the Radiation Damping
We construct a supersymmetrized version of the model to the radiation damping
\cite{03} introduced by the present authors \cite{ACWF}. We dicuss its
symmetries and the corresponding conserved Noether charges. It is shown this
supersymmetric version provides a supersymmetric generalization of the Galilei
algebra obtained in \cite{ACWF}. We have shown that the supersymmetric action
can be splited into dynamically independent external and internal sectors.Comment: 9 page
Noncommutative Metafluid Dynamics
In this paper we define a noncommutative (NC) Metafluid Dynamics
\cite{Marmanis}. We applied the Dirac's quantization to the Metafluid Dynamics
on NC spaces. First class constraints were found which are the same obtained in
\cite{BJP}. The gauge covariant quantization of the non-linear equations of
fields on noncommutative spaces were studied. We have found the extended
Hamiltonian which leads to equations of motion in the gauge covariant form. In
addition, we show that a particular transformation \cite{Djemai} on the usual
classical phase space (CPS) leads to the same results as of the
-deformation with . Besides, we will shown that an additional
term is introduced into the dissipative force due the NC geometry. This is an
interesting feature due to the NC nature induced into model.Comment: 11 page
Birth and evolution of a dense coronal loop in a complex flare region
<p><b>Context:</b> During the 14th/15th of April 2002, several flares occurred in NOAA active region complex 9893/9910. Two of these were previously interpreted as having anomalously high coronal column densities.</p>
<p><b>Aims:</b> We develop a scenario using multiwavelength observations to explain the high coronal column density (1020 cm-2) present at the onset of the 14th April 2002 M3.7 hard X-ray event.</p>
<p><b>Methods:</b> Prior to this event a series of flares occurred in close temporal and spatial proximity. We observe the sequence of flares in a multiwavelength regime from radio to hard X-rays. This allows us to study the particle acceleration and plasma evaporation in these events.</p>
<p><b>Results:</b> The observations of these flares lead us to propose a sequence of reconnections between multiple systems of loops in a 3 dimensional field geometry. We suggest that the dense loops in the M3.7 event can be explained as being already filled with plasma from the earlier events; these loops then themselves become unstable or reconnect leading to particle acceleration into an overdense coronal environment. We explore the possibility that a high-beta disruption is behind the instability of these dense loops, leading to the 14th April 2002 M3.7 event and the observation of hard X-rays in the corona at energies up to ≈ 50 keV.</p>
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