14,724 research outputs found
Trumpet Slices in Kerr Spacetimes
We introduce a new time-independent family of analytical coordinate systems
for the Kerr spacetime representing rotating black holes. We also propose a
(2+1)+1 formalism for the characterization of trumpet geometries. Applying this
formalism to our new family of coordinate systems we identify, for the first
time, analytical and stationary trumpet slices for general rotating black
holes, even for charged black holes in the presence of a cosmological constant.
We present results for metric functions in this slicing and analyze the
geometry of the rotating trumpet surface.Comment: 5 pages, 2 figures; version published in PR
Fully covariant and conformal formulation of the Z4 system in a reference-metric approach: comparison with the BSSN formulation in spherical symmetry
We adopt a reference-metric approach to generalize a covariant and conformal
version of the Z4 system of the Einstein equations. We refer to the resulting
system as ``fully covariant and conformal", or fCCZ4 for short, since it is
well suited for curvilinear as well as Cartesian coordinates. We implement this
fCCZ4 formalism in spherical polar coordinates under the assumption of
spherical symmetry using a partially-implicit Runge-Kutta (PIRK) method and
show that our code can evolve both vacuum and non-vacuum spacetimes without
encountering instabilities. Our method does not require regularization of the
equations to handle coordinate singularities, nor does it depend on
constraint-preserving outer boundary conditions, nor does it need any
modifications of the equations for evolutions of black holes. We perform
several tests and compare the performance of the fCCZ4 system, for different
choices of certain free parameters, with that of BSSN. Confirming earlier
results we find that, for an optimal choice of these parameters, and for
neutron-star spacetimes, the violations of the Hamiltonian constraint can be
between 1 and 3 orders of magnitude smaller in the fCCZ4 system than in the
BSSN formulation. For black-hole spacetimes, on the other hand, any advantages
of fCCZ4 over BSSN are less evident.Comment: 13 pages, 10 figure
How the Polyakov loop and the regularization affect strangeness and restoration of symmetries at finite T
The effects of the Polyakov loop and of a regularization procedure that
allows the presence of high momentum quark states at finite temperature is
investigated within the Polyakov-loop extended Nambu--Jona-Lasinio model. The
characteristic temperatures, as well as the behavior of observables that signal
deconfinement and restoration of chiral and axial symmetries, are analyzed,
paying special attention to the behavior of strangeness degrees of freedom. We
observe that the cumulative effects of the Polyakov loop and of the
regularization procedure contribute to a better description of the
thermodynamics, as compared with lattice estimations. We find a faster partial
restoration of chiral symmetry and the restoration of the axial symmetry
appears as a natural consequence of the full recovering of the chiral symmetry
that was dynamically broken. These results show the relevance of the effects of
the interplay among the Polyakov loop dynamics, the high momentum quark sates
and the restoration of the chiral and axial symmetries at finite temperature.Comment: Talk given at XIII International Conference on Hadron Spectroscopy
(Hadron 2009), Tallahassee, Florida, USA, 29 Nov - 4 Dec, 200
Reheating via a generalized non-minimal coupling of curvature to matter
In this work one shows that a generalized non-minimal coupling between
geometry and matter is compatible with Starobinsky inflation and leads to a
successful process of preheating, a reheating scenario based on the production
of massive particles via parametric resonance. The model naturally extends the
usual preheating mechanism, which resorts to an {\it ad-hoc} scalar
curvature-dependent mass term for a scalar field , and also encompasses a
previously studied preheating channel based upon a non-standard kinetic term.Comment: 12 page
The Creation of Defects with Core Condensation
Defects in superfluid 3He, high-Tc superconductors, QCD colour superfluids
and cosmic vortons can possess (anti)ferromagnetic cores, and their
generalisations. In each case there is a second order parameter whose value is
zero in the bulk which does not vanish in the core. We examine the production
of defects in the simplest 1+1 dimensional scalar theory in which a second
order parameter can take non-zero values in a defect core. We study in detail
the effects of core condensation on the defect production mechanism.Comment: 9 pages, 7 figures, small corrections, 2 references added, final
version to be published in PR
Dynamical properties across a quantum phase transition in the Lipkin-Meshkov-Glick model
It is of high interest, in the context of Adiabatic Quantum Computation, to
better understand the complex dynamics of a quantum system subject to a
time-dependent Hamiltonian, when driven across a quantum phase transition. We
present here such a study in the Lipkin-Meshkov-Glick (LMG) model with one
variable parameter. We first display numerical results on the dynamical
evolution across the LMG quantum phase transition, which clearly shows a
pronounced effect of the spectral avoided level crossings. We then derive a
phenomenological (classical) transition model, which already shows some
closeness to the numerical results. Finally, we show how a simplified quantum
transition model can be built which strongly improve the classical approach,
and shed light on the physical processes involved in the whole LMG quantum
evolution. From our results, we argue that the commonly used description in
term of Landau-Zener transitions is not appropriate for our model.Comment: 7 pages, 5 figures; corrected reference
Anti-de Sitter wormhole kink
The metric describing a given finite sector of a four-dimensional
asymptotically anti-de Sitter wormhole can be transformed into the metric of
the time constant sections of a Tangherlini black hole in a five-dimensional
anti-de Sitter spacetime when one allows light cones to tip over on the
hypersurfaces according to the conservation laws of an one-kink. The resulting
kinked metric can be maximally extended, giving then rise to an instantonic
structure on the euclidean continuation of both the Tangherlini time and the
radial coordinate. In the semiclassical regime, this kink is related to the
existence of closed timelike curves.Comment: 10 pages, to appear in IJMP
General Pattern Search Applied to the Optimization of the Shell and Tube Heat Exchanger
The literature has different implementations and results for the mono-objective and multiobjective optimization of the shell and tube heat exchanger (STHE), most of them using evolutionary computation. However, there is a gap to find the optimal solution of this problem through direct search methods (numerical optimization). So, this paper uses the Pattern Search algorithm of MATLAB toolbox applied to this case study
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