205,139 research outputs found
Cosmological perturbations in FRW model with scalar field within Hamilton-Jacobi formalism and symplectic projector method
The Hamilton-Jacobi analysis is applied to the dynamics of the scalar
fluctuations about the Friedmann-Robertson-Walker (FRW). The gauge conditions
are found from the consistency conditions. The physical degrees of freedom of
the model are obtain by symplectic projector method. The role of the linearly
dependent Hamiltonians and the gauge variables in Hamilton-Jacobi formalism is
discussed.Comment: 11 page
Operatorial quantization of Born-Infeld Skyrmion model and hidden symmetries
The SU(2) collective coordinates expansion of the Born-Infeld\break Skyrmion
Lagrangian is performed. The classical Hamiltonian is computed from this
special Lagrangian in approximative way: it is derived from the expansion of
this non-polynomial Lagrangian up to second-order variable in the collective
coordinates. This second-class constrained model is quantized by Dirac
Hamiltonian method and symplectic formalism. Although it is not expected to
find symmetries on second-class systems, a hidden symmetry is disclosed by
formulating the Born-Infeld Skyrmion %model as a gauge theory. To this end we
developed a new constraint conversion technique based on the symplectic
formalism. Finally, a discussion on the role played by the hidden symmetry on
the computation of the energy spectrum is presented.Comment: A new version of hep-th/9901133. To appear in JP
Observer Dependent Horizon Temperatures: a Coordinate-Free Formulation of Hawking Radiation as Tunneling
We reformulate the Hamilton-Jacobi tunneling method for calculating Hawking
radiation in static, spherically-symmetric spacetimes by explicitly
incorporating a preferred family of frames. These frames correspond to a family
of observers tied to a locally static timelike Killing vector of the spacetime.
This formulation separates the role of the coordinates from the choice of
vacuum and thus provides a coordinate-independent formulation of the tunneling
method. In addition, it clarifies the nature of certain constants and their
relation to these preferred observers in the calculation of horizon
temperatures. We first use this formalism to obtain the expected temperature
for a static observer at finite radius in the Schwarzschild spacetime. We then
apply this formalism to the Schwarzschild-de Sitter spacetime, where there is
no static observer with 4-velocity equal to the static timelike Killing vector.
It is shown that a preferred static observer, one whose trajectory is geodesic,
measures the lowest temperature from each horizon. Furthermore, this observer
measures horizon temperatures corresponding to the well-known Bousso-Hawking
normalization.Comment: 11 pages, 1 2-part figure, references added, appendix added,
discussion streamline
The Role of Ground State Correlations in the Single-Particle Strength of Odd Nuclei with Pairing
A method based on the consistent use of the Green function formalism has been
developed to calculate the distribution of the single-particle strength in odd
nuclei with pairing. The method takes into account the quasiparticle-phonon
interaction, ground state correlations and a "refinement" of phenomenological
single-particle energies and pairing gap values from the quasiparticle-phonon
interaction under consideration. The calculations for 121Sn and 119Sn that were
performed in the quasiparticlephonon approximation, have shown a
reasonable agreement with experiment. The ground state correlations play a
noticeable role and mostly improve the agreement with experiment or shift the
results to the right direction.Comment: 11 page
Calculation of the static and dynamical correlation energy of pseudo-one-dimensional beryllium systems via a many-body expansion
Low-dimensional beryllium systems constitute interesting case studies for the
test of correlation methods because of the importance of both static and
dynamical correlation in the formation of the bond. Aiming to describe the
whole dissociation curve of extended Be systems we chose to apply the method of
increments (MoI) in its multireference (MR) formalism. However, in order to do
so an insight into the wave function was necessary. Therefore we started by
focusing on the description of small Be chains via standard quantum chemical
methods and gave a brief analysis of the main characteristics of their wave
functions. We then applied the MoI to larger beryllium systems, starting from
the Be6 ring. First, the complete active space formalism (CAS-MoI) was employed
and the results were used as reference for local MR calculations of the whole
dissociation curve. Despite this approach is well established for the
calculation of systems with limited multireference character, its application
to the description of whole dissociation curves still requires further testing.
After discussing the role of the basis set, the method was finally applied to
larger rings and extrapolated to an infinite chain
Influence of the intermediate material on the singular stress field in tri-material junctions
According to the mathematical formalism of the eigenfunction expansion method, the problem of stress-singularities arising from multi-material junctions is addressed. The wedges are composed of isotropic homogeneous materials and are in a condition of plane stress or strain. The order of the stress-singularity is provided for tri-material junctions, paying special attention to the role played by Mode-I and Mode-II deformation. The effect of cracks inside either the softer or the stiffer material is also investigated. Numerical results can be profitably used for establishing optimum material configurations
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