Search results for "General relativity and quantum cosmology"
showing 10 items of 941 documents
Rigid motions relative to an observer:L-rigidity
1996
A new definition of rigidity,L-rigidity, in general relativity is proposed. This concept is a special class of pseudorigid motions and therefore it depends on the chosen curveL. It is shown that, for slow-rotation steady motions in Minkowski space, weak rigidity andL-rigidity are equivalent. The methods of the PPN approximation are considered. In this formalism, the equations that characterizeL-rigidity are expressed. As a consequence, the baryon mass density is constant in first order, the stress tensor is constant in the comoving system, the Newtonian potential is constant along the lineL, and the gravitational field is constant along the lineL in the comoving system.
Simplicial Wheeler-DeWitt equation in 2+1 spacetime dimensions.
1993
We introduce an equation which rue suggest to be a simplicial counterpart to the Wheeler-DeWitt equation in 2 + 1 spacetime dimensions. Our approach is based on the use of the Ashtekar variables
The Random-Phase Approximation
2007
In this chapter we extend the TDA particle-hole formalism of Chap. 9 to include correlations in the nuclear ground state. This sophisticated particle-hole formalism is called the random-phase approximation (RPA). In this description the simple Hartree-Fock particle-hole vacuum is replaced by a correlated ground state involving many-particle-many-hole excitations of the simple particle-hole vacuum. The resulting configuration mixing in excited states is more involved in the RPA than it is in the TDA. The ground-state correlations induce both particle-hole and hole-particle components in the RPA wave function.
Numerical relativistic hydrodynamics: Local characteristic approach.
1991
We extend some recent Ishock capturing methodsR designed to solve nonlinear hyperbolic systems of conservation laws and which avoid the use of artifical viscosity for treating strong discontinuities to a relativistic hydrodynamics system of equations. Some standard shock-tube problems and radial accretion onto a Schwarzschild black hole are used to calibrate our code.
New solutions of the hamiltonian and diffeomorphism constraints of quantum gravity from a highest weight loop representation
1991
Abstract We introduce a highest weight type representation of the Rovelli-Smolin algebra of loop observables for quantum gravity. In terms of this representation, new solutions of the hamiltonian and diffeomorphism constraints are given. Assuming the locality of the quantum hamiltonian constraint we show that any functional depending on the generalized link class of the disjoint union of arbitrary simple loops is a solution. Finally we argue that this is the general solution in the irreducible representation space.
A simple microsuperspace model in 2 + 1 spacetime dimensions
1992
Abstract We quantize the closed Friedmann model in 2 + 1 spacetime dimensions using euclidean path-integral approach and a simple microsuperspace model. A relationship between integration measure and operator ordering in the Wheeler-DeWitt equation is found within our model. Solutions to the Wheeler-DeWitt equation are exactly reproduced from the path integral using suitable integration contours in the complex plane.
An intrinsic characterization of the Schwarzschild metric
1998
An intrinsic algorithm that exclusively involves conditions on the metric tensor and its differential concomitants is presented to identify every type-D static vacuum solution. In particular, the necessary and sufficient explicit and intrinsic conditions are given for a Lorentzian metric to be the Schwarzschild solution.
The Quantum Scalar Field in Spherically Symmetric Loop Quantum Gravity
2013
We consider the quantization of a spherically symmetric gravitational system coupled to a massless scalar field within the loop quantum gravity framework. Our results rely on the uniform discretizations method developed during the last years. We minimize the associated discrete “master constraint” using a trial state whose gravitational part is peaked around the classical Schwarzschild solution.
Aligned Electric and Magnetic Weyl Fields
2003
We analyze the spacetimes admitting a direction for which the relative electric and magnetic Weyl fields are aligned. We give an invariant characterization of these metrics and study the properties of its Debever null vectors. The directions 'observing' aligned electric and magnetic Weyl fields are obtained for every Petrov type. The results on the no existence of purely magnetic solutions are extended to the wider class having homothetic electric and magnetic Weyl fields.
A covariant determination of the Weyl canonical frames in Petrov type I spacetimes
1997
A covariant algorithm is given to obtain principal 2-forms, Debever null directions and canonical frames associated with Petrov type I Weyl tensors. The relationship between these Weyl elements is explained, and their explicit expressions depending on Weyl invariants are obtained. These results are used to determine a cosmological observer in type I universes, and their usefulness in spacetime intrinsic characterization is shown.