arXiv subjects

Vittorio de Alfaro

Publications and source records attributed to Vittorio de Alfaro.

10 recordsLinked to original sources

arXiv1999

Static Quantization of Two-dimensional Dilaton Gravity and Black Holes

Two-dimensional matterless dilaton gravity is a topological theory and can be classically reduced to a (0+1)-dimensional theory with a finite number of degrees of freedom. If quantization is performed, a simple gauge invariant quantum mechanics is obtained. The properties of the gauge invariant operators and of the Hilbert space of physical states can be determined. In particular, for N-dimensional pure gravity with (N-2)-dimensional spherical symmetry, the square of the ADM mass operator is self-adjoint, not the mass itself.

hep-th↗

arXiv1998

Quantization of the String Inspired Dilaton Gravity and the Birkhoff Theorem

We develop a simple scheme of quantization for the dilaton CGHS model without scalar fields, that uses the Gupta-Bleuler approach for the string fields. This is possible because the constraints can be linearized classically, due to positivity conditions that are present in the model (and not in the general string case). There is no ambiguity nor anomalies in the quantization. The expectation values of the metric and dilaton fields obey the classical requirements, thus exhibiting at the quantum level the Birkhoff theorem.

hep-th↗

arXiv1997

The Birkhoff Theorem in the Quantum Theory of Two-Dimensional Dilaton Gravity

In classical two-dimensional pure dilaton gravity, and in particular in spherically symmetric pure gravity in d dimensions, the generalized Birkhoff theorem states that, for a suitable choice of coordinates, the metric coefficients are only functions of a single coordinate. It is interesting to see how this result is recovered in quantum theory by the explicit construction of the Hilbert space. We examine the CGHS model, enforce the set of auxiliary conditions that select physical states a` la Gupta-Bleuler, and prove that the matrix elements of the metric and of the dilaton field obey the classical requirement. We introduce the mass operator and show that its eigenvalue is the only gauge invariant label of states. Thus the Hilbert space is equivalent to that obtained by quantum mechanical treatment of the static case. This is the quantum form of the Birkhoff theorem for this model.

hep-th↗

arXiv1996

Time Gauge Fixing and Hilbert Space in Quantum String Cosmology

Recently the low-energy effective string theory has been used by Gasperini and Veneziano to elaborate a very interesting scenario for the early history of the universe (``birth of the universe as quantum scattering''). Here we investigate the gauge fixing and the problem of the definition of a global time parameter for this model, and we obtain the positive norm Hilbert space of states.

gr-qc↗

arXiv1996

Quantization of a 2D Minisuperspace Model in Dilaton-Einstein Gravity

We investigate a minisuperspace model of Einstein gravity plus dilaton that describes a static spherically symmetric configuration or a Kantowski - Sachs like universe. We develop the canonical formalism and identify canonical quantities that generate rigid symmetries of the Hamiltonian. Quantization is performed by the Dirac and the reduced methods. Both approaches lead to the same positive definite Hilbert space.

gr-qc↗

arXiv1995

Quantization of the Schwarzschild Black Hole

We quantize by the Dirac - Wheeler-DeWitt method the canonical formulation of the Schwarzschild black hole developed in a previous paper. We investigate the properties of the operators that generate rigid symmetries of the Hamiltonian, establish the form of the invariant measure under the rigid transformations, and determine the gauge fixed Hilbert space of states. We also prove that the reduced quantization method leads to the same Hilbert space for a suitable gauge fixing.

gr-qc↗

arXiv1994

Hamiltonian Formalism for Black Holes and Quantization

Starting from the Lagrangian formulation of the Einstein equations for the vacuum static spherically symmetric metric, we develop a canonical formalism in the radial variable $r$ that is time--like inside the Schwarzschild horizon. The Schwarzschild mass turns out to be represented by a canonical function that commutes with the $r$--Hamiltonian. We investigate the Wheeler--DeWitt quantization and give the general representation for the solution as superposition of eigenfunctions of the mass operator.

gr-qc↗

arXiv1994

A Schrodinger Equation for Quantum Universes

We discuss how to fix the gauge in the canonical treatment of Lagrangians, with finite number of degrees of freedom, endowed with time reparametrization invariance. The motion can then be described by an effective Hamiltonian acting on the gauge shell canonical space. The system is then suited for quantization. We apply this treatment to the case of a Robertson--Walker metric interacting with zero modes of bosonic fields and write a §equation for the on--shell wave function (Presented at the International Workshop ``Birth of the Universe and Fundamental Physics'', Rome, May 18-21, 1994).

gr-qc↗

arXiv1994

A SCHRÖdinger Equation for Mini Universes

gr-qc↗

arXiv1993

On a Quantum Universe Filled with Yang - Mills Radiation

We investigate the properties of a quantum Robertson - Walker universe described by the Wheeler -- DeWitt equation. The universe is filled with a quantum Yang -- Mills uniform field. This is then a quantum mini copy of the standard model of our universe. We discuss the interpretation of the Wheeler -- DeWitt wave function using the correspondence principle to connect $\vertψ\vert^2$ for large quantum numbers to the classical probability for a radiation dominated universe. This can be done in any temporal gauge. The correspondence principle determines the Schrödinger representation of the momentum associated to the gravitational degree of freedom. We also discuss the measure in the mini--superspace needed to ensure invariance of the quantum description under change of the temporal gauge. Finally, we examine the behaviour of $\vertψ\vert^2$ in inflationary conditions.

gr-qc↗