arXiv subjects

Giovanni Modanese

Publications and source records attributed to Giovanni Modanese.

23 records · Page 2Linked to original sources

arXiv1998

"Tunneling" Amplitudes of a Massless Quantum Field

We propose a method for the approximate computation of the Green function of a scalar massless field subjected to potential barriers of given size and shape in spacetime. The potential of the barriers has the form V(phi)=xi(phi^2-phi_0^2)^2; xi is very large and phi_0 very close to zero, the product (xi phi_0^2) being finite and small. This is equivalent to the insertion of a suitable constraint in the functional integral for phi. The Green function contains a double Fourier transform of the characteristic function of the region where the potential has support.

math-ph↗

arXiv1994

Potential energy in quantum gravity

We give a general expression for the static potential energy of the gravitational interaction of two massive particles, in terms of an invariant vacuum expectation value of the quantized gravitational field. This formula holds for functional integral formulations of euclidean quantum gravity, regularized to avoid conformal instability. It could be regarded as the analogue of the Wilson loop of gauge theories and allows in principle, through numerical lattice simulations or other approximation techniques, non perturbative evaluations of the potential or of the effective coupling constant.

hep-th↗

arXiv1993

On the absence of localized curvature in the weak-coupling phase of quantum gravity

In the weak field expansion of euclidean quantum gravity, an analysis of the Wilson loops in terms of the gauge group, $SO(4)$, shows that the correspondent statistical system does not develope any configuration with localized curvature at low temperature. Such a ``non-local'' behavior contrasts strongly with that of usual gauge fields. We point out a possible relation between this result and those of the numerical simulations of quantum Regge Calculus. We also give a general quantum formula for the static potential energy of the gravitational interaction of two masses, which is compatible with the mentioned vacuum structure.

hep-th↗

arXiv1993

A formula for the static potential energy in quantum gravity

We give a general expression for the static potential energy of the gravitational interaction of two massive particles, in terms of an invariant vacuum expectation value of the quantized gravitational field. This formula holds for functional integral formulations of euclidean quantum gravity, regularized to avoid conformal instability. It could be regarded as the analogue of the Wilson loop for gauge theories and allows in principle, through numerical simulations or other approximation techniques, non perturbative evaluations of the potential or of the effective coupling constant. The geometrical meaning of this expression is quite simple, as it represents the ``average proper-time delay'', respect to two neighboring lines, of a very long geodesic with unit timelike tangent vector.

hep-th↗

arXiv1993

Wilson loops in four-dimensional quantum gravity

A Wilson loop is defined, in 4-D pure Einstein gravity, as the trace of the holonomy of the Christoffel connection or of the spin connection, and its invariance under the symmetry transformations of the action is showed (diffeomorphisms and local Lorentz transformations). We then compute the loop perturbatively, both on a flat background and in the presence of an external source; we also allow some modifications in the form of the action, and test the action of ``stabilized'' gravity. A geometrical analysis of the results in terms of the gauge group of the euclidean theory, $SO(4)$, leads us to the conclusion that the correspondent statistical system does not develope any configuration with localized curvature at low temperature. This ``non-local'' behavior of the quantized gravitational field strongly contrasts with that of usual gauge fields. Our results also provide an explanation for the absence of any invariant correlation of the curvature in the same approximation.

hep-th↗