OHP pp129 : Scintillation in scalar-tensor theories of gravity Next:Introduction

Scintillation in scalar-tensor theories of gravity

C.Bracco ^{1} and P.Teyssandier ^{2}

^{1} Observatoire de Haute-Provence,CNRS, F-04870
Saint-Michel l'Observatoire, France.
^{2} Laboratoire de Gravitation et Cosmologie Relativistes,
Université Pierre et Marie Curie
CNRS/ESA 7065, Tour 22/12, BP 142, 4 place Jussieu, F-75252 Paris Cedex 05,
France.

Astronomy & Astrophysics : Received 30 July 1998/Accepted 09 september 1998

Abstract:

We study the scintillation produced by time-varying gravitational fields within
scalar-tensor theories of gravity. The problem is treated in the geometrical
optics approximation for a very distant light source emitting quasi plane
monochromatic
electromagnetic waves. We obtain a general formula giving the time dependence
of the photon flux received by a freely falling observer. In the weak-field
approximation, we show that the contribution to the scintillation effect due to
the focusing of the light beam by a gravitational wave is of first order in the
amplitude of the scalar perturbation. Thus
scalar-tensor theories contrast with general relativity, which predicts that
the only first-order effect is due to the spectral shift. Moreover, we find
that the scintillation effects caused by the scalar field have a local
character: they depend only on the value of the perturbation at the observer.
This effect provides in principle a mean to detect the presence of a long range
scalar field in the Universe, but its smallness constitutes a tremendous
challenge for detection.

Key Words : Gravitation-Relativity-Methods:Observational-Techniques:photometric