38 research outputs found
Modelling the rotational curves of spiral galaxies with a scalar field
In a previous work (Mbelek 2001), we modelled the rotation curves (RC) of
spiral galaxies by including in the equation of motion of the stars the
dynamical terms from an external real self-interacting scalar field, ,
minimally coupled to gravity and which respects the equivalence principle in
the weak fields and low velocity approximation. This model appeared to have
three free parameters : the turnover radius, , the maximum tangential
velocity, , plus a strictly positive
integer, . Here, we propose a new improved version where the coupling of the
-field to dark matter is emphasized at the expense of its
self-interaction. This reformulation presents the very advantageous possibility
that the same potential is used for all galaxies. Using at the same time a
quasi-isothermal dark matter density and the scalar field helps to better fit
the RC of spiral galaxies. In addition, new correlations are established.Comment: Latex, 5 pages with 3 Postscript figure
Can conventional forces really explain the anomalous acceleration of Pioneer 10/11 ?
A conventional explanation of the correlation between the Pioneer 10/11
anomalous acceleration and spin-rate change is given. First, the rotational
Doppler shift analysis is improved. Finally, a relation between the radio beam
reaction force and the spin-rate change is established. Computations are found
in good agreement with observational data. The relevance of our result to the
main Pioneer 10/11 anomalous acceleration is emphasized. Our analysis leads us
to conclude that the latter may not be merely artificial.Comment: 9 pages, no figur
A viability criterion for modified gravity with an extra force
A recently proposed theory of modified gravity with an explicit ``anomalous''
coupling of the Ricci curvature to matter is discussed, and an inequality is
derived which expresses a necessary and sufficient condition to avoid the
notorius Dolgov-Kawasaki instability.Comment: 4 latex pages, to appear in Phys. Rev.