Misc,
An insight into the baryon-gravity relation in galaxies
(November 2006)
Abstract
Observations of spiral galaxies strongly support a one-to-one analytical
relation between the inferred gravity of dark matter at any radius and the
enclosed baryonic mass. It is baffling that baryons manage to settle the dark
matter gravitational potential in such a precise way, leaving no messy
fingerprints of the merging events and "gastrophysical" feedbacks expected in
the history of a galaxy in a concordance Universe. This correlation of gravity
with baryonic mass can be interpreted from several non-standard angles,
especially as a k-essence-like modification of gravity called TeVeS, in which
the baryon-gravity relation is captured by the dieletric-like function mu of
Modified Newtonian Dynamics (MOND). Here, after numerically addressing the
effects of non-spherical baryon geometry in the framework of non-linear TeVeS,
we investigate the observational constraints upon the mu-function from fitting
galaxy circular velocity curves, unveiling the degeneracy between the stellar
mass-to-light ratio and the mu-function, and discuss the implication of the
sharpness of transition from the strong to weak gravity regimes. On a purely
theoretical side, we exhaustively examine how the mu-function connects with the
free function of TeVeS. We also exhibit the important effects of renormalizing
the gravitational constant, and a discontinuity-free transition between
quasi-static galaxies and the evolving Universe. We then speculate on the
possible physical meaning of the mu-function in a TeVeS-like framework, and in
the framework of the recent proposal that dark matter could be made of
particles with a mass dipole moment.
