Generalized Dilaton Couplings to Dark Matter

Inspired by recent models of inflation within the Jordan-Brans-Dicke theory, namely the ``generalized extended inflation'' models (see Holman, Kolb, Vadas and Wang [Phys. Lett. B 250 (1990) 24; Phys. Rev. D 43 (1991) 995]), we propose generalized couplings of a dark matter component to the Jordan-Brans-Dicke, or dilaton, field. Assuming the dark matter component to be dominant today we use observational data on the rate of change of Newton's constant, as well as on its value during primordial nucleosynthesis, on the age of the Universe and on the present value of the Hubble constant to put limits on these couplings. Our results extended previous ones by Damour, Gibbons and Gundlach [Phys. Rev. Lett. 64 (1990) 123]. Unlike all previously considered models, the Newton constant would change with time even if the universe were dominated by an invisible radiation-like component (i.e., whose energy-momentum tensor has vanishing trace). Using a lagrangian approach we propose a natural coupling of the dilaton field to a perfect fluid dark matter component.