Nucleosynthesis constraints on a scale-dependent new intermediate range interaction

We derive constraints on the strength of a new intermediate range interaction that couples to baryon number from primordial nucleosynthesis yields. The nucleosysnthesis limits here used arise from matching observations and predictions of standard and inhomogeneous primordial scenarios. We show that the standard nucleosynthesis scenario is more restrictive (alpha(5) less than or similar to 0.2) when the range of the interaction is greater than about 1 m. We further discuss the implications of considering the scalar particle responsible for the new interaction as the main component of the dark matter in the galactic halo such that its decay can account for the ionization of hydrogen in the interstellar medium and the temperature of Lyman-alpha clouds. (C) 1999 Elsevier Science B.V. All rights reserved.