Nucleosynthesis constraints on a scale-dependent new intermediate range interaction

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