| In this dissertation, I use the success of the standard model of big-bang nucleosynthesis to examine the effects of interacting particle species and the effect of varying coupling constants, predicted by theories set in extra dimensions, on primordial nucleosynthesis. A review is given of the standard model and of the abundances of the light elements expected to be produced in the early Universe. The weakest piece of the concordance between the standard model of big-bang nucleosynthesis and observation is the production and primordial abundance of {dollar}sp7{dollar}Li. Therefore I discuss the production of {dollar}sp7{dollar}Li in astrophysical environments other than the early Universe and show that the predictions of big-bang nucleosynthesis, when supplemented by those due to astrophysical sources, are in good agreement with observation.; I then show that the effect on big-bang nucleosynthesis of an additional particle species which remains coupled to either photons or light neutrinos can be quite different from that predicted by the equivalent number of neutrino species parameterization, which does work for decoupled additional species. In particular I consider the case of an additional axion-like particle and show that its effect is to decrease the amount of {dollar}sp4{dollar}He produced in the big-bang.; In addition, I consider the effects of varying coupling constants on {dollar}sp4{dollar}He production in the big-bang and show that constraining Y{dollar}sb p{dollar} = 0.24 {dollar}pm{dollar} 0.01 leads to a constraint on the time variation of the fine-structure constant of {dollar}vert d{dollar}ln {dollar}alpha/dtvert <{dollar} 2 {dollar}times{dollar} 10{dollar}sp{lcub}-14{rcub}{dollar}. Using a similar technique, I show that by using theories which make definite predictions about the relationship between the values of coupling constants and the scale of compactified space (e.g., Kaluza-Klein and superstring theories), one can constrain the scale of extra dimensions by satisfying Y{dollar}sb p{dollar} = 0.24 {dollar}pm{dollar} 0.01. I find that the scale of extra dimensions must have been within 1.0% of their size today at the time of primordial nucleosynthesis. |
