UBC Theses and Dissertations

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UBC Theses and Dissertations

Dimensionless cosmology Narimani, Ali


The variability of fundamental physical constants has been a topic of interest both theoretically and experimentally for many years. Although it is interesting to investigate the consequences of such a variation, it is important to realise that only the variation of dimensionless combination of constants can be meaningfully measured and discussed. In this thesis, I try to justify this way of thinking and apply it to two basic cosmological observables, Big Bang Nucleosynthesis and Cosmic Microwave Background anisotropies. I will mention some related studies that are either wrong or not complete because of being dimensionful. Variation of constants could be considered on two different levels. On the first level one assumes that the constants are time invariant but they can assume different values in different Universes or patches of sky. A thought experiment describing a discussion with aliens having a different system of units with different coupling constants could be helpful, this idea will be returned to throughout the thesis. On the next level, the constants can be promoted to being smooth functions of time or space. It is good to have a firm understanding of what happens on the previous level before trying to consider genuinely variable constants. For variable constants we need to consider theories beyond the currently accepted ones, which are capable of consistently describing such a variation. I briefly review the scalar-tensor theory of gravity as a possible way to describe the variation of the gravitational coupling. I give a brief historical review on the subject and consider the theory in the two so called ‘frames’, discussing about the benefits of each frame mathematically and the physical meaning of these frames. Such theories could form the frame work in which further study of variable con- stants could be carried out.

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