UBC Theses and Dissertations
On the Yukawa interaction as a slow, gravity-like force Loggia, Elizabeth
The nature of dark matter continues to be one of the most elusive mysteries in physics. The astrophysical and cosmological support for dark matter seems overwhelming, but all of the current observational evidence is from only the gravitational influence on baryonic matter. According to the standard cosmology, dark matter is five times as prevalent as baryonic matter, where, taking the contribution from dark energy in to account, only 5% of our universe is made of baryonic matter. Ongoing experimental searches for particle dark matter have provided only constraints without direct detection. As such, alternative theories to dark matter need to be explored. One such alternative idea is an emergent gravity theory. Gravity, no longer a fundamental interaction, emerges from thermodynamic principles in the form of an entropic force. When this theory is applied to cosmology, the gravitational effect that we observe and attribute to dark matter is rather a memory effect from the emergence of space; it is an intrinsic property of the spacetime itself. As it is unclear how to proceed from this theory in general, a proper framework is required so that we can eventually make testable predictions. We propose that the addition of a slow, gravity-like force to general relativity is such a framework. We establish that the Yukawa interaction is gravity-like in certain limits, from both a particle physics and a general relativity perspective, where the massless Yukawa field has infinite range. Exploring spherical collapse in Einstein-de Sitter cosmology, we show that the addition of the Yukawa interaction does not affect the overall evolution of the density contrast, except to decrease the time to collapse. We consider the equations of motion for a massive scalar field coupled to a massless scalar Yukawa field, and plot the solutions as functions of the scale factor. The resulting plots have distinct behaviour before and after the scale factor is of the same magnitude as the coupling. Finally, we consider the effects of a slow, gravity-like force and derive the Lagrangian density for a slow, massless scalar field.
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