UC Riverside

Effective field theory is arguably one of the most powerful theoretical tools that we have at our disposal as physicists. It enables us to describe the low-energy physics of a wide range of models with relatively few operators. In this thesis, we show how so-called "irrelevant" (higher-dimension) EFT operators lead to a number of novel, yet under-appreciated properties, both in flat and negatively-curved Anti de-Sitter spacetime. In flat space, higher-dimension EFT operators give rise to spin-dependent quantum forces which arise at loop level. We determine these forces and show how they can be used to probe specific models of dark matter. We point out that the oft-discussed spin-dependent Yukawa forces have specific properties and are not representative of the behavior of generic potentials. Quantum forces from irrelevant EFT operators can and should serve as complimentary benchmark cases when discussing potential bounds from various fifth-force experiments. We discuss how the neutrino force, a famous example of a quantum force, can be used to determine the Dirac/Majorana origin of the neutrino mass.

In (4+1)-dimensional Anti de-Sitter spacetime, we show how the presence of higher-dimension EFT operators implies a number of novel properties for bulk particles. These include soft, high multiplicity cascade decays known as soft bombs and the merging of spectral resonances into a continuum at high energies. The negative curvature of AdS warps momentum scales, leading to a puzzle where particles created in one part of the space can appear to be outside the region of EFT invalidity in another part of the space. We provide the resolution to this puzzle and demonstrate the self-consistency of the EFT.