Scattering Amplitudes in Theories of Compactified Gravity

Abstract: In this dissertation we discuss the properties of matrix elements describing the scattering of massive spin-2 particles in theories of compactified gravity. Our primary result is the calculation of 2-to-2 massive spin-2 Kaluza-Klein (KK) mode scattering matrix elements in the Randall-Sundrum 1 (RS1) model and the demonstration that those matrix elements grow no faster than $\mathcal{O}(s)$ irrespective of the KK mode numbers and helicities considered. Because this calculation requires summing infinitely-many spin-2 mediated diagrams which each diverge like $\mathcal{O}(s^{5})$, overall $\mathcal{O}(s)$ growth is only attained through cancellations between these diagrams. This in turn requires intricate cancellations between infinitely-many KK mode masses and couplings. We derive these sum rules, including their generalization to fully inelastic processes. We also consider these matrix elements in the five-dimensional orbifolded torus (5DOT) and large $kr_{c}$ limits, investigate the impact of including only finitely-many diagrams in the calculation (as measured via truncation error), and calculate the five-dimensional strong coupling scale $\Lambda_{\pi} \equiv M_{\text{Pl}}\, e^{-kr_{c}\pi}$ via the four-dimensional scattering calculation.