Speaker
Description
General Relativity (GR) is the classical interpretation of gravitational interaction. Equivalently, GR can be represented as an effective field theory (EFT) of the non-trivial self-interacting theory of a massless spin-2 particle. The Planck mass sets the high-energy cutoff, which is where we expect to see the effects of quantum gravity. Various modifications to gravity significantly lower the cutoff energy by increasing the scaling of tree-level amplitudes. For instance, standard massive gravity has scaling ~ s^5 / (m^8 x (M_Pl)^2), whereas the de Rham-Gabadadze-Tolley (dRGT) model of massive gravity ameliorates this with a lower scaling ~ s^3 / (m^4 x (M_Pl)^2), where s is the Mandelstam centre-of-momentum energy squared. A compactified five-dimensional theory of gravity both preserves the scaling behaviour of general relativity and generates an infinite tower of massive spin-2 fields. These properties arise from the spontaneous breaking of diffeomorphism invariance, leaving residual symmetries that preserve the 5D scaling in the 4D EFT.
This presentation investigates the surprising properties found in the scattering amplitudes of massive spin-2 Kaluza-Klein modes and analyses their origins in the hidden symmetries inherent to the compactified five-dimensional gravity framework. We will also briefly discuss an extension in which an intermediate brane is placed in the 5D bulk, along with the resulting amplitude properties.
The behaviour of dark matter is further explored within a stabilised Randall-Sundrum model, in which dark matter is localised on the TeV brane and interacts with both spin-2 Kaluza-Klein and spin-0 Goldberger-Wise modes. Constraints from relic density, collider searches, and direct-detection experiments strongly constrain spin-2 Kaluza-Klein portal models. Nevertheless, some regions of parameter space remain viable, primarily due to the effects of the massive radion arising from geometric stabilisation. These regions correspond to either a light (~1-5 GeV) or a heavy (~0.1-1 TeV) radion.