Limits on Kaluza-Klein Portal Dark Matter Models

TL;DR

This paper analyzes Kaluza-Klein portal dark matter models within Randall-Sundrum frameworks, showing scalar models are ruled out while fermion and vector models remain viable under specific conditions, with detailed calculations and new couplings discussed.

Contribution

It provides a comprehensive analysis of KK graviton-mediated dark matter models, including new calculations of KK-graviton couplings and constraints on scalar, fermion, and vector dark matter.

Findings

Scalar dark matter models are ruled out in the thermal freeze-out scenario.

Vector dark matter is viable for masses 1.1-5.5 TeV with KK coupling scales up to 40 TeV.

Fermion dark matter is viable for similar masses with KK scales around 20 TeV.

Abstract

We revisit the phenomenology of dark-matter (DM) scenarios within radius-stabilized Randall-Sundrum models. Specifically, we consider models where the dark matter candidates are Standard Model (SM) singlets confined to the TeV brane and interact with the SM via spin-2 and spin-0 gravitational Kaluza-Klein (KK) modes. We compute the thermal relic density of DM particles in these models by applying recent work showing that scattering amplitudes of massive spin-2 KK states involve an intricate cancellation between various diagrams. Considering the resulting DM abundance, collider searches, and the absence of a signal in direct DM detection experiments, we show that spin-2 KK portal DM models are highly constrained. We confirm that within the usual thermal freeze-out scenario, scalar dark matter models are essentially ruled out. In contrast, we show that fermion and vector dark matter models are viable in a region of parameter space in which dark matter annihilation through a KK graviton is resonant. Specifically, vector models are viable for dark matter masses ranging from 1.1 TeV to 5.5 TeV for theories in which the scale of couplings of the KK modes is of order 40 TeV or lower. Fermion dark matter models are viable for a similar mass region, but only for KK coupling scales of order 20 TeV. In this work, we provide a complete description of the calculations needed to arrive at these results and, in an appendix, a discussion of new KK-graviton couplings needed for the computations, which have not previously been discussed in the literature. Here, we focus on models in which the radion is light, and the back-reaction of the radion stabilization dynamics on the gravitational background can be neglected. The phenomenology of a model with a heavy radion and the consideration of the effects of the radion stabilization dynamics on the DM abundance are being addressed in forthcoming work.