Elastic Scattering and Direct Detection of Kaluza-Klein Dark Matter

TL;DR

This paper investigates elastic scattering of Kaluza-Klein dark matter within Universal Extra Dimensions, focusing on the lightest KK particle (LKP) as a WIMP candidate. It shows that a KK neutrino LKP ($ u^{(1)}$) is excluded by relic-density requirements when confronted with direct-detection limits, while the $B^{(1)}$ LKP remains viable but yields small cross sections that depend on the LKP mass, KK-quark splitting, and the Higgs mass. The authors compute both scalar and spin contributions to the WIMP–nucleus cross section, including nuclear form factors, and provide predicted differential and integrated event rates for Ge, NaI, and Xe detectors, highlighting the need for multi-ton detectors to probe significant portions of the parameter space. They conclude that KK dark matter is testable in near-future experiments, with direct searches complementing collider and indirect-detection probes in exploring TeV-scale LKPs.

Abstract

Recently a new dark matter candidate has been proposed as a consequence of universal compact extra dimensions. It was found that to account for cosmological observations, the masses of the first Kaluza-Klein modes (and thus the approximate size of the extra dimension) should be in the range 600-1200 GeV when the lightest Kaluza-Klein particle (LKP) corresponds to the hypercharge boson and in the range 1 - 1.8 TeV when it corresponds to a neutrino. In this article, we compute the elastic scattering cross sections between Kaluza-Klein dark matter and nuclei both when the lightest Kaluza-Klein particle is a KK mode of a weak gauge boson, and when it is a neutrino. We include nuclear form factor effects which are important to take into account due to the large LKP masses favored by estimates of the relic density. We present both differential and integrated rates for present and proposed Germanium, NaI and Xenon detectors. Observable rates at current detectors are typically less than one event per year, but the next generation of detectors can probe a significant fraction of the relevant parameter space.

Figures (11)

• Figure 1: Leading Feynman graph for effective $\nu^{(1)}$-quark scattering through the exchange of a zero-mode Z gauge boson.
• Figure 2: Leading Feynman graph for effective $B^{(1)}$-quark scattering through the exchange of a zero-mode Higgs boson.
• Figure 3: Leading Feynman graphs for effective $B^{(1)}$-quark scattering through the exchange of a KK quark. Both $q^1_L$ and $q^1_R$ should be understood in each graph.
• Figure 4: Spin-dependent and spin-independent WIMP-nucleon cross sections as a function of the WIMP mass for (top to bottom) $\Delta=(m_{q^{(1)}}-m_{B^{(1)}})/m_{B^{(1)}}=5,10,15 \%$ and $m_h=120$ GeV.
• Figure 5: Scalar WIMP-nucleon cross section as a function of the Higgs mass for $m_{B^{(1)}}=1$ TeV and (top to bottom) $\Delta=(m_{q^{(1)}}-m_{B^{(1)}})/m_{B^{(1)}}=5,10,15 \%$.