Relic Abundance of LKP Dark Matter in UED model including Effects of Second KK Resonances

Abstract

We reevaluate the thermal relic density of the Kaluza-Klein (KK) dark matter in universal extra dimension models. In particular, we consider the effect of the resonance caused by second KK particles on the density. We find that the annihilation cross sections relevant to the density are significantly enhanced due to the resonance when the Higgs boson mass is large enough (m_h \gtrsim 200 GeV). As a result, the mass of the dark matter particle consistent with the WMAP observation is increased compared to the result which does not include any resonance.

Figures (6)

• Figure 1: Contour plots of the mass splitting, $\delta \equiv (m_{h^{(2)}}-2m_{\gamma^{(1)}})/2m_{\gamma^{(1)}}$, in the ($1/R$, $m_h$) plane for $\Lambda R = 20$ (a) and for $\Lambda R = 50$ (b).
• Figure 2: Resonant annihilation process of LKP dark matter through $s$-channel $h^{(2)}$. The dominant one-loop diagrams to the $h^{(2)}-t-\bar{t}$ vertex stem from KK top quark--KK gluon mediation. Here $t$ is the zero mode of the top quark, and $t^{(n)}, T^{(n)}$ and $g^{(n)}$ are the $n$-th KK modes of left- and right-handed top quarks and gluon respectively.
• Figure 3: Thermally-averaged cross section as a function of the inverse of temperature $x = m/T$. Here we take $1/R = 700$ GeV and $\Lambda R = 20$ (a), and $1/R = 1000$ GeV and $\Lambda R = 50$ (b). In both Figs. (a) and (b), the dependence of the thermally-averaged cross section on the Higgs mass is shown. The dotted lines indicate the tree level results.
• Figure 4: Resonant one-loop diagram which appears in the coannihilation process.
• Figure 5: (a) Typical evolution of the abundance of LKP dark matter as a function of the temperature of the universe $x = m/T$. The dotted line indicates the abundance of the LKP at thermal equilibrium. (b) Ratio of the abundance $Y$ including the effect of the second KK resonance to that at the tree level $Y_{\rm tree}$ after the freeze-out $(20 < x < 400)$. Here we take $1/R = 1000$ GeV and $\Lambda R = 50$. Four lines correspond to the cases, $m_h = 120$ GeV (1), $200$ GeV (2), $250$ GeV (3) and $400$ GeV (4).