Status of inelastic dark matter

In light of recent positive results from the DAMA experiment, as well as new null results from CDMS Soudan, Edelweiss, ZEPLIN-I and CRESST, we reexamine the framework of inelastic dark matter with a standard halo. In this framework, which was originally introduced to reconcile tensions between CDMS and DAMA, dark matter particles can scatter off of nuclei only by making a transition to a nearly degenerate state that is roughly $100\mathrm{keV}$ heavier. We find that recent data significantly constrains the parameter space of the framework, but that there are still regions consistent with all experimental results. Because of the enhanced annual modulation and dramatically different energy dependence in this scenario, we emphasize the need for greater information on the dates of data taking, and on the energy distribution of signal and background. We also study the specific case of “mixed-sneutrino” dark matter, and isolate regions of parameter space which are cosmologically interesting for that particular model. A significant improvement in limits by heavy target experiments such as ZEPLIN or CRESST should be able to confirm or exclude the inelastic dark matter scenario in the near future. Within the mixed-sneutrino model, an elastic scattering signature should be seen at upcoming germanium experiments, including future results from CDMS Soudan.

Figure 1

The suppression of signal in the energy range $10\mathrm{keV}<E_R<150\mathrm{keV}$ for $m_{\chi }=70\mathrm{GeV}$ and $\delta =100\mathrm{keV}$ as a function of the atomic number of the target.

Figure 2

The suppression of signal as a function of energy at a germanium experiment, with $m_{\chi }=120\mathrm{GeV}$ and $\delta =80\mathrm{keV}$.

Figure 3

(a) The spectrum of signal at a germanium experiment as a function of energy, with area normalized to one. Shown are $m_{\chi }=100\mathrm{GeV}$ with $\delta =80\mathrm{keV}$ compared with the elastic scattering case. b) Spectrum of the modulated signal at DAMA for $m_{\chi }=90\mathrm{GeV}$ and $\delta =140\mathrm{keV}$ compared with the elastic case. In both cases, the thin, solid line is the inelastic case, and the dashed, thick line is the elastic case. The sharp cutoff in (b) arises due to the finite galactic escape, and would be smoothed with a more realistic cutoff. The histogram shows the integrated signal in the corresponding bins, which is less sensitive to the details of the cutoff.

Figure 4

Amplitude of modulation as a percentage of the unmodulated signal at DAMA as a function of $\delta$, with $m_{\chi }=90\mathrm{GeV}$.

Figure 5

Allowed regions in ${\sigma }_n$, $\delta$ parameter space for $m_{\chi }=$ (a) 75 GeV (b) 100 GeV  (c) 120 GeV (d) 250 GeV (e) 500 GeV. The light and dark shaded regions have ${\chi }^2<9,4$ as described in the text. The thick solid line is the CDMS limit. The dashed, curved line gives the CRESST results, and the thin solid line gives the preliminary ZEPLIN-I limit. The horizontal dashed line applies to the mixed-sneutrino model, and is the upper bound on ${\sigma }_n$ derived by considering the relic abundance, as described in the text.