Isospin-violating dark matter in the light of recent data

In scenarios where dark matter interacts differently with protons and neutrons (isospin-violating dark matter), the interpretation of the experimental limits on the dark matter spin-independent cross section may be significantly modified. On the one hand, the direct detection constraints are shifted depending on the target nucleus, possibly changing the hierarchy among different experiments. On the other hand, the relative strength between the bounds from neutrino detectors and those from direct detection experiments is altered, allowing the former to be more competitive. In this paper, the status of isospin-violating dark matter is assessed in the light of recent data, and the prospects for its detection in the near future are analyzed. We find, for example, that there are regions in the parameter space where IceCube currently provides the most stringent limits on the spin-independent cross section, or others where the expected sensitivity of DEAP-3600 is well above the LUX exclusion limit. Our results highlight the complementarity among different targets in direct detection experiments, and between direct detection and neutrino searches in the quest for a dark matter signal.

Figure 1

The solid lines show the recent constraints on the dark matter–proton spin-independent cross section for $f_n/f_p=1$ (isospin conservation) from different direct detection experiments: CDMS II (orange), DS50 (yellow), XENON100 (magenta), PandaX (cyan), and LUX (red). The dotted lines show instead the expected sensitivity in currently running direct detection experiments: DS50 (light blue), DEAP-3600 (green), and XENON1T (blue).

Figure 2

A summary of the constraints on the dark matter–proton spin-independent cross section obtained recently in neutrino detectors. The colors of the lines distinguish the experiments—Super-Kamiokande (green), ANTARES (red), and IceCube (light and dark blue)—whereas the type of line indicates the final state from dark matter annihilations: ${\tau }^{+}{\tau }^{-}$ (solid) and $W^{+}{W}^{-}$ (dashed). To facilitate the comparison with Fig. 1, we have kept the same scale.

Figure 3

The function $F_Z(f_n/f_p)$ for xenon, argon, and germanium targets and $f_n/f_p\in (-1,1)$. $F_Z(f_n/f_p)$ is the factor by which the sensitivity of a direct detection experiment to the dark matter–proton spin-independent cross section is reduced for isospin-violating dark matter.

Figure 4

Current limits and expected sensitivities to the dark matter–proton spin-independent cross section for $f_n/f_p=-0.7$. This value of $f_n/f_p$ maximally suppresses the sensitivity of xenon targets. The conventions are the same as in Fig. 1. Notice that, for this value of $f_n/f_p$, the current bound from DarkSide50 is comparable to the one from LUX at high masses. In addition, DEAP-3600 is expected to probe a much larger region of parameter space than XENON1T.

Figure 5

A comparison between direct detection and IceCube bounds on the dark matter–proton spin-independent cross section for $f_n/f_p=-0.7$. Notice that, in this case, IceCube bounds can be significantly stronger than the direct detection ones. In fact, IceCube has already excluded some regions of the parameter space that lie beyond the expected reach of XENON1T.

Figure 6

A comparison between direct detection and IceCube bounds on the dark matter–proton spin-independent cross section for $f_n/f_p=-0.65$.

Figure 7

A comparison between direct detection and IceCube bounds on the dark matter–proton spin-independent cross section for $f_n/f_p=-0.75$.

Figure 8

A comparison between direct detection and IceCube bounds on the dark matter–proton spin-independent cross section for $f_n/f_p=-0.6$.

Figure 9

A comparison between direct detection and IceCube bounds on the dark matter–proton spin-independent cross section for $f_n/f_p=-0.8$.