New Constraints on Dark Matter Effective Theories from Standard Model Loops

We consider an effective field theory for a gauge singlet Dirac dark matter particle interacting with the standard model fields via effective operators suppressed by the scale $\mathrm{\Lambda }\gtrsim 1\mathrm{TeV}$. We perform a systematic analysis of the leading loop contributions to spin-independent Dirac dark matter–nucleon scattering using renormalization group evolution between $\mathrm{\Lambda }$ and the low-energy scale probed by direct detection experiments. We find that electroweak interactions induce operator mixings such that operators that are naively velocity suppressed and spin dependent can actually contribute to spin-independent scattering. This allows us to put novel constraints on Wilson coefficients that were so far poorly bounded by direct detection. Constraints from current searches are already significantly stronger than LHC bounds, and will improve in the near future. Interestingly, the loop contribution we find is isospin violating even if the underlying theory is isospin conserving.

Figure 1

Diagrams responsible for the mixing of $O_{qq}^{VA}$ into $O_{HHD}^V$. Graphs originated by crossing or reversing the fermion flow are not displayed.

Figure 2

From bottom to top, thick lines: Lower bounds for allowed regions from LHC searches [57] (dashed, orange), SI WIMP–nucleon scattering from XENON100 (solid, green) [62] and LUX (solid, red) [63] and projected allowed regions for SCDMS [65] (dot-dashed, purple) and XENON1T [66] (dot-dashed, blue). The curve giving the correct thermal relic density (thin black line) is also shown is also shown. Here we set $C_{qq}^{VA}=1$ while all other Wilson coefficients are assumed to be zero.

Figure 3

Regions in parameter space allowed by LUX [63] for $\mathrm{\Lambda }=10\mathrm{TeV}$ (blue), $20\mathrm{TeV}$ (red), and $30\mathrm{TeV}$ (yellow), assuming flavor universality in the DM-quark coupling. In the case of nonuniversal couplings, $C_{qq}^{VA}$ should be replaced by $C_{tt}^{VA}$. The dark matter mass is fixed to $100\mathrm{GeV}$.