Abstract
WIMP-nucleon scattering is analyzed at order 1/M in Heavy WIMP Effective Theory. The 1/M power corrections, where M≫mW is the WIMP mass, distinguish between different underlying UV models with the same universal limit and their impact on direct detection rates can be enhanced relative to naive expectations due to generic amplitude-level cancellations at leading order. The necessary one- and two-loop matching calculations onto the low-energy effective theory for WIMP interactions with Standard Model quarks and gluons are performed for the case of an electroweak SU(2) triplet WIMP, considering both the cases of elementary fermions and composite scalars. The low-velocity WIMP-nucleon scattering cross section is evaluated and compared with current experimental limits and projected future sensitivities. Our results provide the most robust prediction for electroweak triplet Majorana fermion dark matter direct detection rates; for this case, a cancellation between two sources of power corrections yields a small total 1/M correction, and a total cross section close to the universal limit for M≳few×100GeV. For the SU(2) composite scalar, the 1/M corrections introduce dependence on underlying strong dynamics. Using a leading chiral logarithm evaluation, the total 1/M correction has a larger magnitude and uncertainty than in the fermionic case, with a sign that further suppresses the total cross section. These examples provide definite targets for future direct detection experiments and motivate large scale detectors capable of probing to the neutrino floor in the TeV mass regime.
Highlights
The WIMP paradigm remains a leading explanation for astrophysical dark matter [1,2,3,4,5,6,7]
We introduce the shorthand notation ci = (π α22/m3W )ci for the effective operator coefficients, xi = mi/mW for masses expressed in units of mW, subscripts U and D denote arbitrary up-type (u, c or t) or down-type (d, s or b) quarks, respectively, and N = 2 is the number of massless Standard Model generations
LHC bounds have pushed the scale of new physics into a regime of large mass where direct detection is more challenging; at the same time, universal predictions emerge in this regime and provide well-defined targets for generation searches
Summary
The WIMP paradigm remains a leading explanation for astrophysical dark matter [1,2,3,4,5,6,7]. Null results at the LHC [8,9,10,11] suggest that new physics is heavy compared to masses of weak scale particles, ∼ 100 GeV Two of the authors (RJH and MPS) analyzed the universal heavy WIMP limit for WIMP-nucleon scattering [29,30,31,32] In this limit a generic amplitude-level cancellation [29,30,33] was shown to suppress the low-velocity WIMPnucleon cross section to the level of ∼10−47 cm for wino-like WIMPs (i.e., self-conjugate electroweak triplets), and higgsino-like cross sections to an even smaller value. Before investigating the impact of these differences on direct detection cross sections, let us perform the remaining step of matching HWET onto effective QCD operators
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