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Register a new userAnalysis strategies for general spin-independent WIMP-nucleus scattering
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We propose a formalism for the analysis of direct-detection dark-matter searches that covers all coherent responses for scalar and vector interactions and incorporates QCD constraints imposed by chiral symmetry, including all one- and two-body WIMP-nucleon interactions up to third order in chiral effective field theory. One of the free parameters in the WIMP-nucleus cross section corresponds to standard spin-independent searches, but in general different combinations of new-physics couplings are probed. We identify the interference with the isovector counterpart of the standard spin-independent response and two-body currents as the dominant corrections to the leading spin-independent structure factor, and discuss the general consequences for the interpretation of direct-detection experiments, including minimal extensions of the standard spin-independent analysis. Fits for all structure factors required for the scattering off xenon targets are provided based on state-of-the-art nuclear shell-model calculations.
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We present nuclear structure factors that describe the generalized spin-independent coupling of weakly interacting massive particles (WIMPs) to nuclei. Our results are based on state-of-the-art nuclear structure calculations using the large-scale nuclear shell model. Starting from quark- and gluon-level operators, we consider all possible coherently enhanced couplings of spin-1/2 and spin-0 WIMPs to one and two nucleons up to third order in chiral effective field theory. This includes a comprehensive discussion of the structure factors corresponding to the leading two-nucleon currents covering, for the first time, the contribution of spin-2 operators. We provide results for the most relevant nuclear targets considered in present and planned dark matter direct detection experiments: fluorine, silicon, argon, and germanium, complementing our previous work on xenon. All results are also publicly available in a Python notebook.
We study the structure factors for spin-independent WIMP scattering off xenon based on state-of-the-art large-scale shell-model calculations, which are shown to yield a good spectroscopic description of all experimentally relevant isotopes. Our results are based on the leading scalar one-body currents only. At this level and for the momentum transfers relevant to direct dark matter detection, the structure factors are in very good agreement with the phenomenological Helm form factors used to give experimental limits for WIMP-nucleon cross sections. In contrast to spin-dependent WIMP scattering, the spin-independent channel, at the one-body level, is less sensitive to nuclear structure details. In addition, we explicitly show that the structure factors for inelastic scattering are suppressed by ~ 10^{-4} compared to the coherent elastic scattering response. This implies that the detection of inelastic scattering will be able to discriminate clearly between spin-independent and spin-dependent scattering. Finally, we provide fits for all calculated structure factors.
The communitys reliance on simplified descriptions of WIMP-nucleus interactions reflects the absence of analysis tools that integrate general theories of dark matter with standard treatments of nuclear response functions. To bridge this gap, we have constructed a public-domain Mathematica package for WIMP analyses based on our effective theory formulation. Script inputs are 1) the coefficients of the effective theory, through which one can characterize the low-energy consequences of arbitrary ultraviolet theories of WIMP interactions; and 2) one-body density matrices for commonly used targets, the most compact description of the relevant nuclear physics. The generality of the effective theory expansion guarantees that the script will remain relevant as new ultraviolet theories are explored; the use of density matrices to factor the nuclear physics from the particle physics will allow nuclear structure theorists to update the script as new calculations become available, independent of specific particle-physics contexts. The Mathematica package outputs the resulting response functions (and associated form factors) and also the differential event rate, once a galactic WIMP velocity profile is specified, and thus in its present form provides a complete framework for experimental analysis. The Mathematica script requires no a priori knowledge of the details of the non-relativistic effective field theory or nuclear physics, though the core concepts are reviewed here and in arXiv:1203.3542.
In this paper, as the first part of the third step of our study on developing data analysis procedures for using 3-dimensional information offered by directional direct Dark Matter detection experiments in the future, we present our double-Monte Carlo scattering-by-scattering simulation of the 3-dimensional elastic WIMP-nucleus scattering process, which can provide 3-D velocity information (the magnitude, the direction, and the incoming/scattering time) of each incident halo WIMP as well as the recoil direction and the recoil energy of the scattered target nucleus in different celestial coordinate systems. For readers reference, (animated) simulation plots with different WIMP masses and several frequently used target nuclei for all functionable underground laboratories can be found and downloaded on our online (interactive) demonstration webpage (http://www.tir.tw/phys/hep/dm/amidas-2d/).
We propose a new mechanism where asymmetric dark matter (ADM) and the baryon asymmetry are both generated in the same decay chain of a metastable weakly interacting massive particle (WIMP) after its thermal freeze-out. Dark matter and baryons are connected by a generalized baryon number that is conserved, while the DM asymmetry and baryon asymmetry compensate each other. This unified framework addresses the DM-baryon coincidence while inheriting the merit of the conventional WIMP miracle in predicting relic abundances of matter. Examples of renormalizable models realizing this scenario are presented. These models generically predict ADM with sub-GeV to GeV-scale mass that interacts with Standard Model quarks or leptons, thus rendering potential signatures at direct detection experiments sensitive to low mass DM. Other interesting phenomenological predictions are also discussed, including: LHC signatures of new intermediate particles with color or electroweak charge and DM induced nucleon decay; the long-lived WIMP may be within reach of future high energy collider experiments.
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