Pseudoscalar couplings between Standard-Model quarks and dark matter are normally not considered relevant for dark-matter direct-detection experiments because they lead to velocity-suppressed scattering cross-sections in the non-relativistic limit. However, at the nucleon level, such couplings are effectively enhanced by factors of order O(mN /mq) ∼ 10 3 , where mN and mq are appropriate nucleon and quark masses respectively. This enhancement can thus be sufficient to overcome the corresponding velocity suppression, implying -contrary to common lore -that direct-detection experiments can indeed be sensitive to pseudoscalar couplings. In this work, we explain how this enhancement arises, and present a model-independent analysis of pseudoscalar interactions at directdetection experiments. We also identify those portions of the corresponding dark-matter parameter space which can be probed at current and future experiments of this type, and discuss the role of isospin violation in enhancing the corresponding experimental reach.

Dark matter can be gravitationally captured by the Sun after scattering off solar nuclei. Annihilations of the dark matter trapped and accumulated in the centre of the Sun could result in one of the most detectable and recognizable signals for dark matter. Searches for high-energy neutrinos produced in the decay of annihilation products have yielded extremely competitive constraints on the spin-dependent scattering cross sections of dark matter with nuclei. Recently, the low energy neutrino signal arising from dark-matter annihilation to quarks which then hadronize and shower has been suggested as a competitive and complementary search strategy. These high-multiplicity hadronic showers give rise to a large amount of pions which will come to rest in the Sun and decay, leading to a unique sub-GeV neutrino signal. We here improve on previous works by considering the monoenergetic neutrino signal arising from both pion and kaon decay. We consider searches at liquid scintillation, liquid argon, and water Cherenkov detectors and find very competitive sensitivities for few-GeV dark matter masses.

In single-component theories of dark matter, the 2 → 2 amplitudes for dark-matter production, annihilation, and scattering can be related to each other through various crossing symmetries. These crossing relations lie at the heart of the celebrated complementarity which underpins different existing dark-matter search techniques and strategies. In multi-component theories of dark matter, by contrast, there can be many different dark-matter components with differing masses. This then opens up a new, "diagonal" direction for dark-matter complementarity: the possibility of darkmatter decay from heavier to lighter dark-matter components. In this work, we discuss how this new direction may be correlated with the others, and demonstrate that the enhanced complementarity which emerges can be an important ingredient in probing and constraining the parameter spaces of such models.Introduction.-In recent years, many search techniques have been exploited in the hunt for dark matter [1]. These include possible dark-matter production at colliders; direct detection of cosmological dark matter through its scattering off ordinary matter at underground experiments; and indirect detection of dark matter through observation of the remnants of the annihilation of cosmological dark matter into ordinary matter at terrestrial or satellite-based experiments. At first glance, these different techniques may seem to rely on three independent properties of dark matter, namely its amplitudes for production, scattering, and annihilation. However, these three amplitudes are often related to each other through various crossing symmetries. As a result, the different corresponding search techniques are actually correlated with each other through their dependence on a single underlying interaction which couples dark matter to ordinary matter, and the results achieved through any one of these search techniques will have immediate implications for the others as well as for this underlying interaction. This is the origin of the celebrated complementarity which connects the different existing dark-matter search techniques (for a review, see Ref.[2]).

We consider the use of directionality in the search for monoenergetic sub-GeV neutrinos arising from the decay of stopped kaons, which can be produced by dark matter annihilation in the core of the Sun. When these neutrinos undergo charged-current interactions with a nucleus at a neutrino detector, they often eject a proton which is highly peaked in the forward direction. The direction of this track can be measured at DUNE, allowing one to distinguish signal from background by comparing on-source and off-source event rates. We find that directional information can enhance the signal to background ratio by up to a factor of 5.